{"kind": "plan", "major": "18", "item": {"slug": "group", "name": "Group", "name_zh": "Group", "category": "Aggregation", "summary": "Groups an ordered input stream by its grouping columns.", "aliases": ["Group", "T_Group"], "content_hash": "416e3ab8f1dcba42ca83b9d6d8d13107ea763e26250afcd2b26631c28618622f", "versions": {"10": {"facts": [{"label": "Core node tag", "value": "T_Group"}, {"label": "Structured EXPLAIN Node Type", "value": "Group"}, {"label": "Inputs", "value": "One ordered child plan"}, {"label": "Output", "value": "One tuple per group"}, {"label": "Executor initializer", "value": "ExecInitGroup"}, {"label": "Memory mechanism", "value": "unclassified"}], "memory": {"evidence": [{"url": "https://ftp.postgresql.org/pub/source/v10.23/postgresql-10.23.tar.bz2", "path": "src/backend/executor/nodeGroup.c", "label": "src/backend/executor/nodeGroup.c", "sha256": "48e010c544e3601ba93ac6234bc3a75edd2a928ed9c289ad9eca1bb480546def", "archive_sha256": "94a4b2528372458e5662c18d406629266667c437198160a18cdfd2c4a4d6eee9"}], "mechanism": "unclassified", "description": "This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider.", "source_notes": []}, "tables": [{"key": "explain-labels", "rows": [{"label": "Group", "identity": "Group"}], "title": "EXPLAIN labels in this source build", "columns": [{"key": "label", "label": "Text-format label"}, {"key": "identity", "label": "Structured node identity"}]}], "related": [{"url": "/wiki/sql/explain/?v=10", "label": "EXPLAIN"}, {"url": "/docs/10/using-explain.html", "label": "Using EXPLAIN"}, {"url": "/docs/10/parallel-plans.html", "label": "Parallel plans"}], "release": {"ref": "PostgreSQL 10.23 source archive", "label": "10.23", "major": "10", "channel": "historical", "revision": "94a4b2528372458e5662c18d406629266667c437198160a18cdfd2c4a4d6eee9", "source_url": "https://ftp.postgresql.org/pub/source/v10.23/postgresql-10.23.tar.bz2", "source_snapshot_utc": ""}, "sources": [{"url": "https://ftp.postgresql.org/pub/source/v10.23/postgresql-10.23.tar.bz2", "line": 1019, "path": "src/backend/commands/explain.c", "label": "src/backend/commands/explain.c:1019", "sha256": "a785298532047cfeda969e78c3597a343dc1c56d61ba85830b0f16a02a14b5a1", "archive_sha256": "94a4b2528372458e5662c18d406629266667c437198160a18cdfd2c4a4d6eee9"}, {"url": "https://ftp.postgresql.org/pub/source/v10.23/postgresql-10.23.tar.bz2", "line": 318, "path": "src/backend/executor/execProcnode.c", "label": "src/backend/executor/execProcnode.c:318", "sha256": "cea76648bb38ae55f18f989768bee1a4ee025691ceea0f86bccb29dcdc166acc", "archive_sha256": "94a4b2528372458e5662c18d406629266667c437198160a18cdfd2c4a4d6eee9"}, {"url": "https://ftp.postgresql.org/pub/source/v10.23/postgresql-10.23.tar.bz2", "path": "src/backend/executor/nodeGroup.c", "label": "src/backend/executor/nodeGroup.c", "sha256": "48e010c544e3601ba93ac6234bc3a75edd2a928ed9c289ad9eca1bb480546def", "archive_sha256": "94a4b2528372458e5662c18d406629266667c437198160a18cdfd2c4a4d6eee9"}, {"url": "https://ftp.postgresql.org/pub/source/v10.23/postgresql-10.23.tar.bz2", "path": "src/include/nodes/plannodes.h", "label": "src/include/nodes/plannodes.h", "sha256": "d562c321108844798cd234303fffb618f13d4ee3f3a5ac79bfd963b077e47c22", "archive_sha256": "94a4b2528372458e5662c18d406629266667c437198160a18cdfd2c4a4d6eee9"}, {"url": "/docs/10/parallel-plans.html#PARALLEL-AGGREGATION", "path": "parallel-plans.html", "label": "PostgreSQL 10.23 \u00b7 parallel-plans", "sha256": "cd37ed0ef7e2cf177707f50d9a7258574b4cefdcc087e6ee99a3bf377d960fcb"}], "node_tag": "T_Group", "sections": [{"title": "EXPLAIN names and attributes", "paragraphs": ["Structured formats use the Node Type above. Text-format spellings can also include operation, strategy, join type, scan direction or aggregation-stage attributes.", "Text names recorded by this source: Group.", "Parallel-aware and parallel-safe are different plan properties. A node running inside a parallel worker is not necessarily a parallel-aware node."]}, {"title": "Memory and temporary storage", "paragraphs": ["This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider."]}, {"title": "Parallel execution and instrumentation", "paragraphs": ["The source callbacks below can coordinate execution or collect worker instrumentation. Their presence is not a blanket claim that this node supports a shared parallel scan or shared state.", "Callbacks in this build: none extracted from this node implementation."]}, {"title": "Same-version manual discussion", "paragraphs": ["PostgreSQL supports parallel aggregation by aggregating in two stages. First, each process participating in the parallel portion of the query performs an aggregation step, producing a partial result for each group of which that process is aware. This is reflected in the plan as a Partial Aggregate node. Second, the partial results are transferred to the leader via Gather or Gather Merge . Finally, the leader re-aggregates the results across all workers in order to produce the final result. This is reflected in the plan as a Finalize Aggregate node."]}, {"title": "Executor implementation notes", "paragraphs": ["nodeGroup.c Routines to handle group nodes (used for queries with GROUP BY clause).", "DESCRIPTION The Group node is designed for handling queries with a GROUP BY clause. Its outer plan must deliver tuples that are sorted in the order specified by the grouping columns (ie. tuples from the same group are consecutive). That way, we just have to compare adjacent tuples to locate group boundaries.", "The ScanTupleSlot holds the (copied) first tuple of each group.", "We need not call ResetExprContext here because execTuplesMatch will reset the per-tuple memory context once per input tuple.", "If first time through, acquire first input tuple and determine whether to return it or not."]}, {"code": "case T_Group:\n\t\t\tpname = sname = \"Group\";\n\t\t\tbreak;", "title": "EXPLAIN identity in core source"}], "strategies": [], "description": ["Groups an ordered input stream by its grouping columns."], "evidence_kind": "source and documentation", "explain_names": ["Group"], "partial_modes": [], "comparison_data": {"node_tag": "T_Group", "strategies": [], "text_names": ["Group"], "initializer": "ExecInitGroup", "partial_modes": [], "memory_mechanism": "unclassified", "parallel_callbacks": []}, "comparison_hash": "c75b880801aecfa8f510650c6bb3c2e0aa820810550fefe9c62d04727c0c0048", "explain_prefixes": ["Parallel"], "runtime_verified": false, "source_inventory": {"explain": "src/backend/commands/explain.c", "executor": "src/backend/executor/execProcnode.c", "implementation": "src/backend/executor/nodeGroup.c"}, "parallel_callbacks": []}, "11": {"facts": [{"label": "Core node tag", "value": "T_Group"}, {"label": "Structured EXPLAIN Node Type", "value": "Group"}, {"label": "Inputs", "value": "One ordered child plan"}, {"label": "Output", "value": "One tuple per group"}, {"label": "Executor initializer", "value": "ExecInitGroup"}, {"label": "Memory mechanism", "value": "unclassified"}], "memory": {"evidence": [{"url": "https://ftp.postgresql.org/pub/source/v11.22/postgresql-11.22.tar.bz2", "path": "src/backend/executor/nodeGroup.c", "label": "src/backend/executor/nodeGroup.c", "sha256": "22df06a5733ddc185d129eb05f3e0268a239ea5272889b215dc1a768d09b0f7d", "archive_sha256": "2cb7c97d7a0d7278851bbc9c61f467b69c094c72b81740b751108e7892ebe1f0"}], "mechanism": "unclassified", "description": "This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider.", "source_notes": []}, "tables": [{"key": "explain-labels", "rows": [{"label": "Group", "identity": "Group"}], "title": "EXPLAIN labels in this source build", "columns": [{"key": "label", "label": "Text-format label"}, {"key": "identity", "label": "Structured node identity"}]}], "related": [{"url": "/wiki/sql/explain/?v=11", "label": "EXPLAIN"}, {"url": "/docs/11/using-explain.html", "label": "Using EXPLAIN"}, {"url": "/docs/11/parallel-plans.html", "label": "Parallel plans"}], "release": {"ref": "PostgreSQL 11.22 source archive", "label": "11.22", "major": "11", "channel": "historical", "revision": "2cb7c97d7a0d7278851bbc9c61f467b69c094c72b81740b751108e7892ebe1f0", "source_url": "https://ftp.postgresql.org/pub/source/v11.22/postgresql-11.22.tar.bz2", "source_snapshot_utc": ""}, "sources": [{"url": "https://ftp.postgresql.org/pub/source/v11.22/postgresql-11.22.tar.bz2", "line": 1144, "path": "src/backend/commands/explain.c", "label": "src/backend/commands/explain.c:1144", "sha256": "9df8400c1a4377179572ceb916d6020fca4e2760f74bf416d77ed97476523bbd", "archive_sha256": "2cb7c97d7a0d7278851bbc9c61f467b69c094c72b81740b751108e7892ebe1f0"}, {"url": "https://ftp.postgresql.org/pub/source/v11.22/postgresql-11.22.tar.bz2", "line": 318, "path": "src/backend/executor/execProcnode.c", "label": "src/backend/executor/execProcnode.c:318", "sha256": "95ef4d4a5df4c29f14af9763fae2c530449bdacdf3853d9ff297adf1fed6153b", "archive_sha256": "2cb7c97d7a0d7278851bbc9c61f467b69c094c72b81740b751108e7892ebe1f0"}, {"url": "https://ftp.postgresql.org/pub/source/v11.22/postgresql-11.22.tar.bz2", "path": "src/backend/executor/nodeGroup.c", "label": "src/backend/executor/nodeGroup.c", "sha256": "22df06a5733ddc185d129eb05f3e0268a239ea5272889b215dc1a768d09b0f7d", "archive_sha256": "2cb7c97d7a0d7278851bbc9c61f467b69c094c72b81740b751108e7892ebe1f0"}, {"url": "https://ftp.postgresql.org/pub/source/v11.22/postgresql-11.22.tar.bz2", "path": "src/include/nodes/plannodes.h", "label": "src/include/nodes/plannodes.h", "sha256": "5e0511194183800e8d6eb293fd4b40639c7d3118e2d199c8e7865ba4fa4cf67f", "archive_sha256": "2cb7c97d7a0d7278851bbc9c61f467b69c094c72b81740b751108e7892ebe1f0"}, {"url": "/docs/11/parallel-plans.html#PARALLEL-AGGREGATION", "path": "parallel-plans.html", "label": "PostgreSQL 11.22 \u00b7 parallel-plans", "sha256": "353df5869034b7665159a74037d9cf3e1800d15efcea3390daaa99aae89fa288"}], "node_tag": "T_Group", "sections": [{"title": "EXPLAIN names and attributes", "paragraphs": ["Structured formats use the Node Type above. Text-format spellings can also include operation, strategy, join type, scan direction or aggregation-stage attributes.", "Text names recorded by this source: Group.", "Parallel-aware and parallel-safe are different plan properties. A node running inside a parallel worker is not necessarily a parallel-aware node."]}, {"title": "Memory and temporary storage", "paragraphs": ["This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider."]}, {"title": "Parallel execution and instrumentation", "paragraphs": ["The source callbacks below can coordinate execution or collect worker instrumentation. Their presence is not a blanket claim that this node supports a shared parallel scan or shared state.", "Callbacks in this build: none extracted from this node implementation."]}, {"title": "Same-version manual discussion", "paragraphs": ["PostgreSQL supports parallel aggregation by aggregating in two stages. First, each process participating in the parallel portion of the query performs an aggregation step, producing a partial result for each group of which that process is aware. This is reflected in the plan as a Partial Aggregate node. Second, the partial results are transferred to the leader via Gather or Gather Merge . Finally, the leader re-aggregates the results across all workers in order to produce the final result. This is reflected in the plan as a Finalize Aggregate node."]}, {"title": "Executor implementation notes", "paragraphs": ["nodeGroup.c Routines to handle group nodes (used for queries with GROUP BY clause).", "DESCRIPTION The Group node is designed for handling queries with a GROUP BY clause. Its outer plan must deliver tuples that are sorted in the order specified by the grouping columns (ie. tuples from the same group are consecutive). That way, we just have to compare adjacent tuples to locate group boundaries.", "The ScanTupleSlot holds the (copied) first tuple of each group.", "We need not call ResetExprContext here because ExecQualAndReset() will reset the per-tuple memory context once per input tuple.", "If first time through, acquire first input tuple and determine whether to return it or not."]}, {"code": "case T_Group:\n\t\t\tpname = sname = \"Group\";\n\t\t\tbreak;", "title": "EXPLAIN identity in core source"}], "strategies": [], "description": ["Groups an ordered input stream by its grouping columns."], "evidence_kind": "source and documentation", "explain_names": ["Group"], "partial_modes": [], "comparison_data": {"node_tag": "T_Group", "strategies": [], "text_names": ["Group"], "initializer": "ExecInitGroup", "partial_modes": [], "memory_mechanism": "unclassified", "parallel_callbacks": []}, "comparison_hash": "c75b880801aecfa8f510650c6bb3c2e0aa820810550fefe9c62d04727c0c0048", "explain_prefixes": ["Parallel"], "runtime_verified": false, "source_inventory": {"explain": "src/backend/commands/explain.c", "executor": "src/backend/executor/execProcnode.c", "implementation": "src/backend/executor/nodeGroup.c"}, "parallel_callbacks": []}, "12": {"facts": [{"label": "Core node tag", "value": "T_Group"}, {"label": "Structured EXPLAIN Node Type", "value": "Group"}, {"label": "Inputs", "value": "One ordered child plan"}, {"label": "Output", "value": "One tuple per group"}, {"label": "Executor initializer", "value": "ExecInitGroup"}, {"label": "Memory mechanism", "value": "unclassified"}], "memory": {"evidence": [{"url": "https://ftp.postgresql.org/pub/source/v12.22/postgresql-12.22.tar.bz2", "path": "src/backend/executor/nodeGroup.c", "label": "src/backend/executor/nodeGroup.c", "sha256": "4086fc1c320a832fe2baaf1324d0ef6a0de267deeb56e47b7a8f6a78e3dad567", "archive_sha256": "8df3c0474782589d3c6f374b5133b1bd14d168086edbc13c6e72e67dd4527a3b"}], "mechanism": "unclassified", "description": "This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider.", "source_notes": []}, "tables": [{"key": "explain-labels", "rows": [{"label": "Group", "identity": "Group"}], "title": "EXPLAIN labels in this source build", "columns": [{"key": "label", "label": "Text-format label"}, {"key": "identity", "label": "Structured node identity"}]}], "related": [{"url": "/wiki/sql/explain/?v=12", "label": "EXPLAIN"}, {"url": "/docs/12/using-explain.html", "label": "Using EXPLAIN"}, {"url": "/docs/12/parallel-plans.html", "label": "Parallel plans"}], "release": {"ref": "PostgreSQL 12.22 source archive", "label": "12.22", "major": "12", "channel": "historical", "revision": "8df3c0474782589d3c6f374b5133b1bd14d168086edbc13c6e72e67dd4527a3b", "source_url": "https://ftp.postgresql.org/pub/source/v12.22/postgresql-12.22.tar.bz2", "source_snapshot_utc": ""}, "sources": [{"url": "https://ftp.postgresql.org/pub/source/v12.22/postgresql-12.22.tar.bz2", "line": 1215, "path": "src/backend/commands/explain.c", "label": "src/backend/commands/explain.c:1215", "sha256": "d02ea84fdaa201de5d9360645a9f24bfbd2c31f7d45a639e09560ac0e6b6471d", "archive_sha256": "8df3c0474782589d3c6f374b5133b1bd14d168086edbc13c6e72e67dd4527a3b"}, {"url": "https://ftp.postgresql.org/pub/source/v12.22/postgresql-12.22.tar.bz2", "line": 318, "path": "src/backend/executor/execProcnode.c", "label": "src/backend/executor/execProcnode.c:318", "sha256": "311b17379fe54e3f342fe5ad41c43afbdfa1b844978db2bb2eb22b82520d3256", "archive_sha256": "8df3c0474782589d3c6f374b5133b1bd14d168086edbc13c6e72e67dd4527a3b"}, {"url": "https://ftp.postgresql.org/pub/source/v12.22/postgresql-12.22.tar.bz2", "path": "src/backend/executor/nodeGroup.c", "label": "src/backend/executor/nodeGroup.c", "sha256": "4086fc1c320a832fe2baaf1324d0ef6a0de267deeb56e47b7a8f6a78e3dad567", "archive_sha256": "8df3c0474782589d3c6f374b5133b1bd14d168086edbc13c6e72e67dd4527a3b"}, {"url": "https://ftp.postgresql.org/pub/source/v12.22/postgresql-12.22.tar.bz2", "path": "src/include/nodes/plannodes.h", "label": "src/include/nodes/plannodes.h", "sha256": "b0c4a0aeb48660ce06e5e700d5529ca9066fd16682bd15783d6e71b5420b07b0", "archive_sha256": "8df3c0474782589d3c6f374b5133b1bd14d168086edbc13c6e72e67dd4527a3b"}, {"url": "/docs/12/parallel-plans.html#PARALLEL-AGGREGATION", "path": "parallel-plans.html", "label": "PostgreSQL 12.22 \u00b7 parallel-plans", "sha256": "fa33380814ee65998f524524f8681d70cf3b1198d54b39847b00462b01517ffb"}], "node_tag": "T_Group", "sections": [{"title": "EXPLAIN names and attributes", "paragraphs": ["Structured formats use the Node Type above. Text-format spellings can also include operation, strategy, join type, scan direction or aggregation-stage attributes.", "Text names recorded by this source: Group.", "Parallel-aware and parallel-safe are different plan properties. A node running inside a parallel worker is not necessarily a parallel-aware node."]}, {"title": "Memory and temporary storage", "paragraphs": ["This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider."]}, {"title": "Parallel execution and instrumentation", "paragraphs": ["The source callbacks below can coordinate execution or collect worker instrumentation. Their presence is not a blanket claim that this node supports a shared parallel scan or shared state.", "Callbacks in this build: none extracted from this node implementation."]}, {"title": "Same-version manual discussion", "paragraphs": ["PostgreSQL supports parallel aggregation by aggregating in two stages. First, each process participating in the parallel portion of the query performs an aggregation step, producing a partial result for each group of which that process is aware. This is reflected in the plan as a Partial Aggregate node. Second, the partial results are transferred to the leader via Gather or Gather Merge . Finally, the leader re-aggregates the results across all workers in order to produce the final result. This is reflected in the plan as a Finalize Aggregate node."]}, {"title": "Executor implementation notes", "paragraphs": ["nodeGroup.c Routines to handle group nodes (used for queries with GROUP BY clause).", "DESCRIPTION The Group node is designed for handling queries with a GROUP BY clause. Its outer plan must deliver tuples that are sorted in the order specified by the grouping columns (ie. tuples from the same group are consecutive). That way, we just have to compare adjacent tuples to locate group boundaries.", "The ScanTupleSlot holds the (copied) first tuple of each group.", "We need not call ResetExprContext here because ExecQualAndReset() will reset the per-tuple memory context once per input tuple.", "If first time through, acquire first input tuple and determine whether to return it or not."]}, {"code": "case T_Group:\n\t\t\tpname = sname = \"Group\";\n\t\t\tbreak;", "title": "EXPLAIN identity in core source"}], "strategies": [], "description": ["Groups an ordered input stream by its grouping columns."], "evidence_kind": "source and documentation", "explain_names": ["Group"], "partial_modes": [], "comparison_data": {"node_tag": "T_Group", "strategies": [], "text_names": ["Group"], "initializer": "ExecInitGroup", "partial_modes": [], "memory_mechanism": "unclassified", "parallel_callbacks": []}, "comparison_hash": "c75b880801aecfa8f510650c6bb3c2e0aa820810550fefe9c62d04727c0c0048", "explain_prefixes": ["Parallel"], "runtime_verified": false, "source_inventory": {"explain": "src/backend/commands/explain.c", "executor": "src/backend/executor/execProcnode.c", "implementation": "src/backend/executor/nodeGroup.c"}, "parallel_callbacks": []}, "13": {"facts": [{"label": "Core node tag", "value": "T_Group"}, {"label": "Structured EXPLAIN Node Type", "value": "Group"}, {"label": "Inputs", "value": "One ordered child plan"}, {"label": "Output", "value": "One tuple per group"}, {"label": "Executor initializer", "value": "ExecInitGroup"}, {"label": "Memory mechanism", "value": "unclassified"}], "memory": {"evidence": [{"url": "https://ftp.postgresql.org/pub/source/v13.23/postgresql-13.23.tar.bz2", "path": "src/backend/executor/nodeGroup.c", "label": "src/backend/executor/nodeGroup.c", "sha256": "38ffe517ca9a2177a06bf023ea6836776a955baed1096c6f2d28e0ccb0494fbc", "archive_sha256": "6ec3c82726af92b7dec873fa1cdf881eca92a4219787dfad05acb6b10e041fd6"}], "mechanism": "unclassified", "description": "This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider.", "source_notes": []}, "tables": [{"key": "explain-labels", "rows": [{"label": "Group", "identity": "Group"}], "title": "EXPLAIN labels in this source build", "columns": [{"key": "label", "label": "Text-format label"}, {"key": "identity", "label": "Structured node identity"}]}], "related": [{"url": "/wiki/sql/explain/?v=13", "label": "EXPLAIN"}, {"url": "/docs/13/using-explain.html", "label": "Using EXPLAIN"}, {"url": "/docs/13/parallel-plans.html", "label": "Parallel plans"}], "release": {"ref": "PostgreSQL 13.23 source archive", "label": "13.23", "major": "13", "channel": "historical", "revision": "6ec3c82726af92b7dec873fa1cdf881eca92a4219787dfad05acb6b10e041fd6", "source_url": "https://ftp.postgresql.org/pub/source/v13.23/postgresql-13.23.tar.bz2", "source_snapshot_utc": ""}, "sources": [{"url": "https://ftp.postgresql.org/pub/source/v13.23/postgresql-13.23.tar.bz2", "line": 1276, "path": "src/backend/commands/explain.c", "label": "src/backend/commands/explain.c:1276", "sha256": "541713e0e7f1c9cc352c2b6028964d440c19d2678a4463000094c24a88c1e730", "archive_sha256": "6ec3c82726af92b7dec873fa1cdf881eca92a4219787dfad05acb6b10e041fd6"}, {"url": "https://ftp.postgresql.org/pub/source/v13.23/postgresql-13.23.tar.bz2", "line": 323, "path": "src/backend/executor/execProcnode.c", "label": "src/backend/executor/execProcnode.c:323", "sha256": "d085ee99acfa00587e6ade3a1d9f8108a0566beedbbee3f54a50c9fc0cc2e875", "archive_sha256": "6ec3c82726af92b7dec873fa1cdf881eca92a4219787dfad05acb6b10e041fd6"}, {"url": "https://ftp.postgresql.org/pub/source/v13.23/postgresql-13.23.tar.bz2", "path": "src/backend/executor/nodeGroup.c", "label": "src/backend/executor/nodeGroup.c", "sha256": "38ffe517ca9a2177a06bf023ea6836776a955baed1096c6f2d28e0ccb0494fbc", "archive_sha256": "6ec3c82726af92b7dec873fa1cdf881eca92a4219787dfad05acb6b10e041fd6"}, {"url": "https://ftp.postgresql.org/pub/source/v13.23/postgresql-13.23.tar.bz2", "path": "src/include/nodes/plannodes.h", "label": "src/include/nodes/plannodes.h", "sha256": "dcb296833777b02008c4b6bae8e8f7c6423b7ffba21f36702597c9d596d039ab", "archive_sha256": "6ec3c82726af92b7dec873fa1cdf881eca92a4219787dfad05acb6b10e041fd6"}, {"url": "/docs/13/parallel-plans.html#PARALLEL-AGGREGATION", "path": "parallel-plans.html", "label": "PostgreSQL 13.23 \u00b7 parallel-plans", "sha256": "025ad8564a8461b676c9153f9e084429cca0ef86c968090689b082120060f3d0"}], "node_tag": "T_Group", "sections": [{"title": "EXPLAIN names and attributes", "paragraphs": ["Structured formats use the Node Type above. Text-format spellings can also include operation, strategy, join type, scan direction or aggregation-stage attributes.", "Text names recorded by this source: Group.", "Parallel-aware and parallel-safe are different plan properties. A node running inside a parallel worker is not necessarily a parallel-aware node."]}, {"title": "Memory and temporary storage", "paragraphs": ["This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider."]}, {"title": "Parallel execution and instrumentation", "paragraphs": ["The source callbacks below can coordinate execution or collect worker instrumentation. Their presence is not a blanket claim that this node supports a shared parallel scan or shared state.", "Callbacks in this build: none extracted from this node implementation."]}, {"title": "Same-version manual discussion", "paragraphs": ["PostgreSQL supports parallel aggregation by aggregating in two stages. First, each process participating in the parallel portion of the query performs an aggregation step, producing a partial result for each group of which that process is aware. This is reflected in the plan as a Partial Aggregate node. Second, the partial results are transferred to the leader via Gather or Gather Merge . Finally, the leader re-aggregates the results across all workers in order to produce the final result. This is reflected in the plan as a Finalize Aggregate node."]}, {"title": "Executor implementation notes", "paragraphs": ["nodeGroup.c Routines to handle group nodes (used for queries with GROUP BY clause).", "DESCRIPTION The Group node is designed for handling queries with a GROUP BY clause. Its outer plan must deliver tuples that are sorted in the order specified by the grouping columns (ie. tuples from the same group are consecutive). That way, we just have to compare adjacent tuples to locate group boundaries.", "The ScanTupleSlot holds the (copied) first tuple of each group.", "We need not call ResetExprContext here because ExecQualAndReset() will reset the per-tuple memory context once per input tuple.", "If first time through, acquire first input tuple and determine whether to return it or not."]}, {"code": "case T_Group:\n\t\t\tpname = sname = \"Group\";\n\t\t\tbreak;", "title": "EXPLAIN identity in core source"}], "strategies": [], "description": ["Groups an ordered input stream by its grouping columns."], "evidence_kind": "source and documentation", "explain_names": ["Group"], "partial_modes": [], "comparison_data": {"node_tag": "T_Group", "strategies": [], "text_names": ["Group"], "initializer": "ExecInitGroup", "partial_modes": [], "memory_mechanism": "unclassified", "parallel_callbacks": []}, "comparison_hash": "c75b880801aecfa8f510650c6bb3c2e0aa820810550fefe9c62d04727c0c0048", "explain_prefixes": ["Parallel"], "runtime_verified": false, "source_inventory": {"explain": "src/backend/commands/explain.c", "executor": "src/backend/executor/execProcnode.c", "implementation": "src/backend/executor/nodeGroup.c"}, "parallel_callbacks": []}, "14": {"facts": [{"label": "Core node tag", "value": "T_Group"}, {"label": "Structured EXPLAIN Node Type", "value": "Group"}, {"label": "Inputs", "value": "One ordered child plan"}, {"label": "Output", "value": "One tuple per group"}, {"label": "Executor initializer", "value": "ExecInitGroup"}, {"label": "Memory mechanism", "value": "unclassified"}], "memory": {"evidence": [{"url": "https://ftp.postgresql.org/pub/source/v14.24/postgresql-14.24.tar.bz2", "path": "src/backend/executor/nodeGroup.c", "label": "src/backend/executor/nodeGroup.c", "sha256": "86100527e3ac8007217e438fc749300601a255bc90fcd4f03bdcca7ff4a7e447", "archive_sha256": "a7fa7ed3d558172355f51406097a7bd4f6b473be80f311ef7cda96bf383d8897"}], "mechanism": "unclassified", "description": "This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider.", "source_notes": []}, "tables": [{"key": "explain-labels", "rows": [{"label": "Group", "identity": "Group"}], "title": "EXPLAIN labels in this source build", "columns": [{"key": "label", "label": "Text-format label"}, {"key": "identity", "label": "Structured node identity"}]}], "related": [{"url": "/wiki/sql/explain/?v=14", "label": "EXPLAIN"}, {"url": "/docs/14/using-explain.html", "label": "Using EXPLAIN"}, {"url": "/docs/14/parallel-plans.html", "label": "Parallel plans"}], "release": {"ref": "PostgreSQL 14.24 source archive", "label": "14.24", "major": "14", "channel": "stable", "revision": "a7fa7ed3d558172355f51406097a7bd4f6b473be80f311ef7cda96bf383d8897", "source_url": "https://ftp.postgresql.org/pub/source/v14.24/postgresql-14.24.tar.bz2", "source_snapshot_utc": ""}, "sources": [{"url": "https://ftp.postgresql.org/pub/source/v14.24/postgresql-14.24.tar.bz2", "line": 1318, "path": "src/backend/commands/explain.c", "label": "src/backend/commands/explain.c:1318", "sha256": "e091be4e2a083b8dea39ccd09beedede22c1716ef974da66c214a44f48be8c41", "archive_sha256": "a7fa7ed3d558172355f51406097a7bd4f6b473be80f311ef7cda96bf383d8897"}, {"url": "https://ftp.postgresql.org/pub/source/v14.24/postgresql-14.24.tar.bz2", "line": 335, "path": "src/backend/executor/execProcnode.c", "label": "src/backend/executor/execProcnode.c:335", "sha256": "72da1c5ad457f1d92a39ab73531701794df858419e3b89d6e6cb7079634e68fa", "archive_sha256": "a7fa7ed3d558172355f51406097a7bd4f6b473be80f311ef7cda96bf383d8897"}, {"url": "https://ftp.postgresql.org/pub/source/v14.24/postgresql-14.24.tar.bz2", "path": "src/backend/executor/nodeGroup.c", "label": "src/backend/executor/nodeGroup.c", "sha256": "86100527e3ac8007217e438fc749300601a255bc90fcd4f03bdcca7ff4a7e447", "archive_sha256": "a7fa7ed3d558172355f51406097a7bd4f6b473be80f311ef7cda96bf383d8897"}, {"url": "https://ftp.postgresql.org/pub/source/v14.24/postgresql-14.24.tar.bz2", "path": "src/include/nodes/plannodes.h", "label": "src/include/nodes/plannodes.h", "sha256": "302f51a16b570dba7ec4e7bc045f7df5800d21630280354d1a24025f3baec75d", "archive_sha256": "a7fa7ed3d558172355f51406097a7bd4f6b473be80f311ef7cda96bf383d8897"}, {"url": "/docs/14/parallel-plans.html#PARALLEL-AGGREGATION", "path": "parallel-plans.html", "label": "PostgreSQL 14.24 \u00b7 parallel-plans", "sha256": "71fc3525781b74150364925e123cd8598fdebe0e05326706f2bc2e1ffa0b88a4"}], "node_tag": "T_Group", "sections": [{"title": "EXPLAIN names and attributes", "paragraphs": ["Structured formats use the Node Type above. Text-format spellings can also include operation, strategy, join type, scan direction or aggregation-stage attributes.", "Text names recorded by this source: Group.", "Parallel-aware and parallel-safe are different plan properties. A node running inside a parallel worker is not necessarily a parallel-aware node."]}, {"title": "Memory and temporary storage", "paragraphs": ["This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider."]}, {"title": "Parallel execution and instrumentation", "paragraphs": ["The source callbacks below can coordinate execution or collect worker instrumentation. Their presence is not a blanket claim that this node supports a shared parallel scan or shared state.", "Callbacks in this build: none extracted from this node implementation."]}, {"title": "Same-version manual discussion", "paragraphs": ["PostgreSQL supports parallel aggregation by aggregating in two stages. First, each process participating in the parallel portion of the query performs an aggregation step, producing a partial result for each group of which that process is aware. This is reflected in the plan as a Partial Aggregate node. Second, the partial results are transferred to the leader via Gather or Gather Merge . Finally, the leader re-aggregates the results across all workers in order to produce the final result. This is reflected in the plan as a Finalize Aggregate node."]}, {"title": "Executor implementation notes", "paragraphs": ["nodeGroup.c Routines to handle group nodes (used for queries with GROUP BY clause).", "DESCRIPTION The Group node is designed for handling queries with a GROUP BY clause. Its outer plan must deliver tuples that are sorted in the order specified by the grouping columns (ie. tuples from the same group are consecutive). That way, we just have to compare adjacent tuples to locate group boundaries.", "The ScanTupleSlot holds the (copied) first tuple of each group.", "We need not call ResetExprContext here because ExecQualAndReset() will reset the per-tuple memory context once per input tuple.", "If first time through, acquire first input tuple and determine whether to return it or not."]}, {"code": "case T_Group:\n\t\t\tpname = sname = \"Group\";\n\t\t\tbreak;", "title": "EXPLAIN identity in core source"}], "strategies": [], "description": ["Groups an ordered input stream by its grouping columns."], "evidence_kind": "source and documentation", "explain_names": ["Group"], "partial_modes": [], "comparison_data": {"node_tag": "T_Group", "strategies": [], "text_names": ["Group"], "initializer": "ExecInitGroup", "partial_modes": [], "memory_mechanism": "unclassified", "parallel_callbacks": []}, "comparison_hash": "c75b880801aecfa8f510650c6bb3c2e0aa820810550fefe9c62d04727c0c0048", "explain_prefixes": ["Parallel", "Async"], "runtime_verified": false, "source_inventory": {"explain": "src/backend/commands/explain.c", "executor": "src/backend/executor/execProcnode.c", "implementation": "src/backend/executor/nodeGroup.c"}, "parallel_callbacks": []}, "15": {"facts": [{"label": "Core node tag", "value": "T_Group"}, {"label": "Structured EXPLAIN Node Type", "value": "Group"}, {"label": "Inputs", "value": "One ordered child plan"}, {"label": "Output", "value": "One tuple per group"}, {"label": "Executor initializer", "value": "ExecInitGroup"}, {"label": "Memory mechanism", "value": "unclassified"}], "memory": {"evidence": [{"url": "https://ftp.postgresql.org/pub/source/v15.19/postgresql-15.19.tar.bz2", "path": "src/backend/executor/nodeGroup.c", "label": "src/backend/executor/nodeGroup.c", "sha256": "fe2b6f000c8b63acad78c9e5b673a7918d057e414f4c734d5d4be7f4fd87e96c", "archive_sha256": "e1a64a87a46b825b88c082e4518161a47aab53c45694964f8ba1df28f7859f89"}], "mechanism": "unclassified", "description": "This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider.", "source_notes": []}, "tables": [{"key": "explain-labels", "rows": [{"label": "Group", "identity": "Group"}], "title": "EXPLAIN labels in this source build", "columns": [{"key": "label", "label": "Text-format label"}, {"key": "identity", "label": "Structured node identity"}]}], "related": [{"url": "/wiki/sql/explain/?v=15", "label": "EXPLAIN"}, {"url": "/docs/15/using-explain.html", "label": "Using EXPLAIN"}, {"url": "/docs/15/parallel-plans.html", "label": "Parallel plans"}], "release": {"ref": "PostgreSQL 15.19 source archive", "label": "15.19", "major": "15", "channel": "stable", "revision": "e1a64a87a46b825b88c082e4518161a47aab53c45694964f8ba1df28f7859f89", "source_url": "https://ftp.postgresql.org/pub/source/v15.19/postgresql-15.19.tar.bz2", "source_snapshot_utc": ""}, "sources": [{"url": "https://ftp.postgresql.org/pub/source/v15.19/postgresql-15.19.tar.bz2", "line": 1321, "path": "src/backend/commands/explain.c", "label": "src/backend/commands/explain.c:1321", "sha256": "bb3b442d0f1b098aa8707335250102f027a596cd94117308bd16d1d36b258f5c", "archive_sha256": "e1a64a87a46b825b88c082e4518161a47aab53c45694964f8ba1df28f7859f89"}, {"url": "https://ftp.postgresql.org/pub/source/v15.19/postgresql-15.19.tar.bz2", "line": 335, "path": "src/backend/executor/execProcnode.c", "label": "src/backend/executor/execProcnode.c:335", "sha256": "19836c50a272741a4eac653541e655437c2e00710a541e5348d6a277d0669d7c", "archive_sha256": "e1a64a87a46b825b88c082e4518161a47aab53c45694964f8ba1df28f7859f89"}, {"url": "https://ftp.postgresql.org/pub/source/v15.19/postgresql-15.19.tar.bz2", "path": "src/backend/executor/nodeGroup.c", "label": "src/backend/executor/nodeGroup.c", "sha256": "fe2b6f000c8b63acad78c9e5b673a7918d057e414f4c734d5d4be7f4fd87e96c", "archive_sha256": "e1a64a87a46b825b88c082e4518161a47aab53c45694964f8ba1df28f7859f89"}, {"url": "https://ftp.postgresql.org/pub/source/v15.19/postgresql-15.19.tar.bz2", "path": "src/include/nodes/plannodes.h", "label": "src/include/nodes/plannodes.h", "sha256": "fb4a4c8165495299131173680bc02a950d88e1ff610231fd97997bc0c9afc1d7", "archive_sha256": "e1a64a87a46b825b88c082e4518161a47aab53c45694964f8ba1df28f7859f89"}, {"url": "/docs/15/parallel-plans.html#PARALLEL-AGGREGATION", "path": "parallel-plans.html", "label": "PostgreSQL 15.19 \u00b7 parallel-plans", "sha256": "ec9345488a15cdc05d3e0b0849763e2bf0b864ad17de786c5f023db5dab1ea96"}], "node_tag": "T_Group", "sections": [{"title": "EXPLAIN names and attributes", "paragraphs": ["Structured formats use the Node Type above. Text-format spellings can also include operation, strategy, join type, scan direction or aggregation-stage attributes.", "Text names recorded by this source: Group.", "Parallel-aware and parallel-safe are different plan properties. A node running inside a parallel worker is not necessarily a parallel-aware node."]}, {"title": "Memory and temporary storage", "paragraphs": ["This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider."]}, {"title": "Parallel execution and instrumentation", "paragraphs": ["The source callbacks below can coordinate execution or collect worker instrumentation. Their presence is not a blanket claim that this node supports a shared parallel scan or shared state.", "Callbacks in this build: none extracted from this node implementation."]}, {"title": "Same-version manual discussion", "paragraphs": ["PostgreSQL supports parallel aggregation by aggregating in two stages. First, each process participating in the parallel portion of the query performs an aggregation step, producing a partial result for each group of which that process is aware. This is reflected in the plan as a Partial Aggregate node. Second, the partial results are transferred to the leader via Gather or Gather Merge . Finally, the leader re-aggregates the results across all workers in order to produce the final result. This is reflected in the plan as a Finalize Aggregate node."]}, {"title": "Executor implementation notes", "paragraphs": ["nodeGroup.c Routines to handle group nodes (used for queries with GROUP BY clause).", "DESCRIPTION The Group node is designed for handling queries with a GROUP BY clause. Its outer plan must deliver tuples that are sorted in the order specified by the grouping columns (ie. tuples from the same group are consecutive). That way, we just have to compare adjacent tuples to locate group boundaries.", "The ScanTupleSlot holds the (copied) first tuple of each group.", "We need not call ResetExprContext here because ExecQualAndReset() will reset the per-tuple memory context once per input tuple.", "If first time through, acquire first input tuple and determine whether to return it or not."]}, {"code": "case T_Group:\n\t\t\tpname = sname = \"Group\";\n\t\t\tbreak;", "title": "EXPLAIN identity in core source"}], "strategies": [], "description": ["Groups an ordered input stream by its grouping columns."], "evidence_kind": "source and documentation", "explain_names": ["Group"], "partial_modes": [], "comparison_data": {"node_tag": "T_Group", "strategies": [], "text_names": ["Group"], "initializer": "ExecInitGroup", "partial_modes": [], "memory_mechanism": "unclassified", "parallel_callbacks": []}, "comparison_hash": "c75b880801aecfa8f510650c6bb3c2e0aa820810550fefe9c62d04727c0c0048", "explain_prefixes": ["Parallel", "Async"], "runtime_verified": false, "source_inventory": {"explain": "src/backend/commands/explain.c", "executor": "src/backend/executor/execProcnode.c", "implementation": "src/backend/executor/nodeGroup.c"}, "parallel_callbacks": []}, "16": {"facts": [{"label": "Core node tag", "value": "T_Group"}, {"label": "Structured EXPLAIN Node Type", "value": "Group"}, {"label": "Inputs", "value": "One ordered child plan"}, {"label": "Output", "value": "One tuple per group"}, {"label": "Executor initializer", "value": "ExecInitGroup"}, {"label": "Memory mechanism", "value": "unclassified"}], "memory": {"evidence": [{"url": "https://ftp.postgresql.org/pub/source/v16.15/postgresql-16.15.tar.bz2", "path": "src/backend/executor/nodeGroup.c", "label": "src/backend/executor/nodeGroup.c", "sha256": "1b9fab8f2dfcdf55eb5789646fed7a4c18d5678719bd52c4d84a9dd1dd60650c", "archive_sha256": "c1575341fa7bd40f5274ea465b34390f4dc64cdd0770af327005caaeb9f6b7ed"}], "mechanism": "unclassified", "description": "This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider.", "source_notes": []}, "tables": [{"key": "explain-labels", "rows": [{"label": "Group", "identity": "Group"}], "title": "EXPLAIN labels in this source build", "columns": [{"key": "label", "label": "Text-format label"}, {"key": "identity", "label": "Structured node identity"}]}], "related": [{"url": "/wiki/sql/explain/?v=16", "label": "EXPLAIN"}, {"url": "/docs/16/using-explain.html", "label": "Using EXPLAIN"}, {"url": "/docs/16/parallel-plans.html", "label": "Parallel plans"}], "release": {"ref": "PostgreSQL 16.15 source archive", "label": "16.15", "major": "16", "channel": "stable", "revision": "c1575341fa7bd40f5274ea465b34390f4dc64cdd0770af327005caaeb9f6b7ed", "source_url": "https://ftp.postgresql.org/pub/source/v16.15/postgresql-16.15.tar.bz2", "source_snapshot_utc": ""}, "sources": [{"url": "https://ftp.postgresql.org/pub/source/v16.15/postgresql-16.15.tar.bz2", "line": 1354, "path": "src/backend/commands/explain.c", "label": "src/backend/commands/explain.c:1354", "sha256": "8e017f0116dbea471339b40c37a667cc9f95039e7e0329c783e5e8ce194de7e1", "archive_sha256": "c1575341fa7bd40f5274ea465b34390f4dc64cdd0770af327005caaeb9f6b7ed"}, {"url": "https://ftp.postgresql.org/pub/source/v16.15/postgresql-16.15.tar.bz2", "line": 335, "path": "src/backend/executor/execProcnode.c", "label": "src/backend/executor/execProcnode.c:335", "sha256": "e48c08e555f8cb4e4bb43df516c4b8906ce9bc374b2a745d98a1fc8c22cc5099", "archive_sha256": "c1575341fa7bd40f5274ea465b34390f4dc64cdd0770af327005caaeb9f6b7ed"}, {"url": "https://ftp.postgresql.org/pub/source/v16.15/postgresql-16.15.tar.bz2", "path": "src/backend/executor/nodeGroup.c", "label": "src/backend/executor/nodeGroup.c", "sha256": "1b9fab8f2dfcdf55eb5789646fed7a4c18d5678719bd52c4d84a9dd1dd60650c", "archive_sha256": "c1575341fa7bd40f5274ea465b34390f4dc64cdd0770af327005caaeb9f6b7ed"}, {"url": "https://ftp.postgresql.org/pub/source/v16.15/postgresql-16.15.tar.bz2", "path": "src/include/nodes/plannodes.h", "label": "src/include/nodes/plannodes.h", "sha256": "97db47353db76326b874589a5ad0a04501cc74cd72e237e7bd956e7472c41f1f", "archive_sha256": "c1575341fa7bd40f5274ea465b34390f4dc64cdd0770af327005caaeb9f6b7ed"}, {"url": "/docs/16/parallel-plans.html#PARALLEL-AGGREGATION", "path": "parallel-plans.html", "label": "PostgreSQL 16.15 \u00b7 parallel-plans", "sha256": "53d83f63f97381fe1e4c0cfe5ceb81d30c1542b03e35a144684afd8fb3b9686c"}], "node_tag": "T_Group", "sections": [{"title": "EXPLAIN names and attributes", "paragraphs": ["Structured formats use the Node Type above. Text-format spellings can also include operation, strategy, join type, scan direction or aggregation-stage attributes.", "Text names recorded by this source: Group.", "Parallel-aware and parallel-safe are different plan properties. A node running inside a parallel worker is not necessarily a parallel-aware node."]}, {"title": "Memory and temporary storage", "paragraphs": ["This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider."]}, {"title": "Parallel execution and instrumentation", "paragraphs": ["The source callbacks below can coordinate execution or collect worker instrumentation. Their presence is not a blanket claim that this node supports a shared parallel scan or shared state.", "Callbacks in this build: none extracted from this node implementation."]}, {"title": "Same-version manual discussion", "paragraphs": ["PostgreSQL supports parallel aggregation by aggregating in two stages. First, each process participating in the parallel portion of the query performs an aggregation step, producing a partial result for each group of which that process is aware. This is reflected in the plan as a Partial Aggregate node. Second, the partial results are transferred to the leader via Gather or Gather Merge . Finally, the leader re-aggregates the results across all workers in order to produce the final result. This is reflected in the plan as a Finalize Aggregate node."]}, {"title": "Executor implementation notes", "paragraphs": ["nodeGroup.c Routines to handle group nodes (used for queries with GROUP BY clause).", "DESCRIPTION The Group node is designed for handling queries with a GROUP BY clause. Its outer plan must deliver tuples that are sorted in the order specified by the grouping columns (ie. tuples from the same group are consecutive). That way, we just have to compare adjacent tuples to locate group boundaries.", "The ScanTupleSlot holds the (copied) first tuple of each group.", "We need not call ResetExprContext here because ExecQualAndReset() will reset the per-tuple memory context once per input tuple.", "If first time through, acquire first input tuple and determine whether to return it or not."]}, {"code": "case T_Group:\n\t\t\tpname = sname = \"Group\";\n\t\t\tbreak;", "title": "EXPLAIN identity in core source"}], "strategies": [], "description": ["Groups an ordered input stream by its grouping columns."], "evidence_kind": "source and documentation", "explain_names": ["Group"], "partial_modes": [], "comparison_data": {"node_tag": "T_Group", "strategies": [], "text_names": ["Group"], "initializer": "ExecInitGroup", "partial_modes": [], "memory_mechanism": "unclassified", "parallel_callbacks": []}, "comparison_hash": "c75b880801aecfa8f510650c6bb3c2e0aa820810550fefe9c62d04727c0c0048", "explain_prefixes": ["Parallel", "Async"], "runtime_verified": false, "source_inventory": {"explain": "src/backend/commands/explain.c", "executor": "src/backend/executor/execProcnode.c", "implementation": "src/backend/executor/nodeGroup.c"}, "parallel_callbacks": []}, "17": {"facts": [{"label": "Core node tag", "value": "T_Group"}, {"label": "Structured EXPLAIN Node Type", "value": "Group"}, {"label": "Inputs", "value": "One ordered child plan"}, {"label": "Output", "value": "One tuple per group"}, {"label": "Executor initializer", "value": "ExecInitGroup"}, {"label": "Memory mechanism", "value": "unclassified"}], "memory": {"evidence": [{"url": "https://ftp.postgresql.org/pub/source/v17.11/postgresql-17.11.tar.bz2", "path": "src/backend/executor/nodeGroup.c", "label": "src/backend/executor/nodeGroup.c", "sha256": "4346791fa9c4150f00739013c9c36824076b9bb8cbe9aa04caf978d7cd461b99", "archive_sha256": "dd27f2b3c59e73ed14aa3324901242bf69a032a6347805f274e6260322d42979"}], "mechanism": "unclassified", "description": "This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider.", "source_notes": []}, "tables": [{"key": "explain-labels", "rows": [{"label": "Group", "identity": "Group"}], "title": "EXPLAIN labels in this source build", "columns": [{"key": "label", "label": "Text-format label"}, {"key": "identity", "label": "Structured node identity"}]}], "related": [{"url": "/wiki/sql/explain/?v=17", "label": "EXPLAIN"}, {"url": "/docs/17/using-explain.html", "label": "Using EXPLAIN"}, {"url": "/docs/17/parallel-plans.html", "label": "Parallel plans"}], "release": {"ref": "PostgreSQL 17.11 source archive", "label": "17.11", "major": "17", "channel": "stable", "revision": "dd27f2b3c59e73ed14aa3324901242bf69a032a6347805f274e6260322d42979", "source_url": "https://ftp.postgresql.org/pub/source/v17.11/postgresql-17.11.tar.bz2", "source_snapshot_utc": ""}, "sources": [{"url": "https://ftp.postgresql.org/pub/source/v17.11/postgresql-17.11.tar.bz2", "line": 1543, "path": "src/backend/commands/explain.c", "label": "src/backend/commands/explain.c:1543", "sha256": "741251b1a3b6d269a52a673d42eb63b02e13a5872db7b359b137086ab21b63c8", "archive_sha256": "dd27f2b3c59e73ed14aa3324901242bf69a032a6347805f274e6260322d42979"}, {"url": "https://ftp.postgresql.org/pub/source/v17.11/postgresql-17.11.tar.bz2", "line": 335, "path": "src/backend/executor/execProcnode.c", "label": "src/backend/executor/execProcnode.c:335", "sha256": "a77576e158b94cb01fa8c5174ba133004eabdd727660323f8afc66c8d2e757b8", "archive_sha256": "dd27f2b3c59e73ed14aa3324901242bf69a032a6347805f274e6260322d42979"}, {"url": "https://ftp.postgresql.org/pub/source/v17.11/postgresql-17.11.tar.bz2", "path": "src/backend/executor/nodeGroup.c", "label": "src/backend/executor/nodeGroup.c", "sha256": "4346791fa9c4150f00739013c9c36824076b9bb8cbe9aa04caf978d7cd461b99", "archive_sha256": "dd27f2b3c59e73ed14aa3324901242bf69a032a6347805f274e6260322d42979"}, {"url": "https://ftp.postgresql.org/pub/source/v17.11/postgresql-17.11.tar.bz2", "path": "src/include/nodes/plannodes.h", "label": "src/include/nodes/plannodes.h", "sha256": "d390dd69e2d3f5085beb42b33e46ff0676a2959b916a12b82118a7e545f8e562", "archive_sha256": "dd27f2b3c59e73ed14aa3324901242bf69a032a6347805f274e6260322d42979"}, {"url": "/docs/17/parallel-plans.html#PARALLEL-AGGREGATION", "path": "parallel-plans.html", "label": "PostgreSQL 17.11 \u00b7 parallel-plans", "sha256": "784fe3d3b7ae7d1a34e466aa551bde484a40a3b60dc5d2ada6e1675f40713bbc"}], "node_tag": "T_Group", "sections": [{"title": "EXPLAIN names and attributes", "paragraphs": ["Structured formats use the Node Type above. Text-format spellings can also include operation, strategy, join type, scan direction or aggregation-stage attributes.", "Text names recorded by this source: Group.", "Parallel-aware and parallel-safe are different plan properties. A node running inside a parallel worker is not necessarily a parallel-aware node."]}, {"title": "Memory and temporary storage", "paragraphs": ["This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider."]}, {"title": "Parallel execution and instrumentation", "paragraphs": ["The source callbacks below can coordinate execution or collect worker instrumentation. Their presence is not a blanket claim that this node supports a shared parallel scan or shared state.", "Callbacks in this build: none extracted from this node implementation."]}, {"title": "Same-version manual discussion", "paragraphs": ["PostgreSQL supports parallel aggregation by aggregating in two stages. First, each process participating in the parallel portion of the query performs an aggregation step, producing a partial result for each group of which that process is aware. This is reflected in the plan as a Partial Aggregate node. Second, the partial results are transferred to the leader via Gather or Gather Merge . Finally, the leader re-aggregates the results across all workers in order to produce the final result. This is reflected in the plan as a Finalize Aggregate node."]}, {"title": "Executor implementation notes", "paragraphs": ["nodeGroup.c Routines to handle group nodes (used for queries with GROUP BY clause).", "DESCRIPTION The Group node is designed for handling queries with a GROUP BY clause. Its outer plan must deliver tuples that are sorted in the order specified by the grouping columns (ie. tuples from the same group are consecutive). That way, we just have to compare adjacent tuples to locate group boundaries.", "The ScanTupleSlot holds the (copied) first tuple of each group.", "We need not call ResetExprContext here because ExecQualAndReset() will reset the per-tuple memory context once per input tuple.", "If first time through, acquire first input tuple and determine whether to return it or not."]}, {"code": "case T_Group:\n\t\t\tpname = sname = \"Group\";\n\t\t\tbreak;", "title": "EXPLAIN identity in core source"}], "strategies": [], "description": ["Groups an ordered input stream by its grouping columns."], "evidence_kind": "source and documentation", "explain_names": ["Group"], "partial_modes": [], "comparison_data": {"node_tag": "T_Group", "strategies": [], "text_names": ["Group"], "initializer": "ExecInitGroup", "partial_modes": [], "memory_mechanism": "unclassified", "parallel_callbacks": []}, "comparison_hash": "c75b880801aecfa8f510650c6bb3c2e0aa820810550fefe9c62d04727c0c0048", "explain_prefixes": ["Parallel", "Async"], "runtime_verified": false, "source_inventory": {"explain": "src/backend/commands/explain.c", "executor": "src/backend/executor/execProcnode.c", "implementation": "src/backend/executor/nodeGroup.c"}, "parallel_callbacks": []}, "18": {"facts": [{"label": "Core node tag", "value": "T_Group"}, {"label": "Structured EXPLAIN Node Type", "value": "Group"}, {"label": "Inputs", "value": "One ordered child plan"}, {"label": "Output", "value": "One tuple per group"}, {"label": "Executor initializer", "value": "ExecInitGroup"}, {"label": "Memory mechanism", "value": "unclassified"}], "memory": {"evidence": [{"url": "https://ftp.postgresql.org/pub/source/v18.6/postgresql-18.6.tar.bz2", "path": "src/backend/executor/nodeGroup.c", "label": "src/backend/executor/nodeGroup.c", "sha256": "c253c59d9928373ed62124342d5c314a4c52968a2fcc9399c39a3e1bab4fdbbf", "archive_sha256": "555610c24d53e4316da5b7d3fc25c279d96856d5e0e23ee308c328c5fa881d9f"}], "mechanism": "unclassified", "description": "This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider.", "source_notes": []}, "tables": [{"key": "explain-labels", "rows": [{"label": "Group", "identity": "Group"}], "title": "EXPLAIN labels in this source build", "columns": [{"key": "label", "label": "Text-format label"}, {"key": "identity", "label": "Structured node identity"}]}], "related": [{"url": "/wiki/sql/explain/?v=18", "label": "EXPLAIN"}, {"url": "/docs/18/using-explain.html", "label": "Using EXPLAIN"}, {"url": "/docs/18/parallel-plans.html", "label": "Parallel plans"}], "release": {"ref": "PostgreSQL 18.6 source archive", "label": "18.6", "major": "18", "channel": "stable", "revision": "555610c24d53e4316da5b7d3fc25c279d96856d5e0e23ee308c328c5fa881d9f", "source_url": "https://ftp.postgresql.org/pub/source/v18.6/postgresql-18.6.tar.bz2", "source_snapshot_utc": ""}, "sources": [{"url": "https://ftp.postgresql.org/pub/source/v18.6/postgresql-18.6.tar.bz2", "line": 1528, "path": "src/backend/commands/explain.c", "label": "src/backend/commands/explain.c:1528", "sha256": "34c86d6070224a0e981efef51f79101d6d505e5874f1684ace183034bab14bb4", "archive_sha256": "555610c24d53e4316da5b7d3fc25c279d96856d5e0e23ee308c328c5fa881d9f"}, {"url": "https://ftp.postgresql.org/pub/source/v18.6/postgresql-18.6.tar.bz2", "line": 335, "path": "src/backend/executor/execProcnode.c", "label": "src/backend/executor/execProcnode.c:335", "sha256": "f8a06a3f539077249b20664b2812433db6d7bd12b2c0ca633525db43d06f112a", "archive_sha256": "555610c24d53e4316da5b7d3fc25c279d96856d5e0e23ee308c328c5fa881d9f"}, {"url": "https://ftp.postgresql.org/pub/source/v18.6/postgresql-18.6.tar.bz2", "path": "src/backend/executor/nodeGroup.c", "label": "src/backend/executor/nodeGroup.c", "sha256": "c253c59d9928373ed62124342d5c314a4c52968a2fcc9399c39a3e1bab4fdbbf", "archive_sha256": "555610c24d53e4316da5b7d3fc25c279d96856d5e0e23ee308c328c5fa881d9f"}, {"url": "https://ftp.postgresql.org/pub/source/v18.6/postgresql-18.6.tar.bz2", "path": "src/include/nodes/plannodes.h", "label": "src/include/nodes/plannodes.h", "sha256": "52422b327a8049fbbb20d8b96008a0fc0a6fafa60f7eff3c695d5b2e83830120", "archive_sha256": "555610c24d53e4316da5b7d3fc25c279d96856d5e0e23ee308c328c5fa881d9f"}, {"url": "/docs/18/parallel-plans.html#PARALLEL-AGGREGATION", "path": "parallel-plans.html", "label": "PostgreSQL 18.6 \u00b7 parallel-plans", "sha256": "62207d207bead82b01b59dc119c4f95856f08655cc11d4699a05a40867ed2070"}], "node_tag": "T_Group", "sections": [{"title": "EXPLAIN names and attributes", "paragraphs": ["Structured formats use the Node Type above. Text-format spellings can also include operation, strategy, join type, scan direction or aggregation-stage attributes.", "Text names recorded by this source: Group.", "Parallel-aware and parallel-safe are different plan properties. A node running inside a parallel worker is not necessarily a parallel-aware node."]}, {"title": "Memory and temporary storage", "paragraphs": ["This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider."]}, {"title": "Parallel execution and instrumentation", "paragraphs": ["The source callbacks below can coordinate execution or collect worker instrumentation. Their presence is not a blanket claim that this node supports a shared parallel scan or shared state.", "Callbacks in this build: none extracted from this node implementation."]}, {"title": "Same-version manual discussion", "paragraphs": ["PostgreSQL supports parallel aggregation by aggregating in two stages. First, each process participating in the parallel portion of the query performs an aggregation step, producing a partial result for each group of which that process is aware. This is reflected in the plan as a Partial Aggregate node. Second, the partial results are transferred to the leader via Gather or Gather Merge . Finally, the leader re-aggregates the results across all workers in order to produce the final result. This is reflected in the plan as a Finalize Aggregate node."]}, {"title": "Executor implementation notes", "paragraphs": ["nodeGroup.c Routines to handle group nodes (used for queries with GROUP BY clause).", "DESCRIPTION The Group node is designed for handling queries with a GROUP BY clause. Its outer plan must deliver tuples that are sorted in the order specified by the grouping columns (ie. tuples from the same group are consecutive). That way, we just have to compare adjacent tuples to locate group boundaries.", "The ScanTupleSlot holds the (copied) first tuple of each group.", "We need not call ResetExprContext here because ExecQualAndReset() will reset the per-tuple memory context once per input tuple.", "If first time through, acquire first input tuple and determine whether to return it or not."]}, {"code": "case T_Group:\n\t\t\tpname = sname = \"Group\";\n\t\t\tbreak;", "title": "EXPLAIN identity in core source"}], "strategies": [], "description": ["Groups an ordered input stream by its grouping columns."], "evidence_kind": "source and documentation", "explain_names": ["Group"], "partial_modes": [], "comparison_data": {"node_tag": "T_Group", "strategies": [], "text_names": ["Group"], "initializer": "ExecInitGroup", "partial_modes": [], "memory_mechanism": "unclassified", "parallel_callbacks": []}, "comparison_hash": "c75b880801aecfa8f510650c6bb3c2e0aa820810550fefe9c62d04727c0c0048", "explain_prefixes": ["Parallel", "Async"], "runtime_verified": false, "source_inventory": {"explain": "src/backend/commands/explain.c", "executor": "src/backend/executor/execProcnode.c", "implementation": "src/backend/executor/nodeGroup.c"}, "parallel_callbacks": []}, "19": {"facts": [{"label": "Core node tag", "value": "T_Group"}, {"label": "Structured EXPLAIN Node Type", "value": "Group"}, {"label": "Inputs", "value": "One ordered child plan"}, {"label": "Output", "value": "One tuple per group"}, {"label": "Executor initializer", "value": "ExecInitGroup"}, {"label": "Memory mechanism", "value": "unclassified"}], "memory": {"evidence": [{"url": "https://ftp.postgresql.org/pub/source/v19beta4/postgresql-19beta4.tar.bz2", "path": "src/backend/executor/nodeGroup.c", "label": "src/backend/executor/nodeGroup.c", "sha256": "aeae380a5b5bb72fa98cb0725c37651fc1408f175089e82226c46de40a734fec", "archive_sha256": "83157ee9c599d03b2f7a3d73ef3a56ec24e0e79cc2b3501a64d1364f56398c86"}], "mechanism": "unclassified", "description": "This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider.", "source_notes": []}, "tables": [{"key": "explain-labels", "rows": [{"label": "Group", "identity": "Group"}], "title": "EXPLAIN labels in this source build", "columns": [{"key": "label", "label": "Text-format label"}, {"key": "identity", "label": "Structured node identity"}]}], "related": [{"url": "/wiki/sql/explain/?v=19", "label": "EXPLAIN"}, {"url": "/docs/19/using-explain.html", "label": "Using EXPLAIN"}, {"url": "/docs/19/parallel-plans.html", "label": "Parallel plans"}], "release": {"ref": "PostgreSQL 19beta4 source archive", "label": "19beta4", "major": "19", "channel": "preview", "revision": "83157ee9c599d03b2f7a3d73ef3a56ec24e0e79cc2b3501a64d1364f56398c86", "source_url": "https://ftp.postgresql.org/pub/source/v19beta4/postgresql-19beta4.tar.bz2", "source_snapshot_utc": ""}, "sources": [{"url": "https://ftp.postgresql.org/pub/source/v19beta4/postgresql-19beta4.tar.bz2", "line": 1540, "path": "src/backend/commands/explain.c", "label": "src/backend/commands/explain.c:1540", "sha256": "8b115b1c194a4b54ae630209a741e293b1df49a9052f10b2de9ca092a48998e3", "archive_sha256": "83157ee9c599d03b2f7a3d73ef3a56ec24e0e79cc2b3501a64d1364f56398c86"}, {"url": "https://ftp.postgresql.org/pub/source/v19beta4/postgresql-19beta4.tar.bz2", "line": 335, "path": "src/backend/executor/execProcnode.c", "label": "src/backend/executor/execProcnode.c:335", "sha256": "5e39b2037bed672da55104229ecc32da5abde44c26bcad01479edcfa044d09ed", "archive_sha256": "83157ee9c599d03b2f7a3d73ef3a56ec24e0e79cc2b3501a64d1364f56398c86"}, {"url": "https://ftp.postgresql.org/pub/source/v19beta4/postgresql-19beta4.tar.bz2", "path": "src/backend/executor/nodeGroup.c", "label": "src/backend/executor/nodeGroup.c", "sha256": "aeae380a5b5bb72fa98cb0725c37651fc1408f175089e82226c46de40a734fec", "archive_sha256": "83157ee9c599d03b2f7a3d73ef3a56ec24e0e79cc2b3501a64d1364f56398c86"}, {"url": "https://ftp.postgresql.org/pub/source/v19beta4/postgresql-19beta4.tar.bz2", "path": "src/include/nodes/plannodes.h", "label": "src/include/nodes/plannodes.h", "sha256": "1c65d5d6b6c81c71531685843647869bcae630779d815a5036b06e070c6c06c7", "archive_sha256": "83157ee9c599d03b2f7a3d73ef3a56ec24e0e79cc2b3501a64d1364f56398c86"}, {"url": "/docs/19/parallel-plans.html#PARALLEL-AGGREGATION", "path": "parallel-plans.html", "label": "PostgreSQL 19beta4 \u00b7 parallel-plans", "sha256": "f99fee3456a48a5ce2c399d6b35ab93183c2c9012e8ed60c53c0c253f79c3756"}], "node_tag": "T_Group", "sections": [{"title": "EXPLAIN names and attributes", "paragraphs": ["Structured formats use the Node Type above. Text-format spellings can also include operation, strategy, join type, scan direction or aggregation-stage attributes.", "Text names recorded by this source: Group.", "Parallel-aware and parallel-safe are different plan properties. A node running inside a parallel worker is not necessarily a parallel-aware node."]}, {"title": "Memory and temporary storage", "paragraphs": ["This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider."]}, {"title": "Parallel execution and instrumentation", "paragraphs": ["The source callbacks below can coordinate execution or collect worker instrumentation. Their presence is not a blanket claim that this node supports a shared parallel scan or shared state.", "Callbacks in this build: none extracted from this node implementation."]}, {"title": "Same-version manual discussion", "paragraphs": ["PostgreSQL supports parallel aggregation by aggregating in two stages. First, each process participating in the parallel portion of the query performs an aggregation step, producing a partial result for each group of which that process is aware. This is reflected in the plan as a Partial Aggregate node. Second, the partial results are transferred to the leader via Gather or Gather Merge . Finally, the leader re-aggregates the results across all workers in order to produce the final result. This is reflected in the plan as a Finalize Aggregate node."]}, {"title": "Executor implementation notes", "paragraphs": ["nodeGroup.c Routines to handle group nodes (used for queries with GROUP BY clause).", "DESCRIPTION The Group node is designed for handling queries with a GROUP BY clause. Its outer plan must deliver tuples that are sorted in the order specified by the grouping columns (ie. tuples from the same group are consecutive). That way, we just have to compare adjacent tuples to locate group boundaries.", "The ScanTupleSlot holds the (copied) first tuple of each group.", "We need not call ResetExprContext here because ExecQualAndReset() will reset the per-tuple memory context once per input tuple.", "If first time through, acquire first input tuple and determine whether to return it or not."]}, {"code": "case T_Group:\n\t\t\tpname = sname = \"Group\";\n\t\t\tbreak;", "title": "EXPLAIN identity in core source"}], "strategies": [], "description": ["Groups an ordered input stream by its grouping columns."], "evidence_kind": "source and documentation", "explain_names": ["Group"], "partial_modes": [], "comparison_data": {"node_tag": "T_Group", "strategies": [], "text_names": ["Group"], "initializer": "ExecInitGroup", "partial_modes": [], "memory_mechanism": "unclassified", "parallel_callbacks": []}, "comparison_hash": "c75b880801aecfa8f510650c6bb3c2e0aa820810550fefe9c62d04727c0c0048", "explain_prefixes": ["Parallel", "Async"], "runtime_verified": false, "source_inventory": {"explain": "src/backend/commands/explain.c", "executor": "src/backend/executor/execProcnode.c", "implementation": "src/backend/executor/nodeGroup.c"}, "parallel_callbacks": []}, "20": {"facts": [{"label": "Core node tag", "value": "T_Group"}, {"label": "Structured EXPLAIN Node Type", "value": "Group"}, {"label": "Inputs", "value": "One ordered child plan"}, {"label": "Output", "value": "One tuple per group"}, {"label": "Executor initializer", "value": "ExecInitGroup"}, {"label": "Memory mechanism", "value": "unclassified"}], "memory": {"evidence": [{"url": "https://ftp.postgresql.org/pub/snapshot/dev/postgresql-snapshot.tar.bz2", "path": "src/backend/executor/nodeGroup.c", "label": "src/backend/executor/nodeGroup.c", "sha256": "aeae380a5b5bb72fa98cb0725c37651fc1408f175089e82226c46de40a734fec", "archive_sha256": "4d3346909b201ac1648232cf290462a7070c119326f56196f1f0253ed80fae41"}], "mechanism": "unclassified", "description": "This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider.", "source_notes": []}, "tables": [{"key": "explain-labels", "rows": [{"label": "Group", "identity": "Group"}], "title": "EXPLAIN labels in this source build", "columns": [{"key": "label", "label": "Text-format label"}, {"key": "identity", "label": "Structured node identity"}]}], "related": [{"url": "/wiki/sql/explain/?v=20", "label": "EXPLAIN"}, {"url": "/docs/devel/using-explain.html", "label": "Using EXPLAIN"}, {"url": "/docs/devel/parallel-plans.html", "label": "Parallel plans"}], "release": {"ref": "PostgreSQL 20devel source archive", "label": "20devel", "major": "20", "channel": "devel", "revision": "4d3346909b201ac1648232cf290462a7070c119326f56196f1f0253ed80fae41", "source_url": "https://ftp.postgresql.org/pub/snapshot/dev/postgresql-snapshot.tar.bz2", "source_snapshot_utc": "26-Sep-2026 20:22"}, "sources": [{"url": "https://ftp.postgresql.org/pub/snapshot/dev/postgresql-snapshot.tar.bz2", "line": 1540, "path": "src/backend/commands/explain.c", "label": "src/backend/commands/explain.c:1540", "sha256": "13402758013520451539427b5993db06d463ca11c4e2d4cc5444e82367688077", "archive_sha256": "4d3346909b201ac1648232cf290462a7070c119326f56196f1f0253ed80fae41"}, {"url": "https://ftp.postgresql.org/pub/snapshot/dev/postgresql-snapshot.tar.bz2", "line": 335, "path": "src/backend/executor/execProcnode.c", "label": "src/backend/executor/execProcnode.c:335", "sha256": "5e39b2037bed672da55104229ecc32da5abde44c26bcad01479edcfa044d09ed", "archive_sha256": "4d3346909b201ac1648232cf290462a7070c119326f56196f1f0253ed80fae41"}, {"url": "https://ftp.postgresql.org/pub/snapshot/dev/postgresql-snapshot.tar.bz2", "path": "src/backend/executor/nodeGroup.c", "label": "src/backend/executor/nodeGroup.c", "sha256": "aeae380a5b5bb72fa98cb0725c37651fc1408f175089e82226c46de40a734fec", "archive_sha256": "4d3346909b201ac1648232cf290462a7070c119326f56196f1f0253ed80fae41"}, {"url": "https://ftp.postgresql.org/pub/snapshot/dev/postgresql-snapshot.tar.bz2", "path": "src/include/nodes/plannodes.h", "label": "src/include/nodes/plannodes.h", "sha256": "7a94ed1652f0d74d50c39971d1cd3e8051dbc0d6058f31b6de71a433ca343521", "archive_sha256": "4d3346909b201ac1648232cf290462a7070c119326f56196f1f0253ed80fae41"}, {"url": "/docs/devel/parallel-plans.html#PARALLEL-AGGREGATION", "path": "parallel-plans.html", "label": "PostgreSQL 20devel \u00b7 parallel-plans", "sha256": "6451d4254d26d789b8697ba7207288ac26e75e56f9711c8a5a3f5480171a4724"}], "node_tag": "T_Group", "sections": [{"title": "EXPLAIN names and attributes", "paragraphs": ["Structured formats use the Node Type above. Text-format spellings can also include operation, strategy, join type, scan direction or aggregation-stage attributes.", "Text names recorded by this source: Group.", "Parallel-aware and parallel-safe are different plan properties. A node running inside a parallel worker is not necessarily a parallel-aware node."]}, {"title": "Memory and temporary storage", "paragraphs": ["This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider."]}, {"title": "Parallel execution and instrumentation", "paragraphs": ["The source callbacks below can coordinate execution or collect worker instrumentation. Their presence is not a blanket claim that this node supports a shared parallel scan or shared state.", "Callbacks in this build: none extracted from this node implementation."]}, {"title": "Same-version manual discussion", "paragraphs": ["PostgreSQL supports parallel aggregation by aggregating in two stages. First, each process participating in the parallel portion of the query performs an aggregation step, producing a partial result for each group of which that process is aware. This is reflected in the plan as a Partial Aggregate node. Second, the partial results are transferred to the leader via Gather or Gather Merge . Finally, the leader re-aggregates the results across all workers in order to produce the final result. This is reflected in the plan as a Finalize Aggregate node."]}, {"title": "Executor implementation notes", "paragraphs": ["nodeGroup.c Routines to handle group nodes (used for queries with GROUP BY clause).", "DESCRIPTION The Group node is designed for handling queries with a GROUP BY clause. Its outer plan must deliver tuples that are sorted in the order specified by the grouping columns (ie. tuples from the same group are consecutive). That way, we just have to compare adjacent tuples to locate group boundaries.", "The ScanTupleSlot holds the (copied) first tuple of each group.", "We need not call ResetExprContext here because ExecQualAndReset() will reset the per-tuple memory context once per input tuple.", "If first time through, acquire first input tuple and determine whether to return it or not."]}, {"code": "case T_Group:\n\t\t\tpname = sname = \"Group\";\n\t\t\tbreak;", "title": "EXPLAIN identity in core source"}], "strategies": [], "description": ["Groups an ordered input stream by its grouping columns."], "evidence_kind": "source and documentation", "explain_names": ["Group"], "partial_modes": [], "comparison_data": {"node_tag": "T_Group", "strategies": [], "text_names": ["Group"], "initializer": "ExecInitGroup", "partial_modes": [], "memory_mechanism": "unclassified", "parallel_callbacks": []}, "comparison_hash": "c75b880801aecfa8f510650c6bb3c2e0aa820810550fefe9c62d04727c0c0048", "explain_prefixes": ["Parallel", "Async"], "runtime_verified": false, "source_inventory": {"explain": "src/backend/commands/explain.c", "executor": "src/backend/executor/execProcnode.c", "implementation": "src/backend/executor/nodeGroup.c"}, "parallel_callbacks": []}}}, "snapshot": {"facts": [{"label": "Core node tag", "value": "T_Group"}, {"label": "Structured EXPLAIN Node Type", "value": "Group"}, {"label": "Inputs", "value": "One ordered child plan"}, {"label": "Output", "value": "One tuple per group"}, {"label": "Executor initializer", "value": "ExecInitGroup"}, {"label": "Memory mechanism", "value": "unclassified"}], "memory": {"evidence": [{"url": "https://ftp.postgresql.org/pub/source/v18.6/postgresql-18.6.tar.bz2", "path": "src/backend/executor/nodeGroup.c", "label": "src/backend/executor/nodeGroup.c", "sha256": "c253c59d9928373ed62124342d5c314a4c52968a2fcc9399c39a3e1bab4fdbbf", "archive_sha256": "555610c24d53e4316da5b7d3fc25c279d96856d5e0e23ee308c328c5fa881d9f"}], "mechanism": "unclassified", "description": "This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider.", "source_notes": []}, "tables": [{"key": "explain-labels", "rows": [{"label": "Group", "identity": "Group"}], "title": "EXPLAIN labels in this source build", "columns": [{"key": "label", "label": "Text-format label"}, {"key": "identity", "label": "Structured node identity"}]}], "related": [{"url": "/wiki/sql/explain/?v=18", "label": "EXPLAIN"}, {"url": "/docs/18/using-explain.html", "label": "Using EXPLAIN"}, {"url": "/docs/18/parallel-plans.html", "label": "Parallel plans"}], "release": {"ref": "PostgreSQL 18.6 source archive", "label": "18.6", "major": "18", "channel": "stable", "revision": "555610c24d53e4316da5b7d3fc25c279d96856d5e0e23ee308c328c5fa881d9f", "source_url": "https://ftp.postgresql.org/pub/source/v18.6/postgresql-18.6.tar.bz2", "source_snapshot_utc": ""}, "sources": [{"url": "https://ftp.postgresql.org/pub/source/v18.6/postgresql-18.6.tar.bz2", "line": 1528, "path": "src/backend/commands/explain.c", "label": "src/backend/commands/explain.c:1528", "sha256": "34c86d6070224a0e981efef51f79101d6d505e5874f1684ace183034bab14bb4", "archive_sha256": "555610c24d53e4316da5b7d3fc25c279d96856d5e0e23ee308c328c5fa881d9f"}, {"url": "https://ftp.postgresql.org/pub/source/v18.6/postgresql-18.6.tar.bz2", "line": 335, "path": "src/backend/executor/execProcnode.c", "label": "src/backend/executor/execProcnode.c:335", "sha256": "f8a06a3f539077249b20664b2812433db6d7bd12b2c0ca633525db43d06f112a", "archive_sha256": "555610c24d53e4316da5b7d3fc25c279d96856d5e0e23ee308c328c5fa881d9f"}, {"url": "https://ftp.postgresql.org/pub/source/v18.6/postgresql-18.6.tar.bz2", "path": "src/backend/executor/nodeGroup.c", "label": "src/backend/executor/nodeGroup.c", "sha256": "c253c59d9928373ed62124342d5c314a4c52968a2fcc9399c39a3e1bab4fdbbf", "archive_sha256": "555610c24d53e4316da5b7d3fc25c279d96856d5e0e23ee308c328c5fa881d9f"}, {"url": "https://ftp.postgresql.org/pub/source/v18.6/postgresql-18.6.tar.bz2", "path": "src/include/nodes/plannodes.h", "label": "src/include/nodes/plannodes.h", "sha256": "52422b327a8049fbbb20d8b96008a0fc0a6fafa60f7eff3c695d5b2e83830120", "archive_sha256": "555610c24d53e4316da5b7d3fc25c279d96856d5e0e23ee308c328c5fa881d9f"}, {"url": "/docs/18/parallel-plans.html#PARALLEL-AGGREGATION", "path": "parallel-plans.html", "label": "PostgreSQL 18.6 \u00b7 parallel-plans", "sha256": "62207d207bead82b01b59dc119c4f95856f08655cc11d4699a05a40867ed2070"}], "node_tag": "T_Group", "sections": [{"title": "EXPLAIN names and attributes", "paragraphs": ["Structured formats use the Node Type above. Text-format spellings can also include operation, strategy, join type, scan direction or aggregation-stage attributes.", "Text names recorded by this source: Group.", "Parallel-aware and parallel-safe are different plan properties. A node running inside a parallel worker is not necessarily a parallel-aware node."]}, {"title": "Memory and temporary storage", "paragraphs": ["This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider."]}, {"title": "Parallel execution and instrumentation", "paragraphs": ["The source callbacks below can coordinate execution or collect worker instrumentation. Their presence is not a blanket claim that this node supports a shared parallel scan or shared state.", "Callbacks in this build: none extracted from this node implementation."]}, {"title": "Same-version manual discussion", "paragraphs": ["PostgreSQL supports parallel aggregation by aggregating in two stages. First, each process participating in the parallel portion of the query performs an aggregation step, producing a partial result for each group of which that process is aware. This is reflected in the plan as a Partial Aggregate node. Second, the partial results are transferred to the leader via Gather or Gather Merge . Finally, the leader re-aggregates the results across all workers in order to produce the final result. This is reflected in the plan as a Finalize Aggregate node."]}, {"title": "Executor implementation notes", "paragraphs": ["nodeGroup.c Routines to handle group nodes (used for queries with GROUP BY clause).", "DESCRIPTION The Group node is designed for handling queries with a GROUP BY clause. Its outer plan must deliver tuples that are sorted in the order specified by the grouping columns (ie. tuples from the same group are consecutive). That way, we just have to compare adjacent tuples to locate group boundaries.", "The ScanTupleSlot holds the (copied) first tuple of each group.", "We need not call ResetExprContext here because ExecQualAndReset() will reset the per-tuple memory context once per input tuple.", "If first time through, acquire first input tuple and determine whether to return it or not."]}, {"code": "case T_Group:\n\t\t\tpname = sname = \"Group\";\n\t\t\tbreak;", "title": "EXPLAIN identity in core source"}], "strategies": [], "description": ["Groups an ordered input stream by its grouping columns."], "evidence_kind": "source and documentation", "explain_names": ["Group"], "partial_modes": [], "comparison_data": {"node_tag": "T_Group", "strategies": [], "text_names": ["Group"], "initializer": "ExecInitGroup", "partial_modes": [], "memory_mechanism": "unclassified", "parallel_callbacks": []}, "comparison_hash": "c75b880801aecfa8f510650c6bb3c2e0aa820810550fefe9c62d04727c0c0048", "explain_prefixes": ["Parallel", "Async"], "runtime_verified": false, "source_inventory": {"explain": "src/backend/commands/explain.c", "executor": "src/backend/executor/execProcnode.c", "implementation": "src/backend/executor/nodeGroup.c"}, "parallel_callbacks": []}, "comparison": {"left": "17", "right": "18", "status": "unchanged", "diff": ""}}