WorkTable Scan

Description

Reads the current working table of a recursive union.

Core node tag

T_WorkTableScan

Structured EXPLAIN Node Type

WorkTable Scan

Inputs

The recursive query working table

Output

Working-table tuples

Executor initializer

ExecInitWorkTableScan

Memory mechanism

unclassified

EXPLAIN names and attributes

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: WorkTable Scan.

Parallel-aware and parallel-safe are different plan properties. A node running inside a parallel worker is not necessarily a parallel-aware node.

Memory and temporary storage

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.

Parallel execution and instrumentation

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.

Executor implementation notes

Note: we intentionally do not support backward scan. Although it would take only a couple more lines here, it would force nodeRecursiveunion.c to create the tuplestore with backward scan enabled, which has a performance cost. In practice backward scan is never useful for a worktable plan node, since it cannot appear high enough in the plan tree of a scrollable cursor to be exposed to a backward-scan requirement. So it's not worth expending effort to support it.

Note: we are also assuming that this node is the only reader of the worktable. Therefore, we don't need a private read pointer for the tuplestore, nor do we need to tell tuplestore_gettupleslot to copy.

Get the next tuple from tuplestore. Return NULL if no more tuples.

WorkTableScanRecheck -- access method routine to recheck a tuple in EvalPlanQual

Scans the worktable sequentially and returns the next qualifying tuple. We call the ExecScan() routine and pass it the appropriate access method functions.

EXPLAIN identity in core source

case T_WorkTableScan:
			pname = sname = "WorkTable Scan";
			break;

Related entries

• EXPLAIN
• Using EXPLAIN
• Parallel plans

Documentation and source

• src/backend/commands/explain.c:1480
• src/backend/executor/execProcnode.c:279
• src/backend/executor/nodeWorktablescan.c
• src/include/nodes/plannodes.h

Compare versions

PostgreSQL 17 → 18: unchanged.

Compares recorded interfaces and attributes. Source fingerprints and build metadata are excluded; an absent sample is not proof of the introduction or removal release.

Related entries

• Bitmap Heap ScanBitmapHeapScan
• CTE ScanCteScan
• Function ScanFunctionScan
• Index Only ScanIndexOnlyScan
• Index ScanIndexScan
• Named Tuplestore ScanNamedTuplestoreScan
• Sample ScanSampleScan
• Seq ScanSeqScan
• Subquery ScanSubqueryScan
• Table Function ScanTableFuncScan
• Tid Range ScanTidRangeScan
• Tid ScanTidScan