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baseStorage StructuresWikiStorage Structures · PGDATA pathsSubdirectory containing per-database subdirectories PGDATA paths $PGDATA/base Relative path base current_logfilesStorage StructuresWikiStorage Structures · PGDATA pathsFile recording the log file(s) currently written to by the logging collector PGDATA paths $PGDATA/current_logfiles Relative path current_logfiles Database File LayoutStorage StructuresWikiStorage Structures · Physical structuresThis section describes the storage format at the level of files and directories. Physical structures Definition scope Same-version core physical storage documentation Contents of PGDATA PG_… Database Page LayoutStorage StructuresWikiStorage Structures · Physical structuresThis section provides an overview of the page format used within PostgreSQL tables and indexes. [20] Sequences and TOAST tables are formatted just like a regular table. Physical structures … Free Space MapStorage StructuresWikiStorage Structures · Physical structuresEach heap and index relation, except for hash indexes, has a Free Space Map ( FSM ) to keep track of available space in the relation. It's stored alongside the main relation data in a separa… fsm forkStorage StructuresWikiStorage Structures · Relation forksEach table and index is stored in a separate file. For ordinary relations, these files are named after the table or index's filenode number, which can be found in pg_class . relfilenode . Bu… globalStorage StructuresWikiStorage Structures · PGDATA pathsSubdirectory containing cluster-wide tables, such as pg_database PGDATA paths $PGDATA/global Relative path global Heap-Only Tuples ( HOT )Storage StructuresWikiStorage Structures · Physical structuresTo allow for high concurrency, PostgreSQL uses multiversion concurrency control ( MVCC ) to store rows. However, MVCC has some downsides for update queries. Specifically, updates require new… init forkStorage StructuresWikiStorage Structures · Relation forksEach table and index is stored in a separate file. For ordinary relations, these files are named after the table or index's filenode number, which can be found in pg_class . relfilenode . Bu… main forkStorage StructuresWikiStorage Structures · Relation forksEach table and index is stored in a separate file. For ordinary relations, these files are named after the table or index's filenode number, which can be found in pg_class . relfilenode . Bu… pg_commit_tsStorage StructuresWikiStorage Structures · PGDATA pathsSubdirectory containing transaction commit timestamp data PGDATA paths $PGDATA/pg_commit_ts Relative path pg_commit_ts pg_dynshmemStorage StructuresWikiStorage Structures · PGDATA pathsSubdirectory containing files used by the dynamic shared memory subsystem PGDATA paths $PGDATA/pg_dynshmem Relative path pg_dynshmem pg_logicalStorage StructuresWikiStorage Structures · PGDATA pathsSubdirectory containing status data for logical decoding PGDATA paths $PGDATA/pg_logical Relative path pg_logical pg_multixactStorage StructuresWikiStorage Structures · PGDATA pathsSubdirectory containing multitransaction status data (used for shared row locks) PGDATA paths $PGDATA/pg_multixact Relative path pg_multixact pg_notifyStorage StructuresWikiStorage Structures · PGDATA pathsSubdirectory containing LISTEN/NOTIFY status data PGDATA paths $PGDATA/pg_notify Relative path pg_notify pg_replslotStorage StructuresWikiStorage Structures · PGDATA pathsSubdirectory containing replication slot data PGDATA paths $PGDATA/pg_replslot Relative path pg_replslot pg_serialStorage StructuresWikiStorage Structures · PGDATA pathsSubdirectory containing information about committed serializable transactions PGDATA paths $PGDATA/pg_serial Relative path pg_serial pg_snapshotsStorage StructuresWikiStorage Structures · PGDATA pathsSubdirectory containing exported snapshots PGDATA paths $PGDATA/pg_snapshots Relative path pg_snapshots pg_statStorage StructuresWikiStorage Structures · PGDATA pathsSubdirectory containing permanent files for the statistics subsystem PGDATA paths $PGDATA/pg_stat Relative path pg_stat pg_stat_tmpStorage StructuresWikiStorage Structures · PGDATA pathsSubdirectory containing temporary files for the statistics subsystem PGDATA paths $PGDATA/pg_stat_tmp Relative path pg_stat_tmp pg_subtransStorage StructuresWikiStorage Structures · PGDATA pathsSubdirectory containing subtransaction status data PGDATA paths $PGDATA/pg_subtrans Relative path pg_subtrans pg_tblspcStorage StructuresWikiStorage Structures · PGDATA pathsSubdirectory containing symbolic links to tablespaces PGDATA paths $PGDATA/pg_tblspc Relative path pg_tblspc pg_twophaseStorage StructuresWikiStorage Structures · PGDATA pathsSubdirectory containing state files for prepared transactions PGDATA paths $PGDATA/pg_twophase Relative path pg_twophase PG_VERSIONStorage StructuresWikiStorage Structures · PGDATA pathsA file containing the major version number of PostgreSQL PGDATA paths $PGDATA/PG_VERSION Relative path PG_VERSION pg_walStorage StructuresWikiStorage Structures · PGDATA pathsSubdirectory containing WAL (Write Ahead Log) files PGDATA paths $PGDATA/pg_wal Relative path pg_wal pg_xactStorage StructuresWikiStorage Structures · PGDATA pathsSubdirectory containing transaction commit status data PGDATA paths $PGDATA/pg_xact Relative path pg_xact postgresql.auto.confStorage StructuresWikiStorage Structures · PGDATA pathsA file used for storing configuration parameters that are set by ALTER SYSTEM PGDATA paths $PGDATA/postgresql.auto.conf Relative path postgresql.auto.conf postmaster.optsStorage StructuresWikiStorage Structures · PGDATA pathsA file recording the command-line options the server was last started with PGDATA paths $PGDATA/postmaster.opts Relative path postmaster.opts postmaster.pidStorage StructuresWikiStorage Structures · PGDATA pathsA lock file recording the current postmaster process ID (PID), cluster data directory path, postmaster start timestamp, port number, Unix-domain socket directory path (could be empty), first… Table row layoutStorage StructuresWikiStorage Structures · Physical structuresPhysical row headers, null bitmap, alignment and column data. Physical structures HeapTupleHeaderData Layout t_xmin TransactionId 4 bytes insert XID stamp t_xmax TransactionId 4 bytes delet… The Initialization ForkStorage StructuresWikiStorage Structures · Physical structuresEach unlogged table, and each index on an unlogged table, has an initialization fork. The initialization fork is an empty table or index of the appropriate type. When an unlogged table must … TOASTStorage StructuresWikiStorage Structures · Physical structuresThis section provides an overview of TOAST (The Oversized-Attribute Storage Technique). Physical structures Definition scope Same-version core physical storage documentation Visibility MapStorage StructuresWikiStorage Structures · Physical structuresEach heap relation has a Visibility Map (VM) to keep track of which pages contain only tuples that are known to be visible to all active transactions; it also keeps track of which pages cont… vm forkStorage StructuresWikiStorage Structures · Relation forksEach table and index is stored in a separate file. For ordinary relations, these files are named after the table or index's filenode number, which can be found in pg_class . relfilenode . Bu… WAL InternalsStorage StructuresWikiStorage Structures · Physical structuresWAL is automatically enabled; no action is required from the administrator except ensuring that the disk-space requirements for the WAL files are met, and that any necessary tuning is done (…