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Allocate separate DSM chunk for parallel Index[Only]Scan instrumentation

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Previously, parallel index and index-only scans packed the parallel scan
descriptor and shared instrumentation (for EXPLAIN ANALYZE) into a
single DSM allocation. Since scans may be instrumented without being
parallel-aware, and vice versa, using separate DSM chunks -- each with
its own TOC key -- is cleaner. A future commit will extend this pattern
to other scan node types.

Author: Melanie Plageman <melanieplageman@gmail.com>
Reviewed-by: Tomas Vondra <tomas@vondra.me>
Discussion: https://postgr.es/m/flat/a177a6dd-240b-455a-8f25-aca0b1c08c6e%40vondra.me
This commit is contained in:
Melanie Plageman
2026-04-06 19:10:19 -04:00
parent 43222b8e53
commit dd78e69cfc
10 changed files with 202 additions and 154 deletions
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7
src/include/access/genam.h
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@@ -171,14 +171,9 @@ extern void index_endscan(IndexScanDesc scan);
extern void index_markpos(IndexScanDesc scan);
extern void index_restrpos(IndexScanDesc scan);
extern Size index_parallelscan_estimate(Relation indexRelation,
int nkeys, int norderbys, Snapshot snapshot,
bool instrument, bool parallel_aware,
int nworkers);
int nkeys, int norderbys, Snapshot snapshot);
extern void index_parallelscan_initialize(Relation heapRelation,
Relation indexRelation, Snapshot snapshot,
bool instrument, bool parallel_aware,
int nworkers,
SharedIndexScanInstrumentation **sharedinfo,
ParallelIndexScanDesc target);
extern void index_parallelrescan(IndexScanDesc scan);
extern IndexScanDesc index_beginscan_parallel(Relation heaprel,

1
src/include/access/relscan.h
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@@ -203,7 +203,6 @@ typedef struct ParallelIndexScanDescData
{
RelFileLocator ps_locator; /* physical table relation to scan */
RelFileLocator ps_indexlocator; /* physical index relation to scan */
Size ps_offset_ins; /* Offset to SharedIndexScanInstrumentation */
Size ps_offset_am; /* Offset to am-specific structure */
char ps_snapshot_data[FLEXIBLE_ARRAY_MEMBER];
} ParallelIndexScanDescData;

8
src/include/executor/instrument_node.h
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@@ -18,6 +18,14 @@
#ifndef INSTRUMENT_NODE_H
#define INSTRUMENT_NODE_H
/*
* Offset added to plan_node_id to create a second TOC key for per-worker scan
* instrumentation. Instrumentation and parallel-awareness are independent, so
* separate DSM chunks let each be allocated and initialized only when needed.
* In the future, if nodes need more DSM allocations, we would need a more
* robust system.
*/
#define PARALLEL_KEY_SCAN_INSTRUMENT_OFFSET UINT64CONST(0xD000000000000000)
/* ---------------------
* Instrumentation information for aggregate function execution

6
src/include/executor/nodeIndexonlyscan.h
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@@ -32,6 +32,12 @@ extern void ExecIndexOnlyScanReInitializeDSM(IndexOnlyScanState *node,
ParallelContext *pcxt);
extern void ExecIndexOnlyScanInitializeWorker(IndexOnlyScanState *node,
ParallelWorkerContext *pwcxt);
extern void ExecIndexOnlyScanInstrumentEstimate(IndexOnlyScanState *node,
ParallelContext *pcxt);
extern void ExecIndexOnlyScanInstrumentInitDSM(IndexOnlyScanState *node,
ParallelContext *pcxt);
extern void ExecIndexOnlyScanInstrumentInitWorker(IndexOnlyScanState *node,
ParallelWorkerContext *pwcxt);
extern void ExecIndexOnlyScanRetrieveInstrumentation(IndexOnlyScanState *node);
#endif /* NODEINDEXONLYSCAN_H */

6
src/include/executor/nodeIndexscan.h
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@@ -28,6 +28,12 @@ extern void ExecIndexScanInitializeDSM(IndexScanState *node, ParallelContext *pc
extern void ExecIndexScanReInitializeDSM(IndexScanState *node, ParallelContext *pcxt);
extern void ExecIndexScanInitializeWorker(IndexScanState *node,
ParallelWorkerContext *pwcxt);
extern void ExecIndexScanInstrumentEstimate(IndexScanState *node,
ParallelContext *pcxt);
extern void ExecIndexScanInstrumentInitDSM(IndexScanState *node,
ParallelContext *pcxt);
extern void ExecIndexScanInstrumentInitWorker(IndexScanState *node,
ParallelWorkerContext *pwcxt);
extern void ExecIndexScanRetrieveInstrumentation(IndexScanState *node);
/*