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help / color / mirror / Atom feedFrom: Nathan Bossart <[email protected]>
Subject: [PATCH v1 7/8] convert ParallelBlockTableScanDescData->phs_{start,num}block to atomics
Date: Thu, 9 Jul 2026 15:21:13 -0500
---
src/backend/access/heap/heapam_handler.c | 2 +-
src/backend/access/table/tableam.c | 59 +++++++++++-------------
src/include/access/relscan.h | 8 ++--
3 files changed, 31 insertions(+), 38 deletions(-)
diff --git a/src/backend/access/heap/heapam_handler.c b/src/backend/access/heap/heapam_handler.c
index bf87430cf01..0f24a132564 100644
--- a/src/backend/access/heap/heapam_handler.c
+++ b/src/backend/access/heap/heapam_handler.c
@@ -1965,7 +1965,7 @@ heapam_scan_get_blocks_done(HeapScanDesc hscan)
if (hscan->rs_base.rs_parallel != NULL)
{
bpscan = (ParallelBlockTableScanDesc) hscan->rs_base.rs_parallel;
- startblock = bpscan->phs_startblock;
+ startblock = pg_atomic_read_u32(&bpscan->phs_startblock);
}
else
startblock = hscan->rs_startblock;
diff --git a/src/backend/access/table/tableam.c b/src/backend/access/table/tableam.c
index 68ff0966f1c..f2038ea9205 100644
--- a/src/backend/access/table/tableam.c
+++ b/src/backend/access/table/tableam.c
@@ -421,9 +421,8 @@ table_block_parallelscan_initialize(Relation rel, ParallelTableScanDesc pscan)
bpscan->base.phs_syncscan = synchronize_seqscans &&
!RelationUsesLocalBuffers(rel) &&
bpscan->phs_nblocks > NBuffers / 4;
- SpinLockInit(&bpscan->phs_mutex);
- bpscan->phs_startblock = InvalidBlockNumber;
- bpscan->phs_numblock = InvalidBlockNumber;
+ pg_atomic_init_u32(&bpscan->phs_startblock, InvalidBlockNumber);
+ pg_atomic_init_u32(&bpscan->phs_numblock, InvalidBlockNumber);
pg_atomic_init_u64(&bpscan->phs_nallocated, 0);
return sizeof(ParallelBlockTableScanDescData);
@@ -459,25 +458,22 @@ table_block_parallelscan_startblock_init(Relation rel,
StaticAssertDecl(MaxBlockNumber <= 0xFFFFFFFE,
"pg_nextpower2_32 may be too small for non-standard BlockNumber width");
- BlockNumber sync_startpage = InvalidBlockNumber;
BlockNumber scan_nblocks;
/* Reset the state we use for controlling allocation size. */
memset(pbscanwork, 0, sizeof(*pbscanwork));
-retry:
- /* Grab the spinlock. */
- SpinLockAcquire(&pbscan->phs_mutex);
-
/*
* When the caller specified a limit on the number of blocks to scan, set
* that in the ParallelBlockTableScanDesc, if it's not been done by
* another worker already.
*/
- if (numblocks != InvalidBlockNumber &&
- pbscan->phs_numblock == InvalidBlockNumber)
+ if (numblocks != InvalidBlockNumber)
{
- pbscan->phs_numblock = numblocks;
+ uint32 expected = InvalidBlockNumber;
+
+ pg_atomic_compare_exchange_u32(&pbscan->phs_numblock, &expected,
+ numblocks);
}
/*
@@ -485,36 +481,35 @@ retry:
* so now. If a startblock was specified, start there, otherwise if this
* is not a synchronized scan, we just start at block 0, but if it is a
* synchronized scan, we must get the starting position from the
- * synchronized scan machinery. We can't hold the spinlock while doing
- * that, though, so release the spinlock, get the information we need, and
- * retry. If nobody else has initialized the scan in the meantime, we'll
- * fill in the value we fetched on the second time through.
+ * synchronized scan machinery.
+ *
+ * If another worker initializes phs_startblock concurrently, just use
+ * their value.
*/
- if (pbscan->phs_startblock == InvalidBlockNumber)
+ if (pg_atomic_read_u32(&pbscan->phs_startblock) == InvalidBlockNumber)
{
+ BlockNumber newstartblock;
+ uint32 expected = InvalidBlockNumber;
+
if (startblock != InvalidBlockNumber)
- pbscan->phs_startblock = startblock;
+ newstartblock = startblock;
else if (!pbscan->base.phs_syncscan)
- pbscan->phs_startblock = 0;
- else if (sync_startpage != InvalidBlockNumber)
- pbscan->phs_startblock = sync_startpage;
+ newstartblock = 0;
else
- {
- SpinLockRelease(&pbscan->phs_mutex);
- sync_startpage = ss_get_location(rel, pbscan->phs_nblocks);
- goto retry;
- }
+ newstartblock = ss_get_location(rel, pbscan->phs_nblocks);
+
+ pg_atomic_compare_exchange_u32(&pbscan->phs_startblock, &expected,
+ newstartblock);
}
- SpinLockRelease(&pbscan->phs_mutex);
/*
* Figure out how many blocks we're going to scan; either all of them, or
* just phs_numblock's worth, if a limit has been imposed.
*/
- if (pbscan->phs_numblock == InvalidBlockNumber)
+ if (pg_atomic_read_u32(&pbscan->phs_numblock) == InvalidBlockNumber)
scan_nblocks = pbscan->phs_nblocks;
else
- scan_nblocks = pbscan->phs_numblock;
+ scan_nblocks = pg_atomic_read_u32(&pbscan->phs_numblock);
/*
* We determine the chunk size based on scan_nblocks. First we split
@@ -595,10 +590,10 @@ table_block_parallelscan_nextpage(Relation rel,
*/
/* First, figure out how many blocks we're planning on scanning */
- if (pbscan->phs_numblock == InvalidBlockNumber)
+ if (pg_atomic_read_u32(&pbscan->phs_numblock) == InvalidBlockNumber)
scan_nblocks = pbscan->phs_nblocks;
else
- scan_nblocks = pbscan->phs_numblock;
+ scan_nblocks = pg_atomic_read_u32(&pbscan->phs_numblock);
/*
* Now check if we have any remaining blocks in a previous chunk for this
@@ -644,7 +639,7 @@ table_block_parallelscan_nextpage(Relation rel,
if (nallocated >= scan_nblocks)
page = InvalidBlockNumber; /* all blocks have been allocated */
else
- page = (nallocated + pbscan->phs_startblock) % pbscan->phs_nblocks;
+ page = (nallocated + pg_atomic_read_u32(&pbscan->phs_startblock)) % pbscan->phs_nblocks;
/*
* Report scan location. Normally, we report the current page number.
@@ -658,7 +653,7 @@ table_block_parallelscan_nextpage(Relation rel,
if (page != InvalidBlockNumber)
ss_report_location(rel, page);
else if (nallocated == pbscan->phs_nblocks)
- ss_report_location(rel, pbscan->phs_startblock);
+ ss_report_location(rel, pg_atomic_read_u32(&pbscan->phs_startblock));
}
return page;
diff --git a/src/include/access/relscan.h b/src/include/access/relscan.h
index 2ea06a67a63..2305d0159f3 100644
--- a/src/include/access/relscan.h
+++ b/src/include/access/relscan.h
@@ -19,7 +19,6 @@
#include "nodes/tidbitmap.h"
#include "port/atomics.h"
#include "storage/relfilelocator.h"
-#include "storage/spin.h"
#include "utils/relcache.h"
@@ -99,10 +98,9 @@ typedef struct ParallelBlockTableScanDescData
ParallelTableScanDescData base;
BlockNumber phs_nblocks; /* # blocks in relation at start of scan */
- slock_t phs_mutex; /* mutual exclusion for setting startblock */
- BlockNumber phs_startblock; /* starting block number */
- BlockNumber phs_numblock; /* # blocks to scan, or InvalidBlockNumber if
- * no limit */
+ pg_atomic_uint32 phs_startblock; /* starting block number */
+ pg_atomic_uint32 phs_numblock; /* # blocks to scan, or InvalidBlockNumber
+ * if no limit */
pg_atomic_uint64 phs_nallocated; /* number of blocks allocated to
* workers so far. */
} ParallelBlockTableScanDescData;
--
2.50.1 (Apple Git-155)
--Ot5x3ffkWEuxilWO
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
filename=v1-0008-convert-FastPathStrongRelationLocks-to-atomics.patch
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