upstream/postgresql
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2026-04-15 22:10:45 -04:00
Code Issues Projects Releases Packages Wiki Activity Actions

heapam: Track heap block in IndexFetchHeapData.

Browse source 
Add an explicit BlockNumber field (xs_blk) to IndexFetchHeapData that
tracks which heap block is currently pinned in xs_cbuf.

heapam_index_fetch_tuple now uses xs_blk to determine when buffer
switching is needed, replacing the previous approach that compared
buffer identities via ReleaseAndReadBuffer on every non-HOT-chain call.

This is preparatory work for an upcoming commit that will add index
prefetching using a read stream.  Delegating the release of a currently
pinned buffer to ReleaseAndReadBuffer won't work anymore -- at least not
when the next buffer that the scan needs to pin is one returned by
read_stream_next_buffer (not a buffer returned by ReadBuffer).

Author: Peter Geoghegan <pg@bowt.ie>
Reviewed-By: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/CAH2-Wz=g=JTSyDB4UtB5su2ZcvsS7VbP+ZMvvaG6ABoCb+s8Lw@mail.gmail.com
This commit is contained in:
Peter Geoghegan 2026-04-04 11:45:33 -04:00
parent a29fdd6c8d
commit c7d09595e4
2 changed files with 22 additions and 14 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

31
src/backend/access/heap/heapam_indexscan.c
View file

@ -32,6 +32,7 @@ heapam_index_fetch_begin(Relation rel, uint32 flags)
hscan->xs_base.rel = rel;
hscan->xs_base.flags = flags;
hscan->xs_cbuf = InvalidBuffer;
hscan->xs_blk = InvalidBlockNumber;
hscan->xs_vmbuffer = InvalidBuffer;
return &hscan->xs_base;
@ -46,6 +47,7 @@ heapam_index_fetch_reset(IndexFetchTableData *scan)
{
ReleaseBuffer(hscan->xs_cbuf);
hscan->xs_cbuf = InvalidBuffer;
hscan->xs_blk = InvalidBlockNumber;
}
if (BufferIsValid(hscan->xs_vmbuffer))
@ -240,25 +242,30 @@ heapam_index_fetch_tuple(struct IndexFetchTableData *scan,
Assert(TTS_IS_BUFFERTUPLE(slot));
/* We can skip the buffer-switching logic if we're in mid-HOT chain. */
if (!*heap_continue)
/* We can skip the buffer-switching logic if we're on the same page. */
if (hscan->xs_blk != ItemPointerGetBlockNumber(tid))
{
/* Switch to correct buffer if we don't have it already */
Buffer prev_buf = hscan->xs_cbuf;
Assert(!*heap_continue);
hscan->xs_cbuf = ReleaseAndReadBuffer(hscan->xs_cbuf,
hscan->xs_base.rel,
ItemPointerGetBlockNumber(tid));
/* Remember this buffer's block number for next time */
hscan->xs_blk = ItemPointerGetBlockNumber(tid);
if (BufferIsValid(hscan->xs_cbuf))
ReleaseBuffer(hscan->xs_cbuf);
hscan->xs_cbuf = ReadBuffer(hscan->xs_base.rel, hscan->xs_blk);
/*
* Prune page, but only if we weren't already on this page
* Prune page when it is pinned for the first time
*/
if (prev_buf != hscan->xs_cbuf)
heap_page_prune_opt(hscan->xs_base.rel, hscan->xs_cbuf,
&hscan->xs_vmbuffer,
hscan->xs_base.flags & SO_HINT_REL_READ_ONLY);
heap_page_prune_opt(hscan->xs_base.rel, hscan->xs_cbuf,
&hscan->xs_vmbuffer,
hscan->xs_base.flags & SO_HINT_REL_READ_ONLY);
}
Assert(BufferGetBlockNumber(hscan->xs_cbuf) == hscan->xs_blk);
Assert(hscan->xs_blk == ItemPointerGetBlockNumber(tid));
/* Obtain share-lock on the buffer so we can examine visibility */
LockBuffer(hscan->xs_cbuf, BUFFER_LOCK_SHARE);
got_heap_tuple = heap_hot_search_buffer(tid,

5
src/include/access/heapam.h
View file

@ -122,10 +122,11 @@ typedef struct IndexFetchHeapData
IndexFetchTableData xs_base; /* AM independent part of the descriptor */
/*
* Current heap buffer in scan, if any. NB: if xs_cbuf is not
* InvalidBuffer, we hold a pin on that buffer.
* Current heap buffer in scan (and its block number), if any. NB: if
* xs_blk is not InvalidBlockNumber, we hold a pin in xs_cbuf.
*/
Buffer xs_cbuf;
BlockNumber xs_blk;
/* Current heap block's corresponding page in the visibility map */
Buffer xs_vmbuffer;