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Minor refactoring in heap_page_prune 

Pass 'page', 'blockno' and 'maxoff' to heap_prune_chain() as
arguments, so that it doesn't need to fetch them from the buffer. This
saves a few cycles per chain.

Remove the "if (off_loc != NULL)" checks, and require the caller to
pass a non-NULL 'off_loc'. Pass a pointer to a dummy local variable
when it's not needed. Those checks are cheap, but it's still better to
avoid them in the per-chain loops when we can do so easily.

The CPU time saving from these changes are hardly measurable, but
fewer instructions is good anyway, so why not. I spotted the potential
for these while reviewing Melanie Plageman's patch set to combine
prune and freeze records.

Discussion: https://www.postgresql.org/message-id/CAAKRu_abm2tHhrc0QSQa%3D%3DsHe%3DVA1%3Doz1dJMQYUOKuHmu%2B9Xrg%40mail.gmail.com
This commit is contained in:
Heikki Linnakangas 2024-04-01 12:07:30 +03:00
parent f5a227895e
commit 9917e79d99
1 changed files with 15 additions and 22 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

37
src/backend/access/heap/pruneheap.c
View File

@ -57,10 +57,8 @@ typedef struct
static HTSV_Result heap_prune_satisfies_vacuum(PruneState *prstate,
HeapTuple tup,
Buffer buffer);
static int heap_prune_chain(Buffer buffer,
OffsetNumber rootoffnum,
int8 *htsv,
PruneState *prstate);
static int heap_prune_chain(Page page, BlockNumber blockno, OffsetNumber maxoff,
OffsetNumber rootoffnum, int8 *htsv, PruneState *prstate);
static void heap_prune_record_prunable(PruneState *prstate, TransactionId xid);
static void heap_prune_record_redirect(PruneState *prstate,
OffsetNumber offnum, OffsetNumber rdoffnum);
@ -145,6 +143,7 @@ heap_page_prune_opt(Relation relation, Buffer buffer)
*/
if (PageIsFull(page) || PageGetHeapFreeSpace(page) < minfree)
{
OffsetNumber dummy_off_loc;
PruneResult presult;
/*
@ -153,7 +152,7 @@ heap_page_prune_opt(Relation relation, Buffer buffer)
* that during on-access pruning with the current implementation.
*/
heap_page_prune(relation, buffer, vistest, false,
&presult, PRUNE_ON_ACCESS, NULL);
&presult, PRUNE_ON_ACCESS, &dummy_off_loc);
/*
* Report the number of tuples reclaimed to pgstats. This is
@ -296,8 +295,7 @@ heap_page_prune(Relation relation, Buffer buffer,
* Set the offset number so that we can display it along with any
* error that occurred while processing this tuple.
*/
if (off_loc)
*off_loc = offnum;
*off_loc = offnum;
presult->htsv[offnum] = heap_prune_satisfies_vacuum(&prstate, &tup,
buffer);
@ -315,8 +313,7 @@ heap_page_prune(Relation relation, Buffer buffer,
continue;
/* see preceding loop */
if (off_loc)
*off_loc = offnum;
*off_loc = offnum;
/* Nothing to do if slot is empty */
itemid = PageGetItemId(page, offnum);
@ -324,13 +321,12 @@ heap_page_prune(Relation relation, Buffer buffer,
continue;
/* Process this item or chain of items */
presult->ndeleted += heap_prune_chain(buffer, offnum,
presult->ndeleted += heap_prune_chain(page, blockno, maxoff, offnum,
presult->htsv, &prstate);
}
/* Clear the offset information once we have processed the given page. */
if (off_loc)
*off_loc = InvalidOffsetNumber;
*off_loc = InvalidOffsetNumber;
/* Any error while applying the changes is critical */
START_CRIT_SECTION();
@ -452,22 +448,20 @@ heap_prune_satisfies_vacuum(PruneState *prstate, HeapTuple tup, Buffer buffer)
* Returns the number of tuples (to be) deleted from the page.
*/
static int
heap_prune_chain(Buffer buffer, OffsetNumber rootoffnum,
int8 *htsv, PruneState *prstate)
heap_prune_chain(Page page, BlockNumber blockno, OffsetNumber maxoff,
OffsetNumber rootoffnum, int8 *htsv, PruneState *prstate)
{
int ndeleted = 0;
Page dp = (Page) BufferGetPage(buffer);
TransactionId priorXmax = InvalidTransactionId;
ItemId rootlp;
HeapTupleHeader htup;
OffsetNumber latestdead = InvalidOffsetNumber,
maxoff = PageGetMaxOffsetNumber(dp),
offnum;
OffsetNumber chainitems[MaxHeapTuplesPerPage];
int nchain = 0,
i;
rootlp = PageGetItemId(dp, rootoffnum);
rootlp = PageGetItemId(page, rootoffnum);
/*
* If it's a heap-only tuple, then it is not the start of a HOT chain.
@ -475,7 +469,7 @@ heap_prune_chain(Buffer buffer, OffsetNumber rootoffnum,
if (ItemIdIsNormal(rootlp))
{
Assert(htsv[rootoffnum] != -1);
htup = (HeapTupleHeader) PageGetItem(dp, rootlp);
htup = (HeapTupleHeader) PageGetItem(page, rootlp);
if (HeapTupleHeaderIsHeapOnly(htup))
{
@ -536,7 +530,7 @@ heap_prune_chain(Buffer buffer, OffsetNumber rootoffnum,
if (prstate->marked[offnum])
break;
lp = PageGetItemId(dp, offnum);
lp = PageGetItemId(page, offnum);
/* Unused item obviously isn't part of the chain */
if (!ItemIdIsUsed(lp))
@ -575,7 +569,7 @@ heap_prune_chain(Buffer buffer, OffsetNumber rootoffnum,
}
Assert(ItemIdIsNormal(lp));
htup = (HeapTupleHeader) PageGetItem(dp, lp);
htup = (HeapTupleHeader) PageGetItem(page, lp);
/*
* Check the tuple XMIN against prior XMAX, if any
@ -666,8 +660,7 @@ heap_prune_chain(Buffer buffer, OffsetNumber rootoffnum,
/*
* Advance to next chain member.
*/
Assert(ItemPointerGetBlockNumber(&htup->t_ctid) ==
BufferGetBlockNumber(buffer));
Assert(ItemPointerGetBlockNumber(&htup->t_ctid) == blockno);
offnum = ItemPointerGetOffsetNumber(&htup->t_ctid);
priorXmax = HeapTupleHeaderGetUpdateXid(htup);
}