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Remove retry loop in heap_page_prune().

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The retry loop is needed because heap_page_prune() calls
HeapTupleSatisfiesVacuum() and then lazy_scan_prune() does the same
thing again, and they might get different answers due to concurrent
clog updates.  But this patch makes heap_page_prune() return the
HeapTupleSatisfiesVacuum() results that it computed back to the
caller, which allows lazy_scan_prune() to avoid needing to recompute
those values in the first place. That's nice both because it eliminates
the need for a retry loop and also because it's cheaper.

Melanie Plageman, reviewed by David Geier, Andres Freund, and me.

Discussion: https://postgr.es/m/CAAKRu_br124qsGJieuYA0nGjywEukhK1dKBfRdby_4yY3E9SXA%40mail.gmail.com
This commit is contained in:
Robert Haas
2023-10-02 11:40:07 -04:00
parent e64c733bb1
commit 1ccc1e05ae
3 changed files with 55 additions and 49 deletions
Download Patch File Download Diff File Expand all files Collapse all files

36
src/backend/access/heap/pruneheap.c
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@ -53,16 +53,6 @@ typedef struct
* 1. Otherwise every access would need to subtract 1.
*/
bool marked[MaxHeapTuplesPerPage + 1];
/*
* Tuple visibility is only computed once for each tuple, for correctness
* and efficiency reasons; see comment in heap_page_prune() for details.
* This is of type int8[], instead of HTSV_Result[], so we can use -1 to
* indicate no visibility has been computed, e.g. for LP_DEAD items.
*
* Same indexing as ->marked.
*/
int8 htsv[MaxHeapTuplesPerPage + 1];
} PruneState;
/* Local functions */
@ -71,6 +61,7 @@ static HTSV_Result heap_prune_satisfies_vacuum(PruneState *prstate,
Buffer buffer);
static int heap_prune_chain(Buffer buffer,
OffsetNumber rootoffnum,
int8 *htsv,
PruneState *prstate);
static void heap_prune_record_prunable(PruneState *prstate, TransactionId xid);
static void heap_prune_record_redirect(PruneState *prstate,
@ -240,6 +231,10 @@ heap_page_prune(Relation relation, Buffer buffer,
prstate.nredirected = prstate.ndead = prstate.nunused = 0;
memset(prstate.marked, 0, sizeof(prstate.marked));
/*
* presult->htsv is not initialized here because all ntuple spots in the
* array will be set either to a valid HTSV_Result value or -1.
*/
presult->ndeleted = 0;
presult->nnewlpdead = 0;
@ -276,7 +271,7 @@ heap_page_prune(Relation relation, Buffer buffer,
/* Nothing to do if slot doesn't contain a tuple */
if (!ItemIdIsNormal(itemid))
{
prstate.htsv[offnum] = -1;
presult->htsv[offnum] = -1;
continue;
}
@ -292,8 +287,8 @@ heap_page_prune(Relation relation, Buffer buffer,
if (off_loc)
*off_loc = offnum;
prstate.htsv[offnum] = heap_prune_satisfies_vacuum(&prstate, &tup,
buffer);
presult->htsv[offnum] = heap_prune_satisfies_vacuum(&prstate, &tup,
buffer);
}
/* Scan the page */
@ -317,7 +312,8 @@ heap_page_prune(Relation relation, Buffer buffer,
continue;
/* Process this item or chain of items */
presult->ndeleted += heap_prune_chain(buffer, offnum, &prstate);
presult->ndeleted += heap_prune_chain(buffer, offnum,
presult->htsv, &prstate);
}
/* Clear the offset information once we have processed the given page. */
@ -446,6 +442,8 @@ heap_prune_satisfies_vacuum(PruneState *prstate, HeapTuple tup, Buffer buffer)
/*
* Prune specified line pointer or a HOT chain originating at line pointer.
*
* Tuple visibility information is provided in htsv.
*
* If the item is an index-referenced tuple (i.e. not a heap-only tuple),
* the HOT chain is pruned by removing all DEAD tuples at the start of the HOT
* chain. We also prune any RECENTLY_DEAD tuples preceding a DEAD tuple.
@ -473,7 +471,8 @@ 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, PruneState *prstate)
heap_prune_chain(Buffer buffer, OffsetNumber rootoffnum,
int8 *htsv, PruneState *prstate)
{
int ndeleted = 0;
Page dp = (Page) BufferGetPage(buffer);
@ -494,7 +493,7 @@ heap_prune_chain(Buffer buffer, OffsetNumber rootoffnum, PruneState *prstate)
*/
if (ItemIdIsNormal(rootlp))
{
Assert(prstate->htsv[rootoffnum] != -1);
Assert(htsv[rootoffnum] != -1);
htup = (HeapTupleHeader) PageGetItem(dp, rootlp);
if (HeapTupleHeaderIsHeapOnly(htup))
@ -517,7 +516,7 @@ heap_prune_chain(Buffer buffer, OffsetNumber rootoffnum, PruneState *prstate)
* either here or while following a chain below. Whichever path
* gets there first will mark the tuple unused.
*/
if (prstate->htsv[rootoffnum] == HEAPTUPLE_DEAD &&
if (htsv[rootoffnum] == HEAPTUPLE_DEAD &&
!HeapTupleHeaderIsHotUpdated(htup))
{
heap_prune_record_unused(prstate, rootoffnum);
@ -585,7 +584,6 @@ heap_prune_chain(Buffer buffer, OffsetNumber rootoffnum, PruneState *prstate)
break;
Assert(ItemIdIsNormal(lp));
Assert(prstate->htsv[offnum] != -1);
htup = (HeapTupleHeader) PageGetItem(dp, lp);
/*
@ -605,7 +603,7 @@ heap_prune_chain(Buffer buffer, OffsetNumber rootoffnum, PruneState *prstate)
*/
tupdead = recent_dead = false;
switch ((HTSV_Result) prstate->htsv[offnum])
switch (htsv_get_valid_status(htsv[offnum]))
{
case HEAPTUPLE_DEAD:
tupdead = true;