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Accept slightly-filled pages for tuples larger than fillfactor.

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We always inserted a larger-than-fillfactor tuple into a newly-extended
page, even when existing pages were empty or contained nothing but an
unused line pointer.  This was unnecessary relation extension.  Start
tolerating page usage up to 1/8 the maximum space that could be taken up
by line pointers.  This is somewhat arbitrary, but it should allow more
cases to reuse pages.  This has no effect on tables with fillfactor=100
(the default).

John Naylor and Floris van Nee.  Reviewed by Matthias van de Meent.
Reported by Floris van Nee.

Discussion: https://postgr.es/m/6e263217180649339720afe2176c50aa@opammb0562.comp.optiver.com
This commit is contained in:
Noah Misch
2021-03-30 18:53:44 -07:00
parent 7ef64e7e72
commit 0ff8bbdee1
4 changed files with 74 additions and 18 deletions
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6
src/backend/access/heap/rewriteheap.c
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@@ -676,7 +676,11 @@ raw_heap_insert(RewriteState state, HeapTuple tup)
if (len + saveFreeSpace > pageFreeSpace)
{
/* Doesn't fit, so write out the existing page */
/*
* Doesn't fit, so write out the existing page. It always
* contains a tuple. Hence, unlike RelationGetBufferForTuple(),
* enforce saveFreeSpace unconditionally.
*/
/* XLOG stuff */
if (RelationNeedsWAL(state->rs_new_rel))