From f9be3079cf0ff26b8ef603a9b0c8bc5d27561499 Mon Sep 17 00:00:00 2001 From: Matthias van de Meent Date: Tue, 9 Mar 2021 14:42:52 +0100 Subject: [PATCH v1] Truncate a pages' line pointer array when it has trailing unused ItemIds. This will allow reuse of what is effectively free space for data as well as new line pointers, instead of keeping it reserved for line pointers only. An additional benefit is that the HasFreeLinePointers hint-bit optimization now doesn't hint for free line pointers at the end of the array, slightly increasing the specificity of where the free lines are; and saving us from needing to search to the end of the array if all other entries are already filled. --- src/backend/storage/page/bufpage.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/src/backend/storage/page/bufpage.c b/src/backend/storage/page/bufpage.c index 9ac556b4ae..10d8f26ad0 100644 --- a/src/backend/storage/page/bufpage.c +++ b/src/backend/storage/page/bufpage.c @@ -672,7 +672,11 @@ compactify_tuples(itemIdCompact itemidbase, int nitems, Page page, bool presorte * PageRepairFragmentation * * Frees fragmented space on a page. - * It doesn't remove unused line pointers! Please don't change this. + * It doesn't remove intermediate unused line pointers (that would mean + * moving ItemIds, and that would imply invalidating indexed values), but it + * does truncate the page->pd_linp array to the last unused line pointer, so + * that this space may also be reused for data, instead of only for line + * pointers. * * This routine is usable for heap pages only, but see PageIndexMultiDelete. * @@ -691,6 +695,7 @@ PageRepairFragmentation(Page page) int nline, nstorage, nunused; + OffsetNumber lastUsed = InvalidOffsetNumber; int i; Size totallen; bool presorted = true; /* For now */ @@ -724,6 +729,7 @@ PageRepairFragmentation(Page page) lp = PageGetItemId(page, i); if (ItemIdIsUsed(lp)) { + lastUsed = i; if (ItemIdHasStorage(lp)) { itemidptr->offsetindex = i - 1; @@ -771,6 +777,11 @@ PageRepairFragmentation(Page page) compactify_tuples(itemidbase, nstorage, page, presorted); } + if (lastUsed != nline) { + ((PageHeader) page)->pd_lower = SizeOfPageHeaderData + (sizeof(ItemIdData) * lastUsed); + nunused = nunused - (nline - lastUsed); + } + /* Set hint bit for PageAddItem */ if (nunused > 0) PageSetHasFreeLinePointers(page); -- 2.20.1