From fc0c342f4946149914854eea8b5b7f88405d87f8 Mon Sep 17 00:00:00 2001 From: Tomas Vondra Date: Fri, 30 Oct 2026 16:01:29 +0100 Subject: [PATCH vmaster 2/4] Fix BRIN minmax-multi distance for tid values The distance function for tid values maps item pointers to float8 as (block * MaxHeapTuplesPerPage + offset) but the multiplication was done in uint32 arithmetic, so for high block values (above 14759338, ~112GB) the result wrapped around. The distance would then be very inaccurate (possibly negative), resulting in a less efficient index. Fix by doing the arithmetics in double. It's also possible the (user-supplied) item pointers have offsets greater than MaxHeapTuplesPerPage, confusing the mapping to double value. This commit does not try to address that, it's not clear what would be a better mapping. Author: Tomas Vondra Backpatch-through: 14 Discussion: https://postgr.es/m/CALdSSPgBvXz-VSF0p-5k%3D_uFfN38cWrERmm_AC4K67N6MWQhmg%40mail.gmail.com --- src/backend/access/brin/brin_minmax_multi.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/src/backend/access/brin/brin_minmax_multi.c b/src/backend/access/brin/brin_minmax_multi.c index 8bb5bd1b1e4..08e68cb48f4 100644 --- a/src/backend/access/brin/brin_minmax_multi.c +++ b/src/backend/access/brin/brin_minmax_multi.c @@ -2005,10 +2005,10 @@ brin_minmax_multi_distance_tid(PG_FUNCTION_ARGS) * We use the no-check variants here, because user-supplied values may * have (ip_posid == 0). See ItemPointerCompare. */ - da1 = ItemPointerGetBlockNumberNoCheck(pa1) * MaxHeapTuplesPerPage + + da1 = (double) ItemPointerGetBlockNumberNoCheck(pa1) * MaxHeapTuplesPerPage + ItemPointerGetOffsetNumberNoCheck(pa1); - da2 = ItemPointerGetBlockNumberNoCheck(pa2) * MaxHeapTuplesPerPage + + da2 = (double) ItemPointerGetBlockNumberNoCheck(pa2) * MaxHeapTuplesPerPage + ItemPointerGetOffsetNumberNoCheck(pa2); PG_RETURN_FLOAT8(da2 - da1); -- 2.55.0