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Add explanatory comment to prune_freeze_setup()

author Melanie Plageman <melanieplageman@gmail.com>

2025年12月16日 15:30:14 +0000 (10:30 -0500)

committer Melanie Plageman <melanieplageman@gmail.com>

2025年12月16日 16:04:07 +0000 (11:04 -0500)

heap_page_prune_and_freeze() fills in PruneState->deadoffsets, the array
of OffsetNumbers of dead tuples. It is returned to the caller in the
PruneFreezeResult. To avoid having two copies of the array, the
PruneState saves only a pointer to the array. This was a bit unusual and
confusing, so add a clarifying comment.

Author: Melanie Plageman <melanieplageman@gmail.com>
Suggested-by: Chao Li <li.evan.chao@gmail.com>
Discussion: https://postgr.es/m/CAEoWx2=jiD1nqch4JQN+odAxZSD7mRvdoHUGJYN2r6tQG_66yQ@mail.gmail.com

src/backend/access/heap/pruneheap.c patch | blob | blame | history

diff --git a/src/backend/access/heap/pruneheap.c b/src/backend/access/heap/pruneheap.c

index f99d92725b8841cb59549ceaabe6b0d310f3330a..07aa08cfe14d6ef4dd730fae1b2f4511d3a5f902 100644 (file)

--- a/src/backend/access/heap/pruneheap.c

+++ b/src/backend/access/heap/pruneheap.c

@@ -385,6 +385,13 @@ prune_freeze_setup(PruneFreezeParams *params,

prstate->recently_dead_tuples = 0;

prstate->hastup = false;

prstate->lpdead_items = 0;

+ /*

+ * deadoffsets are filled in during pruning but are only used to populate

+ * PruneFreezeResult->deadoffsets. To avoid needing two copies of the

+ * array, just save a pointer to the result offsets array in the

+ * PruneState.

+ */

prstate->deadoffsets = presult->deadoffsets;

prstate->frz_conflict_horizon = InvalidTransactionId;

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