Add explanatory comment to prune_freeze_setup()

melanieplageman · melanieplageman · commit bfe5c4bec750 · 2025-12-16T11:04:07.000-05:00
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
diff --git 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;
 
