From cecde97577fafddc6b3aa354b9b77a3a54b063a9 Mon Sep 17 00:00:00 2001 From: Bruce Momjian Date: Sun, 19 Sep 2010 17:51:44 +0000 Subject: [PATCH] Update HOT README about when single-page vacuums happen. --- src/backend/access/heap/README.HOT | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/src/backend/access/heap/README.HOT b/src/backend/access/heap/README.HOT index 2f9162e52d..d32b7f59ab 100644 --- a/src/backend/access/heap/README.HOT +++ b/src/backend/access/heap/README.HOT @@ -1,4 +1,4 @@ -$PostgreSQL: pgsql/src/backend/access/heap/README.HOT,v 1.6 2010/04/23 23:21:44 rhaas Exp $ +$PostgreSQL: pgsql/src/backend/access/heap/README.HOT,v 1.7 2010/09/19 17:51:44 momjian Exp $ Heap Only Tuples (HOT) ====================== @@ -246,6 +246,12 @@ scans reasonably sized, the maximum number of line pointers per page is arbitrarily capped at MaxHeapTuplesPerPage (the most tuples that could fit without HOT pruning). +Effectively, space reclamation happens during tuple retrieval when the +page is nearly full (<10% free) and a buffer cleanup lock can be +acquired. This means that UPDATE, DELETE, and SELECT can trigger space +reclamation, but often not during INSERT ... VALUES because it does +not retrieve a row. + VACUUM ------