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Update HOT README about when single-page vacuums happen.

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This commit is contained in:
Bruce Momjian 2010-09-19 17:51:44 +00:00
parent f679cfe97b
commit cecde97577
1 changed files with 7 additions and 1 deletions
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8
src/backend/access/heap/README.HOT
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@ -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
------