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Update comment on VACUUM FULL.

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Manfred Koizar
This commit is contained in:
Bruce Momjian 2005-02-15 03:50:07 +00:00
parent b39ce1ccec
commit 3110cd237c
1 changed files with 13 additions and 8 deletions
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21
src/backend/commands/vacuum.c
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@ -13,7 +13,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.299 2004/12/31 21:59:42 pgsql Exp $
* $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.300 2005/02/15 03:50:07 momjian Exp $
*
*-------------------------------------------------------------------------
*/
@ -1703,20 +1703,25 @@ repair_frag(VRelStats *vacrelstats, Relation onerel,
tuple_len = tuple.t_len = ItemIdGetLength(itemid);
ItemPointerSet(&(tuple.t_self), blkno, offnum);
/*
/* ---
* VACUUM FULL has an exclusive lock on the relation. So
* normally no other transaction can have pending INSERTs or
* DELETEs in this relation. A tuple is either (a) a tuple in
* a system catalog, inserted or deleted by a not yet
* committed transaction or (b) dead (XMIN_INVALID or
* XMAX_COMMITTED) or (c) inserted by a committed xact
* (XMIN_COMMITTED) or (d) moved by the currently running
* VACUUM. In case (a) we wouldn't be in repair_frag() at all.
* DELETEs in this relation. A tuple is either:
* (a) a tuple in a system catalog, inserted or deleted
* by a not yet committed transaction
* (b) known dead (XMIN_INVALID, or XMAX_COMMITTED and xmax
* is visible to all active transactions)
* (c) inserted by a committed xact (XMIN_COMMITTED)
* (d) moved by the currently running VACUUM.
* (e) deleted (XMAX_COMMITTED) but at least one active
* transaction does not see the deleting transaction
* In case (a) we wouldn't be in repair_frag() at all.
* In case (b) we cannot be here, because scan_heap() has
* already marked the item as unused, see continue above. Case
* (c) is what normally is to be expected. Case (d) is only
* possible, if a whole tuple chain has been moved while
* processing this or a higher numbered block.
* ---
*/
if (!(tuple.t_data->t_infomask & HEAP_XMIN_COMMITTED))
{