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HOT updates. When we update a tuple without changing any of its indexed

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columns, and the new version can be stored on the same heap page, we no longer
generate extra index entries for the new version.  Instead, index searches
follow the HOT-chain links to ensure they find the correct tuple version.

In addition, this patch introduces the ability to "prune" dead tuples on a
per-page basis, without having to do a complete VACUUM pass to recover space.
VACUUM is still needed to clean up dead index entries, however.

Pavan Deolasee, with help from a bunch of other people.
This commit is contained in:
Tom Lane
2007-09-20 17:56:33 +00:00
parent bbf4fdc253
commit 282d2a03dd
65 changed files with 3517 additions and 514 deletions
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81
src/backend/access/nbtree/nbtinsert.c
View File

@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/access/nbtree/nbtinsert.c,v 1.159 2007/09/12 22:10:26 tgl Exp $
* $PostgreSQL: pgsql/src/backend/access/nbtree/nbtinsert.c,v 1.160 2007/09/20 17:56:30 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -193,8 +193,6 @@ _bt_check_unique(Relation rel, IndexTuple itup, Relation heapRel,
*/
for (;;)
{
HeapTupleData htup;
Buffer hbuffer;
ItemId curitemid;
IndexTuple curitup;
BlockNumber nblkno;
@ -223,6 +221,9 @@ _bt_check_unique(Relation rel, IndexTuple itup, Relation heapRel,
*/
if (!ItemIdIsDead(curitemid))
{
ItemPointerData htid;
bool all_dead;
/*
* _bt_compare returns 0 for (1,NULL) and (1,NULL) - this's
* how we handling NULLs - and so we must not use _bt_compare
@ -234,17 +235,20 @@ _bt_check_unique(Relation rel, IndexTuple itup, Relation heapRel,
/* okay, we gotta fetch the heap tuple ... */
curitup = (IndexTuple) PageGetItem(page, curitemid);
htup.t_self = curitup->t_tid;
if (heap_fetch(heapRel, &SnapshotDirty, &htup, &hbuffer,
true, NULL))
htid = curitup->t_tid;
/*
* We check the whole HOT-chain to see if there is any tuple
* that satisfies SnapshotDirty. This is necessary because
* we have just a single index entry for the entire chain.
*/
if (heap_hot_search(&htid, heapRel, &SnapshotDirty, &all_dead))
{
/* it is a duplicate */
TransactionId xwait =
(TransactionIdIsValid(SnapshotDirty.xmin)) ?
SnapshotDirty.xmin : SnapshotDirty.xmax;
ReleaseBuffer(hbuffer);
/*
* If this tuple is being updated by other transaction
* then we have to wait for its commit/abort.
@ -263,15 +267,22 @@ _bt_check_unique(Relation rel, IndexTuple itup, Relation heapRel,
* is itself now committed dead --- if so, don't complain.
* This is a waste of time in normal scenarios but we must
* do it to support CREATE INDEX CONCURRENTLY.
*
* We must follow HOT-chains here because during
* concurrent index build, we insert the root TID though
* the actual tuple may be somewhere in the HOT-chain.
* While following the chain we might not stop at the exact
* tuple which triggered the insert, but that's OK because
* if we find a live tuple anywhere in this chain, we have
* a unique key conflict. The other live tuple is not part
* of this chain because it had a different index entry.
*/
htup.t_self = itup->t_tid;
if (heap_fetch(heapRel, SnapshotSelf, &htup, &hbuffer,
false, NULL))
htid = itup->t_tid;
if (heap_hot_search(&htid, heapRel, SnapshotSelf, NULL))
{
/* Normal case --- it's still live */
ReleaseBuffer(hbuffer);
}
else if (htup.t_data != NULL)
else
{
/*
* It's been deleted, so no error, and no need to
@ -279,39 +290,27 @@ _bt_check_unique(Relation rel, IndexTuple itup, Relation heapRel,
*/
break;
}
else
{
/* couldn't find the tuple?? */
elog(ERROR, "failed to fetch tuple being inserted");
}
ereport(ERROR,
(errcode(ERRCODE_UNIQUE_VIOLATION),
errmsg("duplicate key value violates unique constraint \"%s\"",
RelationGetRelationName(rel))));
}
else if (htup.t_data != NULL)
else if (all_dead)
{
/*
* Hmm, if we can't see the tuple, maybe it can be marked
* killed. This logic should match index_getnext and
* btgettuple.
* The conflicting tuple (or whole HOT chain) is dead to
* everyone, so we may as well mark the index entry
* killed.
*/
LockBuffer(hbuffer, BUFFER_LOCK_SHARE);
if (HeapTupleSatisfiesVacuum(htup.t_data, RecentGlobalXmin,
hbuffer) == HEAPTUPLE_DEAD)
{
ItemIdMarkDead(curitemid);
opaque->btpo_flags |= BTP_HAS_GARBAGE;
/* be sure to mark the proper buffer dirty... */
if (nbuf != InvalidBuffer)
SetBufferCommitInfoNeedsSave(nbuf);
else
SetBufferCommitInfoNeedsSave(buf);
}
LockBuffer(hbuffer, BUFFER_LOCK_UNLOCK);
ItemIdMarkDead(curitemid);
opaque->btpo_flags |= BTP_HAS_GARBAGE;
/* be sure to mark the proper buffer dirty... */
if (nbuf != InvalidBuffer)
SetBufferCommitInfoNeedsSave(nbuf);
else
SetBufferCommitInfoNeedsSave(buf);
}
ReleaseBuffer(hbuffer);
}
}
@ -840,7 +839,7 @@ _bt_split(Relation rel, Buffer buf, OffsetNumber firstright,
itemsz = ItemIdGetLength(itemid);
item = (IndexTuple) PageGetItem(origpage, itemid);
if (PageAddItem(rightpage, (Item) item, itemsz, rightoff,
false) == InvalidOffsetNumber)
false, false) == InvalidOffsetNumber)
elog(PANIC, "failed to add hikey to the right sibling");
rightoff = OffsetNumberNext(rightoff);
}
@ -865,7 +864,7 @@ _bt_split(Relation rel, Buffer buf, OffsetNumber firstright,
item = (IndexTuple) PageGetItem(origpage, itemid);
}
if (PageAddItem(leftpage, (Item) item, itemsz, leftoff,
false) == InvalidOffsetNumber)
false, false) == InvalidOffsetNumber)
elog(PANIC, "failed to add hikey to the left sibling");
leftoff = OffsetNumberNext(leftoff);
@ -1700,7 +1699,7 @@ _bt_newroot(Relation rel, Buffer lbuf, Buffer rbuf)
* benefit of _bt_restore_page().
*/
if (PageAddItem(rootpage, (Item) new_item, itemsz, P_HIKEY,
false) == InvalidOffsetNumber)
false, false) == InvalidOffsetNumber)
elog(PANIC, "failed to add leftkey to new root page");
pfree(new_item);
@ -1718,7 +1717,7 @@ _bt_newroot(Relation rel, Buffer lbuf, Buffer rbuf)
* insert the right page pointer into the new root page.
*/
if (PageAddItem(rootpage, (Item) new_item, itemsz, P_FIRSTKEY,
false) == InvalidOffsetNumber)
false, false) == InvalidOffsetNumber)
elog(PANIC, "failed to add rightkey to new root page");
pfree(new_item);
@ -1805,7 +1804,7 @@ _bt_pgaddtup(Relation rel,
}
if (PageAddItem(page, (Item) itup, itemsize, itup_off,
false) == InvalidOffsetNumber)
false, false) == InvalidOffsetNumber)
elog(PANIC, "failed to add item to the %s for \"%s\"",
where, RelationGetRelationName(rel));
}