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Rewrite btree vacuuming to fold the former bulkdelete and cleanup operations

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into a single mostly-physical-order scan of the index.  This requires some
ticklish interlocking considerations, but should create no material
performance impact on normal index operations (at least given the
already-committed changes to make scans work a page at a time).  VACUUM
itself should get significantly faster in any index that's degenerated to a
very nonlinear page order.  Also, we save one pass over the index entirely,
except in the case where there were no deletions to do and so only one pass
happened anyway.

Original patch by Heikki Linnakangas, rework by Tom Lane.
This commit is contained in:
Tom Lane
2006-05-08 00:00:17 +00:00
parent 09cb5c0e7d
commit 5749f6ef0c
10 changed files with 692 additions and 253 deletions
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24
src/backend/access/nbtree/nbtinsert.c
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@@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/access/nbtree/nbtinsert.c,v 1.136 2006/04/25 22:46:05 tgl Exp $
* $PostgreSQL: pgsql/src/backend/access/nbtree/nbtinsert.c,v 1.137 2006/05/08 00:00:09 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -700,14 +700,18 @@ _bt_split(Relation rel, Buffer buf, OffsetNumber firstright,
ropaque = (BTPageOpaque) PageGetSpecialPointer(rightpage);
/* if we're splitting this page, it won't be the root when we're done */
/* also, clear the SPLIT_END flag in both pages */
lopaque->btpo_flags = oopaque->btpo_flags;
lopaque->btpo_flags &= ~BTP_ROOT;
lopaque->btpo_flags &= ~(BTP_ROOT | BTP_SPLIT_END);
ropaque->btpo_flags = lopaque->btpo_flags;
lopaque->btpo_prev = oopaque->btpo_prev;
lopaque->btpo_next = BufferGetBlockNumber(rbuf);
ropaque->btpo_prev = BufferGetBlockNumber(buf);
ropaque->btpo_next = oopaque->btpo_next;
lopaque->btpo.level = ropaque->btpo.level = oopaque->btpo.level;
/* Since we already have write-lock on both pages, ok to read cycleid */
lopaque->btpo_cycleid = _bt_vacuum_cycleid(rel);
ropaque->btpo_cycleid = lopaque->btpo_cycleid;
/*
* If the page we're splitting is not the rightmost page at its level in
@@ -836,6 +840,21 @@ _bt_split(Relation rel, Buffer buf, OffsetNumber firstright,
sopaque = (BTPageOpaque) PageGetSpecialPointer(spage);
if (sopaque->btpo_prev != ropaque->btpo_prev)
elog(PANIC, "right sibling's left-link doesn't match");
/*
* Check to see if we can set the SPLIT_END flag in the right-hand
* split page; this can save some I/O for vacuum since it need not
* proceed to the right sibling. We can set the flag if the right
* sibling has a different cycleid: that means it could not be part
* of a group of pages that were all split off from the same ancestor
* page. If you're confused, imagine that page A splits to A B and
* then again, yielding A C B, while vacuum is in progress. Tuples
* originally in A could now be in either B or C, hence vacuum must
* examine both pages. But if D, our right sibling, has a different
* cycleid then it could not contain any tuples that were in A when
* the vacuum started.
*/
if (sopaque->btpo_cycleid != ropaque->btpo_cycleid)
ropaque->btpo_flags |= BTP_SPLIT_END;
}
/*
@@ -1445,6 +1464,7 @@ _bt_newroot(Relation rel, Buffer lbuf, Buffer rbuf)
rootopaque->btpo_flags = BTP_ROOT;
rootopaque->btpo.level =
((BTPageOpaque) PageGetSpecialPointer(lpage))->btpo.level + 1;
rootopaque->btpo_cycleid = 0;
/* update metapage data */
metad->btm_root = rootblknum;