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Modify btree to delete known-dead index entries without an actual VACUUM.

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When we are about to split an index page to do an insertion, first look
to see if any entries marked LP_DELETE exist on the page, and if so remove
them to try to make enough space for the desired insert.  This should reduce
index bloat in heavily-updated tables, although of course you still need
VACUUM eventually to clean up the heap.

Junji Teramoto
This commit is contained in:
Tom Lane
2006-07-25 19:13:00 +00:00
parent edd49fcf69
commit e6284649b9
6 changed files with 144 additions and 16 deletions
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81
src/backend/access/nbtree/nbtinsert.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/access/nbtree/nbtinsert.c,v 1.141 2006/07/13 16:49:12 momjian Exp $
* $PostgreSQL: pgsql/src/backend/access/nbtree/nbtinsert.c,v 1.142 2006/07/25 19:13:00 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -65,6 +65,7 @@ static void _bt_pgaddtup(Relation rel, Page page,
OffsetNumber itup_off, const char *where);
static bool _bt_isequal(TupleDesc itupdesc, Page page, OffsetNumber offnum,
int keysz, ScanKey scankey);
static void _bt_vacuum_one_page(Relation rel, Buffer buffer);
/*
@ -262,6 +263,8 @@ _bt_check_unique(Relation rel, IndexTuple itup, Relation heapRel,
hbuffer) == HEAPTUPLE_DEAD)
{
curitemid->lp_flags |= LP_DELETE;
opaque->btpo_flags |= BTP_HAS_GARBAGE;
/* be sure to mark the proper buffer dirty... */
if (nbuf != InvalidBuffer)
SetBufferCommitInfoNeedsSave(nbuf);
else
@ -424,11 +427,29 @@ _bt_insertonpg(Relation rel,
*/
bool movedright = false;
while (PageGetFreeSpace(page) < itemsz &&
!P_RIGHTMOST(lpageop) &&
_bt_compare(rel, keysz, scankey, page, P_HIKEY) == 0 &&
random() > (MAX_RANDOM_VALUE / 100))
while (PageGetFreeSpace(page) < itemsz)
{
Buffer rbuf;
/*
* before considering moving right, see if we can obtain enough
* space by erasing LP_DELETE items
*/
if (P_ISLEAF(lpageop) && P_HAS_GARBAGE(lpageop))
{
_bt_vacuum_one_page(rel, buf);
if (PageGetFreeSpace(page) >= itemsz)
break; /* OK, now we have enough space */
}
/*
* nope, so check conditions (b) and (c) enumerated above
*/
if (P_RIGHTMOST(lpageop) ||
_bt_compare(rel, keysz, scankey, page, P_HIKEY) != 0 ||
random() <= (MAX_RANDOM_VALUE / 100))
break;
/*
* step right to next non-dead page
*
@ -438,7 +459,7 @@ _bt_insertonpg(Relation rel,
* pages won't do because we don't know when they will get
* de-linked from the tree.
*/
Buffer rbuf = InvalidBuffer;
rbuf = InvalidBuffer;
for (;;)
{
@ -702,9 +723,9 @@ _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 */
/* also, clear the SPLIT_END and HAS_GARBAGE flags in both pages */
lopaque->btpo_flags = oopaque->btpo_flags;
lopaque->btpo_flags &= ~(BTP_ROOT | BTP_SPLIT_END);
lopaque->btpo_flags &= ~(BTP_ROOT | BTP_SPLIT_END | BTP_HAS_GARBAGE);
ropaque->btpo_flags = lopaque->btpo_flags;
lopaque->btpo_prev = oopaque->btpo_prev;
lopaque->btpo_next = BufferGetBlockNumber(rbuf);
@ -1651,3 +1672,47 @@ _bt_isequal(TupleDesc itupdesc, Page page, OffsetNumber offnum,
/* if we get here, the keys are equal */
return true;
}
/*
* _bt_vacuum_one_page - vacuum just one index page.
*
* Try to remove LP_DELETE items from the given page. The passed buffer
* must be exclusive-locked, but unlike a real VACUUM, we don't need a
* super-exclusive "cleanup" lock (see nbtree/README).
*/
static void
_bt_vacuum_one_page(Relation rel, Buffer buffer)
{
OffsetNumber deletable[MaxOffsetNumber];
int ndeletable = 0;
OffsetNumber offnum,
minoff,
maxoff;
Page page = BufferGetPage(buffer);
BTPageOpaque opaque = (BTPageOpaque) PageGetSpecialPointer(page);
/*
* Scan over all items to see which ones need deleted
* according to LP_DELETE flags.
*/
minoff = P_FIRSTDATAKEY(opaque);
maxoff = PageGetMaxOffsetNumber(page);
for (offnum = minoff;
offnum <= maxoff;
offnum = OffsetNumberNext(offnum))
{
ItemId itemId = PageGetItemId(page, offnum);
if (ItemIdDeleted(itemId))
deletable[ndeletable++] = offnum;
}
if (ndeletable > 0)
_bt_delitems(rel, buffer, deletable, ndeletable);
/*
* Note: if we didn't find any LP_DELETE items, then the page's
* BTP_HAS_GARBAGE hint bit is falsely set. We do not bother
* expending a separate write to clear it, however. We will clear
* it when we split the page.
*/
}