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Adjust btbulkdelete logic so that only one WAL record is issued while 

deleting multiple index entries on a single index page.  This makes for
a very substantial reduction in the amount of WAL traffic during a
large delete operation.
This commit is contained in:
Tom Lane 2003-02-23 22:43:09 +00:00
parent 13dadef8b5
commit 3bbd6af37c
4 changed files with 135 additions and 107 deletions
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45
src/backend/access/nbtree/nbtpage.c
View File

@ -9,7 +9,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/access/nbtree/nbtpage.c,v 1.61 2003/02/23 06:17:13 tgl Exp $
* $Header: /cvsroot/pgsql/src/backend/access/nbtree/nbtpage.c,v 1.62 2003/02/23 22:43:08 tgl Exp $
*
* NOTES
* Postgres btree pages look like ordinary relation pages. The opaque
@ -618,26 +618,34 @@ _bt_metaproot(Relation rel, BlockNumber rootbknum, uint32 level)
}
/*
* Delete an item from a btree page.
* Delete item(s) from a btree page.
*
* This must only be used for deleting leaf items. Deleting an item on a
* non-leaf page has to be done as part of an atomic action that includes
* deleting the page it points to.
*
* This routine assumes that the caller has pinned and locked the buffer,
* and will write the buffer afterwards.
* and will write the buffer afterwards. Also, the given itemnos *must*
* appear in increasing order in the array.
*/
void
_bt_itemdel(Relation rel, Buffer buf, ItemPointer tid)
_bt_delitems(Relation rel, Buffer buf,
OffsetNumber *itemnos, int nitems)
{
Page page = BufferGetPage(buf);
OffsetNumber offno;
offno = ItemPointerGetOffsetNumber(tid);
int i;
/* No elog(ERROR) until changes are logged */
START_CRIT_SECTION();
PageIndexTupleDelete(page, offno);
/*
* Delete the items in reverse order so we don't have to think about
* adjusting item numbers for previous deletions.
*/
for (i = nitems - 1; i >= 0; i--)
{
PageIndexTupleDelete(page, itemnos[i]);
}
/* XLOG stuff */
if (!rel->rd_istemp)
@ -646,17 +654,30 @@ _bt_itemdel(Relation rel, Buffer buf, ItemPointer tid)
XLogRecPtr recptr;
XLogRecData rdata[2];
xlrec.target.node = rel->rd_node;
xlrec.target.tid = *tid;
xlrec.node = rel->rd_node;
xlrec.block = BufferGetBlockNumber(buf);
rdata[0].buffer = InvalidBuffer;
rdata[0].data = (char *) &xlrec;
rdata[0].len = SizeOfBtreeDelete;
rdata[0].next = &(rdata[1]);
/*
* The target-offsets array is not in the buffer, but pretend
* that it is. When XLogInsert stores the whole buffer, the offsets
* array need not be stored too.
*/
rdata[1].buffer = buf;
rdata[1].data = NULL;
rdata[1].len = 0;
if (nitems > 0)
{
rdata[1].data = (char *) itemnos;
rdata[1].len = nitems * sizeof(OffsetNumber);
}
else
{
rdata[1].data = NULL;
rdata[1].len = 0;
}
rdata[1].next = NULL;
recptr = XLogInsert(RM_BTREE_ID, XLOG_BTREE_DELETE, rdata);

155
src/backend/access/nbtree/nbtree.c
View File

@ -12,7 +12,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/access/nbtree/nbtree.c,v 1.97 2003/02/23 06:17:13 tgl Exp $
* $Header: /cvsroot/pgsql/src/backend/access/nbtree/nbtree.c,v 1.98 2003/02/23 22:43:08 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -572,121 +572,110 @@ btbulkdelete(PG_FUNCTION_ARGS)
IndexBulkDeleteCallback callback = (IndexBulkDeleteCallback) PG_GETARG_POINTER(1);
void *callback_state = (void *) PG_GETARG_POINTER(2);
IndexBulkDeleteResult *result;
BlockNumber num_pages;
double tuples_removed;
double num_index_tuples;
IndexScanDesc scan;
BTScanOpaque so;
ItemPointer current;
OffsetNumber deletable[BLCKSZ / sizeof(OffsetNumber)];
int ndeletable;
Buffer buf;
BlockNumber num_pages;
tuples_removed = 0;
num_index_tuples = 0;
/*
* We use a standard IndexScanDesc scan object, but to speed up the
* loop, we skip most of the wrapper layers of index_getnext and
* instead call _bt_step directly. This implies holding buffer lock
* on a target page throughout the loop over the page's tuples.
* The outer loop iterates over index leaf pages, the inner over items
* on a leaf page. We issue just one _bt_delitems() call per page,
* so as to minimize WAL traffic.
*
* Whenever we step onto a new page, we have to trade in the read
* lock acquired by _bt_first or _bt_step for an exclusive write lock
* (fortunately, _bt_relbuf doesn't care which kind of lock it's
* releasing when it comes time for _bt_step to release our lock).
*
* Note that we exclusive-lock every leaf page, or at least every one
* containing data items. It sounds attractive to only exclusive-lock
* Note that we exclusive-lock every leaf page containing data items,
* in sequence left to right. It sounds attractive to only exclusive-lock
* those containing items we need to delete, but unfortunately that
* is not safe: we could then pass a stopped indexscan, which could
* in rare cases lead to deleting the item it needs to find when it
* resumes. (See _bt_restscan --- this could only happen if an indexscan
* stops on a deletable item and then a page split moves that item
* into a page further to its right, which the indexscan will have no
* pin on.)
* pin on.) We can skip obtaining exclusive lock on empty pages
* though, since no indexscan could be stopped on those.
*/
scan = index_beginscan(NULL, rel, SnapshotAny, 0, (ScanKey) NULL);
so = (BTScanOpaque) scan->opaque;
current = &(scan->currentItemData);
/* Use _bt_first to get started, then _bt_step to remaining tuples */
if (_bt_first(scan, ForwardScanDirection))
buf = _bt_get_endpoint(rel, 0, false);
if (BufferIsValid(buf)) /* check for empty index */
{
Buffer buf;
BlockNumber lockedBlock = InvalidBlockNumber;
/* we have the buffer pinned and read-locked */
buf = so->btso_curbuf;
Assert(BufferIsValid(buf));
do
for (;;)
{
Page page;
BlockNumber blkno;
OffsetNumber offnum;
BTItem btitem;
BTPageOpaque opaque;
IndexTuple itup;
ItemPointer htup;
OffsetNumber offnum,
minoff,
maxoff;
BlockNumber nextpage;
CHECK_FOR_INTERRUPTS();
/* current is the next index tuple */
ndeletable = 0;
page = BufferGetPage(buf);
blkno = ItemPointerGetBlockNumber(current);
/*
* Make sure we have a super-exclusive write lock on this page.
*
* We assume that only concurrent insertions, not deletions,
* can occur while we're not holding the page lock (the
* caller should hold a suitable relation lock to ensure
* this). Therefore, no items can escape being scanned because
* of this temporary lock release.
*/
if (blkno != lockedBlock)
opaque = (BTPageOpaque) PageGetSpecialPointer(page);
minoff = P_FIRSTDATAKEY(opaque);
maxoff = PageGetMaxOffsetNumber(page);
/* We probably cannot see deleted pages, but skip 'em if so */
if (minoff <= maxoff && !P_ISDELETED(opaque))
{
/*
* Trade in the initial read lock for a super-exclusive
* write lock on this page.
*/
LockBuffer(buf, BUFFER_LOCK_UNLOCK);
LockBufferForCleanup(buf);
lockedBlock = blkno;
/*
* If the page was formerly rightmost but was split while we
* didn't hold the lock, and ip_posid is pointing to item
* 1, then ip_posid now points at the high key not a valid
* data item. In this case we need to step forward.
* Recompute minoff/maxoff, both of which could have changed
* while we weren't holding the lock.
*/
opaque = (BTPageOpaque) PageGetSpecialPointer(page);
if (current->ip_posid < P_FIRSTDATAKEY(opaque))
current->ip_posid = P_FIRSTDATAKEY(opaque);
minoff = P_FIRSTDATAKEY(opaque);
maxoff = PageGetMaxOffsetNumber(page);
/*
* Scan over all items to see which ones need deleted
* according to the callback function.
*/
for (offnum = minoff;
offnum <= maxoff;
offnum = OffsetNumberNext(offnum))
{
BTItem btitem;
ItemPointer htup;
btitem = (BTItem) PageGetItem(page,
PageGetItemId(page, offnum));
htup = &(btitem->bti_itup.t_tid);
if (callback(htup, callback_state))
{
deletable[ndeletable++] = offnum;
tuples_removed += 1;
}
else
num_index_tuples += 1;
}
}
offnum = ItemPointerGetOffsetNumber(current);
btitem = (BTItem) PageGetItem(page, PageGetItemId(page, offnum));
itup = &btitem->bti_itup;
htup = &(itup->t_tid);
if (callback(htup, callback_state))
/*
* If we need to delete anything, do it and write the buffer;
* else just release the buffer.
*/
nextpage = opaque->btpo_next;
if (ndeletable > 0)
{
/* Okay to delete the item from the page */
_bt_itemdel(rel, buf, current);
/* Mark buffer dirty, but keep the lock and pin */
WriteNoReleaseBuffer(buf);
tuples_removed += 1;
/*
* We now need to back up the scan one item, so that the next
* cycle will re-examine the same offnum on this page (which
* now holds the next item).
*/
current->ip_posid--;
_bt_delitems(rel, buf, deletable, ndeletable);
_bt_wrtbuf(rel, buf);
}
else
num_index_tuples += 1;
} while (_bt_step(scan, &buf, ForwardScanDirection));
{
_bt_relbuf(rel, buf);
}
/* And advance to next page, if any */
if (nextpage == P_NONE)
break;
buf = _bt_getbuf(rel, nextpage, BT_READ);
}
}
index_endscan(scan);
/* return statistics */
num_pages = RelationGetNumberOfBlocks(rel);
@ -765,7 +754,7 @@ btvacuumcleanup(PG_FUNCTION_ARGS)
}
}
else if ((opaque->btpo_flags & BTP_HALF_DEAD) ||
P_FIRSTDATAKEY(opaque) > PageGetMaxOffsetNumber(page))
P_FIRSTDATAKEY(opaque) > PageGetMaxOffsetNumber(page))
{
/* Empty, try to delete */
int ndel;

27
src/backend/access/nbtree/nbtxlog.c
View File

@ -8,7 +8,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/access/nbtree/nbtxlog.c,v 1.2 2003/02/23 06:17:13 tgl Exp $
* $Header: /cvsroot/pgsql/src/backend/access/nbtree/nbtxlog.c,v 1.3 2003/02/23 22:43:08 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -379,11 +379,10 @@ btree_xlog_delete(bool redo, XLogRecPtr lsn, XLogRecord *record)
return;
xlrec = (xl_btree_delete *) XLogRecGetData(record);
reln = XLogOpenRelation(redo, RM_BTREE_ID, xlrec->target.node);
reln = XLogOpenRelation(redo, RM_BTREE_ID, xlrec->node);
if (!RelationIsValid(reln))
return;
buffer = XLogReadBuffer(false, reln,
ItemPointerGetBlockNumber(&(xlrec->target.tid)));
buffer = XLogReadBuffer(false, reln, xlrec->block);
if (!BufferIsValid(buffer))
elog(PANIC, "btree_delete_redo: block unfound");
page = (Page) BufferGetPage(buffer);
@ -396,7 +395,21 @@ btree_xlog_delete(bool redo, XLogRecPtr lsn, XLogRecord *record)
return;
}
PageIndexTupleDelete(page, ItemPointerGetOffsetNumber(&(xlrec->target.tid)));
if (record->xl_len > SizeOfBtreeDelete)
{
OffsetNumber *unused;
OffsetNumber *unend;
unused = (OffsetNumber *) ((char *) xlrec + SizeOfBtreeDelete);
unend = (OffsetNumber *) ((char *) xlrec + record->xl_len);
/* be careful to delete from back to front */
while (unused < unend)
{
unend--;
PageIndexTupleDelete(page, *unend);
}
}
PageSetLSN(page, lsn);
PageSetSUI(page, ThisStartUpID);
@ -853,8 +866,8 @@ btree_desc(char *buf, uint8 xl_info, char *rec)
{
xl_btree_delete *xlrec = (xl_btree_delete *) rec;
strcat(buf, "delete: ");
out_target(buf, &(xlrec->target));
sprintf(buf + strlen(buf), "delete: node %u/%u; blk %u",
xlrec->node.tblNode, xlrec->node.relNode, xlrec->block);
break;
}
case XLOG_BTREE_DELETE_PAGE:

15
src/include/access/nbtree.h
View File

@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $Id: nbtree.h,v 1.66 2003/02/23 06:17:13 tgl Exp $
* $Id: nbtree.h,v 1.67 2003/02/23 22:43:09 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -263,14 +263,18 @@ typedef struct xl_btree_split
#define SizeOfBtreeSplit (offsetof(xl_btree_split, leftlen) + sizeof(uint16))
/*
* This is what we need to know about delete of an individual leaf btitem
* This is what we need to know about delete of individual leaf btitems.
* The WAL record can represent deletion of any number of btitems on a
* single index page.
*/
typedef struct xl_btree_delete
{
xl_btreetid target; /* deleted tuple id */
RelFileNode node;
BlockNumber block;
/* TARGET OFFSET NUMBERS FOLLOW AT THE END */
} xl_btree_delete;
#define SizeOfBtreeDelete (offsetof(xl_btreetid, tid) + SizeOfIptrData)
#define SizeOfBtreeDelete (offsetof(xl_btree_delete, block) + sizeof(BlockNumber))
/*
* This is what we need to know about deletion of a btree page. The target
@ -453,7 +457,8 @@ extern void _bt_wrtnorelbuf(Relation rel, Buffer buf);
extern void _bt_pageinit(Page page, Size size);
extern bool _bt_page_recyclable(Page page);
extern void _bt_metaproot(Relation rel, BlockNumber rootbknum, uint32 level);
extern void _bt_itemdel(Relation rel, Buffer buf, ItemPointer tid);
extern void _bt_delitems(Relation rel, Buffer buf,
OffsetNumber *itemnos, int nitems);
extern int _bt_pagedel(Relation rel, Buffer buf, bool vacuum_full);
/*