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Reduce WAL activity for page splits:

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> Currently, an index split writes all the data on the split page to
> WAL. That's a lot of WAL traffic. The tuples that are copied to the
> right page need to be WAL logged, but the tuples that stay on the
> original page don't.

Heikki Linnakangas
This commit is contained in:
Bruce Momjian
2007-02-08 05:05:53 +00:00
parent fe03a5f4ae
commit b79575ce45
3 changed files with 285 additions and 189 deletions
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144
src/backend/access/nbtree/nbtinsert.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/access/nbtree/nbtinsert.c,v 1.149 2007/02/06 14:55:11 tgl Exp $
* $PostgreSQL: pgsql/src/backend/access/nbtree/nbtinsert.c,v 1.150 2007/02/08 05:05:53 momjian Exp $
*
*-------------------------------------------------------------------------
*/
@ -733,6 +733,7 @@ _bt_split(Relation rel, Buffer buf, OffsetNumber firstright,
rightoff;
OffsetNumber maxoff;
OffsetNumber i;
bool isroot;
rbuf = _bt_getbuf(rel, P_NEW, BT_WRITE);
origpage = BufferGetPage(buf);
@ -747,6 +748,8 @@ _bt_split(Relation rel, Buffer buf, OffsetNumber firstright,
lopaque = (BTPageOpaque) PageGetSpecialPointer(leftpage);
ropaque = (BTPageOpaque) PageGetSpecialPointer(rightpage);
isroot = P_ISROOT(oopaque);
/* if we're splitting this page, it won't be the root when we're done */
/* also, clear the SPLIT_END and HAS_GARBAGE flags in both pages */
lopaque->btpo_flags = oopaque->btpo_flags;
@ -921,61 +924,116 @@ _bt_split(Relation rel, Buffer buf, OffsetNumber firstright,
MarkBufferDirty(sbuf);
}
/*
* By here, the original data page has been split into two new halves, and
* these are correct. The algorithm requires that the left page never
* move during a split, so we copy the new left page back on top of the
* original. Note that this is not a waste of time, since we also require
* (in the page management code) that the center of a page always be
* clean, and the most efficient way to guarantee this is just to compact
* the data by reinserting it into a new left page. (XXX the latter
* comment is probably obsolete.)
*
* We need to do this before writing the WAL record, so that XLogInsert can
* WAL log an image of the page if necessary.
*/
PageRestoreTempPage(leftpage, origpage);
/* XLOG stuff */
if (!rel->rd_istemp)
{
xl_btree_split xlrec;
uint8 xlinfo;
XLogRecPtr recptr;
XLogRecData rdata[4];
XLogRecData rdata[6];
XLogRecData *lastrdata;
xlrec.target.node = rel->rd_node;
ItemPointerSet(&(xlrec.target.tid), itup_blkno, itup_off);
if (newitemonleft)
xlrec.otherblk = BufferGetBlockNumber(rbuf);
else
xlrec.otherblk = BufferGetBlockNumber(buf);
xlrec.leftblk = lopaque->btpo_prev;
xlrec.rightblk = ropaque->btpo_next;
xlrec.node = rel->rd_node;
xlrec.leftsib = BufferGetBlockNumber(buf);
xlrec.rightsib = BufferGetBlockNumber(rbuf);
xlrec.firstright = firstright;
xlrec.rnext = ropaque->btpo_next;
xlrec.level = lopaque->btpo.level;
/*
rdata[0].data = (char *) &xlrec;
rdata[0].len = SizeOfBtreeSplit;
rdata[0].buffer = InvalidBuffer;
lastrdata = &rdata[0];
/* Log downlink on non-leaf pages. */
if (lopaque->btpo.level > 0)
{
lastrdata->next = lastrdata + 1;
lastrdata++;
lastrdata->data = (char *) &newitem->t_tid.ip_blkid;
lastrdata->len = sizeof(BlockIdData);
lastrdata->buffer = InvalidBuffer;
}
/* Log the new item, if it was inserted on the left page. If it was
* put on the right page, we don't need to explicitly WAL log it
* because it's included with all the other items on the right page.
*/
lastrdata->next = lastrdata + 1;
lastrdata++;
if (newitemonleft)
{
lastrdata->data = (char *) &newitemoff;
lastrdata->len = sizeof(OffsetNumber);
lastrdata->buffer = buf; /* backup block 1 */
lastrdata->buffer_std = true;
lastrdata->next = lastrdata + 1;
lastrdata++;
lastrdata->data = (char *)newitem;
lastrdata->len = newitemsz;
lastrdata->buffer = buf; /* backup block 1 */
lastrdata->buffer_std = true;
}
else
{
lastrdata->data = NULL;
lastrdata->len = 0;
lastrdata->buffer = buf; /* backup block 1 */
lastrdata->buffer_std = true;
}
/* Log the contents of the right page in the format understood by
* _bt_restore_page(). We set lastrdata->buffer to InvalidBuffer,
* because we're going to recreate the whole page anyway.
*
* Direct access to page is not good but faster - we should implement
* some new func in page API. Note we only store the tuples
* themselves, knowing that the item pointers are in the same order
* and can be reconstructed by scanning the tuples. See comments for
* _bt_restore_page().
*/
xlrec.leftlen = ((PageHeader) leftpage)->pd_special -
((PageHeader) leftpage)->pd_upper;
lastrdata->next = lastrdata + 1;
lastrdata++;
rdata[0].data = (char *) &xlrec;
rdata[0].len = SizeOfBtreeSplit;
rdata[0].buffer = InvalidBuffer;
rdata[0].next = &(rdata[1]);
rdata[1].data = (char *) leftpage + ((PageHeader) leftpage)->pd_upper;
rdata[1].len = xlrec.leftlen;
rdata[1].buffer = InvalidBuffer;
rdata[1].next = &(rdata[2]);
rdata[2].data = (char *) rightpage + ((PageHeader) rightpage)->pd_upper;
rdata[2].len = ((PageHeader) rightpage)->pd_special -
lastrdata->data = (char *) rightpage +
((PageHeader) rightpage)->pd_upper;
rdata[2].buffer = InvalidBuffer;
rdata[2].next = NULL;
lastrdata->len = ((PageHeader) rightpage)->pd_special -
((PageHeader) rightpage)->pd_upper;
lastrdata->buffer = InvalidBuffer;
/* Log the right sibling, because we've changed it's prev-pointer. */
if (!P_RIGHTMOST(ropaque))
{
rdata[2].next = &(rdata[3]);
rdata[3].data = NULL;
rdata[3].len = 0;
rdata[3].buffer = sbuf;
rdata[3].buffer_std = true;
rdata[3].next = NULL;
lastrdata->next = lastrdata + 1;
lastrdata++;
lastrdata->data = NULL;
lastrdata->len = 0;
lastrdata->buffer = sbuf; /* backup block 2 */
lastrdata->buffer_std = true;
}
if (P_ISROOT(oopaque))
lastrdata->next = NULL;
if (isroot)
xlinfo = newitemonleft ? XLOG_BTREE_SPLIT_L_ROOT : XLOG_BTREE_SPLIT_R_ROOT;
else
xlinfo = newitemonleft ? XLOG_BTREE_SPLIT_L : XLOG_BTREE_SPLIT_R;
@ -993,24 +1051,6 @@ _bt_split(Relation rel, Buffer buf, OffsetNumber firstright,
}
}
/*
* By here, the original data page has been split into two new halves, and
* these are correct. The algorithm requires that the left page never
* move during a split, so we copy the new left page back on top of the
* original. Note that this is not a waste of time, since we also require
* (in the page management code) that the center of a page always be
* clean, and the most efficient way to guarantee this is just to compact
* the data by reinserting it into a new left page. (XXX the latter
* comment is probably obsolete.)
*
* It's a bit weird that we don't fill in the left page till after writing
* the XLOG entry, but not really worth changing. Note that we use the
* origpage data (specifically its BTP_ROOT bit) while preparing the XLOG
* entry, so simply reshuffling the code won't do.
*/
PageRestoreTempPage(leftpage, origpage);
END_CRIT_SECTION();
/* release the old right sibling */