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Code review for btree page split WAL reduction patch. Make it actually work

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(original code *always* created a full-page image for the left page, thus
leaving the intended savings unrealized), avoid risk of not having enough room
on the page during xlog restore, squeeze out another couple bytes in the xlog
record, clean up neglected comments.
This commit is contained in:
Tom Lane
2007-04-11 20:47:38 +00:00
parent f7424b0d4b
commit 226a100568
4 changed files with 166 additions and 126 deletions
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107
src/backend/access/nbtree/nbtinsert.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/access/nbtree/nbtinsert.c,v 1.155 2007/03/25 19:45:14 tgl Exp $
* $PostgreSQL: pgsql/src/backend/access/nbtree/nbtinsert.c,v 1.156 2007/04/11 20:47:37 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -49,7 +49,7 @@ static TransactionId _bt_check_unique(Relation rel, IndexTuple itup,
Relation heapRel, Buffer buf, OffsetNumber ioffset,
ScanKey itup_scankey);
static void _bt_findinsertloc(Relation rel,
Buffer *bufptr,
Buffer *bufptr,
OffsetNumber *offsetptr,
int keysz,
ScanKey scankey,
@ -66,7 +66,7 @@ static OffsetNumber _bt_findsplitloc(Relation rel, Page page,
OffsetNumber newitemoff,
Size newitemsz,
bool *newitemonleft);
static void _bt_checksplitloc(FindSplitData *state,
static void _bt_checksplitloc(FindSplitData *state,
OffsetNumber firstoldonright, bool newitemonleft,
int dataitemstoleft, Size firstoldonrightsz);
static void _bt_pgaddtup(Relation rel, Page page,
@ -459,7 +459,7 @@ _bt_findinsertloc(Relation rel,
* the hint supplied by the caller invalid */
vacuumed = true;
if (PageGetFreeSpace(page) >= itemsz)
if (PageGetFreeSpace(page) >= itemsz)
break; /* OK, now we have enough space */
}
@ -506,7 +506,7 @@ _bt_findinsertloc(Relation rel,
* moved right at all, we know we should insert at the start of the
* page. If we didn't move right, we can use the firstlegaloff hint
* if the caller supplied one, unless we vacuumed the page which
* might have moved tuples around making the hint invalid. If we
* might have moved tuples around making the hint invalid. If we
* didn't move right or can't use the hint, find the position
* by searching.
*/
@ -779,8 +779,6 @@ _bt_split(Relation rel, Buffer buf, OffsetNumber firstright,
Buffer sbuf = InvalidBuffer;
Page spage = NULL;
BTPageOpaque sopaque = NULL;
OffsetNumber itup_off = 0;
BlockNumber itup_blkno = 0;
Size itemsz;
ItemId itemid;
IndexTuple item;
@ -798,6 +796,14 @@ _bt_split(Relation rel, Buffer buf, OffsetNumber firstright,
_bt_pageinit(leftpage, BufferGetPageSize(buf));
/* rightpage was already initialized by _bt_getbuf */
/*
* Copy the original page's LSN and TLI into leftpage, which will become
* the updated version of the page. We need this because XLogInsert will
* examine these fields and possibly dump them in a page image.
*/
PageSetLSN(leftpage, PageGetLSN(origpage));
PageSetTLI(leftpage, PageGetTLI(origpage));
/* init btree private data */
oopaque = (BTPageOpaque) PageGetSpecialPointer(origpage);
lopaque = (BTPageOpaque) PageGetSpecialPointer(leftpage);
@ -864,7 +870,10 @@ _bt_split(Relation rel, Buffer buf, OffsetNumber firstright,
leftoff = OffsetNumberNext(leftoff);
/*
* Now transfer all the data items to the appropriate page
* Now transfer all the data items to the appropriate page.
*
* Note: we *must* insert at least the right page's items in item-number
* order, for the benefit of _bt_restore_page().
*/
maxoff = PageGetMaxOffsetNumber(origpage);
@ -881,16 +890,12 @@ _bt_split(Relation rel, Buffer buf, OffsetNumber firstright,
{
_bt_pgaddtup(rel, leftpage, newitemsz, newitem, leftoff,
"left sibling");
itup_off = leftoff;
itup_blkno = BufferGetBlockNumber(buf);
leftoff = OffsetNumberNext(leftoff);
}
else
{
_bt_pgaddtup(rel, rightpage, newitemsz, newitem, rightoff,
"right sibling");
itup_off = rightoff;
itup_blkno = BufferGetBlockNumber(rbuf);
rightoff = OffsetNumberNext(rightoff);
}
}
@ -921,8 +926,6 @@ _bt_split(Relation rel, Buffer buf, OffsetNumber firstright,
Assert(!newitemonleft);
_bt_pgaddtup(rel, rightpage, newitemsz, newitem, rightoff,
"right sibling");
itup_off = rightoff;
itup_blkno = BufferGetBlockNumber(rbuf);
rightoff = OffsetNumberNext(rightoff);
}
@ -961,7 +964,7 @@ _bt_split(Relation rel, Buffer buf, OffsetNumber firstright,
/*
* Right sibling is locked, new siblings are prepared, but original page
* is not updated yet. Log changes before continuing.
* is not updated yet.
*
* NO EREPORT(ERROR) till right sibling is updated. We can get away with
* not starting the critical section till here because we haven't been
@ -970,15 +973,6 @@ _bt_split(Relation rel, Buffer buf, OffsetNumber firstright,
*/
START_CRIT_SECTION();
MarkBufferDirty(buf);
MarkBufferDirty(rbuf);
if (!P_RIGHTMOST(ropaque))
{
sopaque->btpo_prev = BufferGetBlockNumber(rbuf);
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
@ -994,6 +988,15 @@ _bt_split(Relation rel, Buffer buf, OffsetNumber firstright,
*/
PageRestoreTempPage(leftpage, origpage);
MarkBufferDirty(buf);
MarkBufferDirty(rbuf);
if (!P_RIGHTMOST(ropaque))
{
sopaque->btpo_prev = BufferGetBlockNumber(rbuf);
MarkBufferDirty(sbuf);
}
/* XLOG stuff */
if (!rel->rd_istemp)
{
@ -1006,9 +1009,9 @@ _bt_split(Relation rel, Buffer buf, OffsetNumber firstright,
xlrec.node = rel->rd_node;
xlrec.leftsib = BufferGetBlockNumber(buf);
xlrec.rightsib = BufferGetBlockNumber(rbuf);
xlrec.firstright = firstright;
xlrec.rnext = ropaque->btpo_next;
xlrec.level = ropaque->btpo.level;
xlrec.firstright = firstright;
rdata[0].data = (char *) &xlrec;
rdata[0].len = SizeOfBtreeSplit;
@ -1027,14 +1030,18 @@ _bt_split(Relation rel, Buffer buf, OffsetNumber firstright,
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.
/*
* Log the new item and its offset, 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.) Show these as belonging to the left page buffer,
* so that they are not stored if XLogInsert decides it needs a
* full-page image of the left page.
*/
lastrdata->next = lastrdata + 1;
lastrdata++;
if (newitemonleft)
{
lastrdata->next = lastrdata + 1;
lastrdata++;
lastrdata->data = (char *) &newitemoff;
lastrdata->len = sizeof(OffsetNumber);
lastrdata->buffer = buf; /* backup block 1 */
@ -1042,39 +1049,49 @@ _bt_split(Relation rel, Buffer buf, OffsetNumber firstright,
lastrdata->next = lastrdata + 1;
lastrdata++;
lastrdata->data = (char *)newitem;
lastrdata->len = newitemsz;
lastrdata->data = (char *) newitem;
lastrdata->len = MAXALIGN(newitemsz);
lastrdata->buffer = buf; /* backup block 1 */
lastrdata->buffer_std = true;
}
else
{
/*
* Although we don't need to WAL-log the new item, we still
* need XLogInsert to consider storing a full-page image of the
* left page, so make an empty entry referencing that buffer.
* This also ensures that the left page is always backup block 1.
*/
lastrdata->next = lastrdata + 1;
lastrdata++;
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
/*
* 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.
* because we're going to recreate the whole page anyway, so it
* should never be stored by XLogInsert.
*
* 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
* themselves, knowing that they were inserted in item-number order
* and so the item pointers can be reconstructed. See comments for
* _bt_restore_page().
*/
lastrdata->next = lastrdata + 1;
lastrdata++;
lastrdata->data = (char *) rightpage +
lastrdata->data = (char *) rightpage +
((PageHeader) rightpage)->pd_upper;
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. */
/* Log the right sibling, because we've changed its' prev-pointer. */
if (!P_RIGHTMOST(ropaque))
{
lastrdata->next = lastrdata + 1;
@ -1216,7 +1233,7 @@ _bt_findsplitloc(Relation rel,
olddataitemstoleft = 0;
goodenoughfound = false;
maxoff = PageGetMaxOffsetNumber(page);
for (offnum = P_FIRSTDATAKEY(opaque);
offnum <= maxoff;
offnum = OffsetNumberNext(offnum))
@ -1234,7 +1251,7 @@ _bt_findsplitloc(Relation rel,
olddataitemstoleft, itemsz);
else if (offnum < newitemoff)
_bt_checksplitloc(&state, offnum, false,
_bt_checksplitloc(&state, offnum, false,
olddataitemstoleft, itemsz);
else
{
@ -1285,11 +1302,11 @@ _bt_findsplitloc(Relation rel,
* items go to the left page and only the new item goes to the right page.
* In that case, firstoldonrightsz is not used.
*
* olddataitemstoleft is the total size of all old items to the left of
* firstoldonright.
* olddataitemstoleft is the total size of all old items to the left of
* firstoldonright.
*/
static void
_bt_checksplitloc(FindSplitData *state,
_bt_checksplitloc(FindSplitData *state,
OffsetNumber firstoldonright,
bool newitemonleft,
int olddataitemstoleft,
@ -1311,7 +1328,7 @@ _bt_checksplitloc(FindSplitData *state,
/* Account for all the old tuples */
leftfree = state->leftspace - olddataitemstoleft;
rightfree = state->rightspace -
rightfree = state->rightspace -
(state->olddataitemstotal - olddataitemstoleft);
/*
@ -1854,7 +1871,7 @@ _bt_vacuum_one_page(Relation rel, Buffer buffer)
BTPageOpaque opaque = (BTPageOpaque) PageGetSpecialPointer(page);
/*
* Scan over all items to see which ones need to be deleted
* Scan over all items to see which ones need to be deleted
* according to LP_DELETE flags.
*/
minoff = P_FIRSTDATAKEY(opaque);