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Fix an ancient oversight in btree xlog replay. When trying to determine if an

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upper-level insertion completes a previously-seen split, we cannot simply grab
the downlink block number out of the buffer, because the buffer could contain
a later state of the page --- or perhaps the page doesn't even exist at all
any more, due to relation truncation.  These possibilities have been masked up
to now because the use of full_page_writes effectively ensured that no xlog
replay routine ever actually saw a page state newer than its own change.
Since we're deprecating full_page_writes in 8.1.*, there's no need to fix this
in existing release branches, but we need a fix in HEAD if we want to have any
hope of re-allowing full_page_writes.  Accordingly, adjust the contents of
btree WAL records so that we can always get the downlink block number from the
WAL record rather than having to depend on buffer contents.  Per report from
Kevin Grittner and Peter Brant.

Improve a few comments in related code while at it.
This commit is contained in:
Tom Lane
2006-04-13 03:53:05 +00:00
parent 3ef151e0b7
commit 49a7610c36
3 changed files with 96 additions and 55 deletions
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42
src/backend/access/nbtree/nbtinsert.c
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@@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/access/nbtree/nbtinsert.c,v 1.134 2006/03/31 23:32:05 tgl Exp $
* $PostgreSQL: pgsql/src/backend/access/nbtree/nbtinsert.c,v 1.135 2006/04/13 03:53:05 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -323,9 +323,9 @@ _bt_check_unique(Relation rel, IndexTuple itup, Relation heapRel,
* child page on the parent.
* + updates the metapage if a true root or fast root is split.
*
* On entry, we must have the right buffer on which to do the
* insertion, and the buffer must be pinned and locked. On return,
* we will have dropped both the pin and the write lock on the buffer.
* On entry, we must have the right buffer in which to do the
* insertion, and the buffer must be pinned and write-locked. On return,
* we will have dropped both the pin and the lock on the buffer.
*
* If 'afteritem' is >0 then the new tuple must be inserted after the
* existing item of that number, noplace else. If 'afteritem' is 0
@@ -527,6 +527,8 @@ _bt_insertonpg(Relation rel,
*/
if (split_only_page)
{
Assert(!P_ISLEAF(lpageop));
metabuf = _bt_getbuf(rel, BTREE_METAPAGE, BT_WRITE);
metapg = BufferGetPage(metabuf);
metad = BTPageGetMeta(metapg);
@@ -557,10 +559,11 @@ _bt_insertonpg(Relation rel,
if (!rel->rd_istemp)
{
xl_btree_insert xlrec;
BlockNumber xldownlink;
xl_btree_metadata xlmeta;
uint8 xlinfo;
XLogRecPtr recptr;
XLogRecData rdata[3];
XLogRecData rdata[4];
XLogRecData *nextrdata;
IndexTupleData trunctuple;
@@ -572,6 +575,22 @@ _bt_insertonpg(Relation rel,
rdata[0].buffer = InvalidBuffer;
rdata[0].next = nextrdata = &(rdata[1]);
if (P_ISLEAF(lpageop))
xlinfo = XLOG_BTREE_INSERT_LEAF;
else
{
xldownlink = ItemPointerGetBlockNumber(&(itup->t_tid));
Assert(ItemPointerGetOffsetNumber(&(itup->t_tid)) == P_HIKEY);
nextrdata->data = (char *) &xldownlink;
nextrdata->len = sizeof(BlockNumber);
nextrdata->buffer = InvalidBuffer;
nextrdata->next = nextrdata + 1;
nextrdata++;
xlinfo = XLOG_BTREE_INSERT_UPPER;
}
if (BufferIsValid(metabuf))
{
xlmeta.root = metad->btm_root;
@@ -584,12 +603,9 @@ _bt_insertonpg(Relation rel,
nextrdata->buffer = InvalidBuffer;
nextrdata->next = nextrdata + 1;
nextrdata++;
xlinfo = XLOG_BTREE_INSERT_META;
}
else if (P_ISLEAF(lpageop))
xlinfo = XLOG_BTREE_INSERT_LEAF;
else
xlinfo = XLOG_BTREE_INSERT_UPPER;
/* Read comments in _bt_pgaddtup */
if (!P_ISLEAF(lpageop) && newitemoff == P_FIRSTDATAKEY(lpageop))
@@ -633,7 +649,7 @@ _bt_insertonpg(Relation rel,
/*
* _bt_split() -- split a page in the btree.
*
* On entry, buf is the page to split, and is write-locked and pinned.
* On entry, buf is the page to split, and is pinned and write-locked.
* firstright is the item index of the first item to be moved to the
* new right page. newitemoff etc. tell us about the new item that
* must be inserted along with the data from the old page.
@@ -860,7 +876,8 @@ _bt_split(Relation rel, Buffer buf, OffsetNumber firstright,
* 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.
* and can be reconstructed by scanning the tuples. See comments
* for _bt_restore_page().
*/
xlrec.leftlen = ((PageHeader) leftpage)->pd_special -
((PageHeader) leftpage)->pd_upper;
@@ -1445,6 +1462,9 @@ _bt_newroot(Relation rel, Buffer lbuf, Buffer rbuf)
* Insert the left page pointer into the new root page. The root page is
* the rightmost page on its level so there is no "high key" in it; the
* two items will go into positions P_HIKEY and P_FIRSTKEY.
*
* Note: we *must* insert the two items in item-number order, for the
* benefit of _bt_restore_page().
*/
if (PageAddItem(rootpage, (Item) new_item, itemsz, P_HIKEY, LP_USED) == InvalidOffsetNumber)
elog(PANIC, "failed to add leftkey to new root page");