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During WAL recovery, when reading a page that we intend to overwrite completely

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from the WAL data, don't bother to physically read it; just have bufmgr.c
return a zeroed-out buffer instead.  This speeds recovery significantly,
and also avoids unnecessary failures when a page-to-be-overwritten has corrupt
page headers on disk.  This replaces a former kluge that accomplished the
latter by pretending zero_damaged_pages was always ON during WAL recovery;
which was OK when the kluge was put in, but is unsafe when restoring a WAL
log that was written with full_page_writes off.

Heikki Linnakangas
This commit is contained in:
Tom Lane
2007-05-02 23:18:03 +00:00
parent 8ec943856a
commit 8c3cc86e7b
3 changed files with 49 additions and 13 deletions
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11
src/backend/access/transam/xlogutils.c
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@ -11,7 +11,7 @@
* Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/backend/access/transam/xlogutils.c,v 1.49 2007/01/05 22:19:24 momjian Exp $
* $PostgreSQL: pgsql/src/backend/access/transam/xlogutils.c,v 1.50 2007/05/02 23:18:03 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -206,7 +206,9 @@ XLogCheckInvalidPages(void)
* If "init" is true then the caller intends to rewrite the page fully
* using the info in the XLOG record. In this case we will extend the
* relation if needed to make the page exist, and we will not complain about
* the page being "new" (all zeroes).
* the page being "new" (all zeroes); in fact, we usually will supply a
* zeroed buffer without reading the page at all, so as to avoid unnecessary
* failure if the page is present on disk but has corrupt headers.
*
* If "init" is false then the caller needs the page to be valid already.
* If the page doesn't exist or contains zeroes, we return InvalidBuffer.
@ -226,7 +228,10 @@ XLogReadBuffer(Relation reln, BlockNumber blkno, bool init)
if (blkno < lastblock)
{
/* page exists in file */
buffer = ReadBuffer(reln, blkno);
if (init)
buffer = ReadOrZeroBuffer(reln, blkno);
else
buffer = ReadBuffer(reln, blkno);
}
else
{