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Fix another longstanding problem in copy_relation_data: it was blithely

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assuming that a local char[] array would be aligned on at least a word
boundary.  There are architectures on which that is pretty much guaranteed to
NOT be the case ... and those arches also don't like non-aligned memory
accesses, meaning that log_newpage() would crash if it ever got invoked.
Even on Intel-ish machines there's a potential for a large performance penalty
from doing I/O to an inadequately aligned buffer.  So palloc it instead.

Backpatch to 8.0 --- 7.4 doesn't have this code.
This commit is contained in:
Tom Lane 2010-07-29 19:24:05 +00:00
parent 3137b49698
commit 8e21bf5250
1 changed files with 14 additions and 3 deletions
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17
src/backend/commands/tablecmds.c
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@ -8,7 +8,7 @@
* *
* *
* IDENTIFICATION * IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.142.4.13 2010/07/29 16:15:47 rhaas Exp $ * $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.142.4.14 2010/07/29 19:24:05 tgl Exp $
* *
*------------------------------------------------------------------------- *-------------------------------------------------------------------------
*/ */
@ -5729,11 +5729,11 @@ static void
copy_relation_data(Relation rel, SMgrRelation dst) copy_relation_data(Relation rel, SMgrRelation dst)
{ {
SMgrRelation src; SMgrRelation src;
char *buf;
Page page;
bool use_wal; bool use_wal;
BlockNumber nblocks; BlockNumber nblocks;
BlockNumber blkno; BlockNumber blkno;
char buf[BLCKSZ];
Page page = (Page) buf;
/* /*
* Since we copy the data directly without looking at the shared * Since we copy the data directly without looking at the shared
@ -5744,6 +5744,15 @@ copy_relation_data(Relation rel, SMgrRelation dst)
*/ */
FlushRelationBuffers(rel, 0); FlushRelationBuffers(rel, 0);
/*
* palloc the buffer so that it's MAXALIGN'd. If it were just a local
* char[] array, the compiler might align it on any byte boundary, which
* can seriously hurt transfer speed to and from the kernel; not to
* mention possibly making PageSetLSN fail.
*/
buf = (char *) palloc(BLCKSZ);
page = (Page) buf;
/* /*
* We need to log the copied data in WAL iff WAL archiving is enabled * We need to log the copied data in WAL iff WAL archiving is enabled
* AND it's not a temp rel. * AND it's not a temp rel.
@ -5807,6 +5816,8 @@ copy_relation_data(Relation rel, SMgrRelation dst)
smgrwrite(dst, blkno, buf, true); smgrwrite(dst, blkno, buf, true);
} }
pfree(buf);
/* /*
* If the rel isn't temp, we must fsync it down to disk before it's * If the rel isn't temp, we must fsync it down to disk before it's
* safe to commit the transaction. (For a temp rel we don't care * safe to commit the transaction. (For a temp rel we don't care