From 984d56b80f5a945db2bfa80499b5ed913848242b Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Thu, 29 Jul 2010 19:23:20 +0000
Subject: [PATCH] Fix another longstanding problem in copy_relation_data: it
was blithely 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.
---
src/backend/commands/tablecmds.c | 17 ++++++++++++++---
1 file changed, 14 insertions(+), 3 deletions(-)
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 431b06568bd..b16232a0b52 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.336 2010/07/29 11:06:34 sriggs Exp $
+ * $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.337 2010/07/29 19:23:20 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -7230,11 +7230,20 @@ static void
copy_relation_data(SMgrRelation src, SMgrRelation dst,
ForkNumber forkNum, bool istemp)
{
+ char *buf;
+ Page page;
bool use_wal;
BlockNumber nblocks;
BlockNumber blkno;
- char buf[BLCKSZ];
- Page page = (Page) buf;
+
+ /*
+ * 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 log_newpage's accesses to the page header fail.
+ */
+ buf = (char *) palloc(BLCKSZ);
+ page = (Page) buf;
/*
* We need to log the copied data in WAL iff WAL archiving/streaming is
@@ -7263,6 +7272,8 @@ copy_relation_data(SMgrRelation src, SMgrRelation dst,
smgrextend(dst, forkNum, blkno, buf, true);
}
+ pfree(buf);
+
/*
* 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 since the rel
--
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