From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Thu, 29 Jul 2010 19:23:51 +0000 (+0000)
Subject: Fix another longstanding problem in copy_relation_data: it was blithely
X-Git-Tag: REL8_2_18~33
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=a0ad1d1f831d92e9bd94f6e821cc6c85804272e5;p=thirdparty%2Fpostgresql.git

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.
---

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index ec9696e6bbe..48bd6fa4419 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 1.206.2.10 2010/07/29 16:15:18 rhaas Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.206.2.11 2010/07/29 19:23:51 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -6095,11 +6095,11 @@ static void
 copy_relation_data(Relation rel, SMgrRelation dst)
 {
 	SMgrRelation src;
+	char	   *buf;
+	Page		page;
 	bool		use_wal;
 	BlockNumber nblocks;
 	BlockNumber blkno;
-	char		buf[BLCKSZ];
-	Page		page = (Page) buf;
 
 	/*
 	 * Since we copy the file directly without looking at the shared buffers,
@@ -6109,6 +6109,15 @@ copy_relation_data(Relation rel, SMgrRelation dst)
 	 */
 	FlushRelationBuffers(rel);
 
+	/*
+	 * 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 AND
 	 * it's not a temp rel.
@@ -6172,6 +6181,8 @@ copy_relation_data(Relation rel, SMgrRelation dst)
 		smgrwrite(dst, 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