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Commit8e21bf5

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Fix another longstanding problem in copy_relation_data: it was blithely
assuming that a local char[] array would be aligned on at least a wordboundary. There are architectures on which that is pretty much guaranteed toNOT be the case ... and those arches also don't like non-aligned memoryaccesses, meaning that log_newpage() would crash if it ever got invoked.Even on Intel-ish machines there's a potential for a large performance penaltyfrom doing I/O to an inadequately aligned buffer. So palloc it instead.Backpatch to 8.0 --- 7.4 doesn't have this code.
1 parent3137b49 commit8e21bf5

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‎src/backend/commands/tablecmds.c

Lines changed: 14 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
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*
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* IDENTIFICATION
11-
* $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.142.4.13 2010/07/2916:15:47 rhaas Exp $
11+
* $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.142.4.14 2010/07/2919:24:05 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
@@ -5729,11 +5729,11 @@ static void
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copy_relation_data(Relationrel,SMgrRelationdst)
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{
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SMgrRelationsrc;
5732+
char*buf;
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Pagepage;
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booluse_wal;
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BlockNumbernblocks;
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BlockNumberblkno;
5735-
charbuf[BLCKSZ];
5736-
Pagepage= (Page)buf;
57375737

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/*
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* Since we copy the data directly without looking at the shared
@@ -5744,6 +5744,15 @@ copy_relation_data(Relation rel, SMgrRelation dst)
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*/
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FlushRelationBuffers(rel,0);
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5747+
/*
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* palloc the buffer so that it's MAXALIGN'd. If it were just a local
5749+
* char[] array, the compiler might align it on any byte boundary, which
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* can seriously hurt transfer speed to and from the kernel; not to
5751+
* mention possibly making PageSetLSN fail.
5752+
*/
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buf= (char*)palloc(BLCKSZ);
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page= (Page)buf;
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/*
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* We need to log the copied data in WAL iff WAL archiving is enabled
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* AND it's not a temp rel.
@@ -5807,6 +5816,8 @@ copy_relation_data(Relation rel, SMgrRelation dst)
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smgrwrite(dst,blkno,buf, true);
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}
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5819+
pfree(buf);
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/*
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* If the rel isn't temp, we must fsync it down to disk before it's
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* safe to commit the transaction.(For a temp rel we don't care

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