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Commit984d56b

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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 parent5b48e2e commit984d56b

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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 @@
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*
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.336 2010/07/2911:06:34 sriggs Exp $
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* $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.337 2010/07/2919:23:20 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
@@ -7230,11 +7230,20 @@ static void
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copy_relation_data(SMgrRelationsrc,SMgrRelationdst,
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ForkNumberforkNum,boolistemp)
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{
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char*buf;
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Pagepage;
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booluse_wal;
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BlockNumbernblocks;
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BlockNumberblkno;
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charbuf[BLCKSZ];
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Pagepage= (Page)buf;
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/*
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* palloc the buffer so that it's MAXALIGN'd. If it were just a local
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* 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
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* mention possibly making log_newpage's accesses to the page header fail.
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*/
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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/streaming is
@@ -7263,6 +7272,8 @@ copy_relation_data(SMgrRelation src, SMgrRelation dst,
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smgrextend(dst,forkNum,blkno,buf, true);
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}
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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 safe
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* to commit the transaction. (For a temp rel we don't care since the rel

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