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Commit14bc951

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Fix low-probability bug in relcache startup: write_irels wrote the
pg_internal.init file in-place, which meant that if another backendstarted at about the same time, it might read the incomplete file.init_irels tries to guard against that, but I have now seen a crashdue to reading bad data from a partly-written file. (This may indicatea kernel bug on my platform? Not sure.) Anyway, clearly the safestcourse is to write the new pg_internal.init file under a unique temporaryfilename, and rename it into place only after it's all written.
1 parentdbc9346 commit14bc951

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‎src/backend/utils/cache/relcache.c‎

Lines changed: 23 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $Header: /cvsroot/pgsql/src/backend/utils/cache/relcache.c,v 1.93 2000/03/17 02:36:27 tgl Exp $
11+
* $Header: /cvsroot/pgsql/src/backend/utils/cache/relcache.c,v 1.94 2000/03/31 19:39:22 tgl Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -33,6 +33,7 @@
3333
#include<errno.h>
3434
#include<sys/file.h>
3535
#include<fcntl.h>
36+
#include<unistd.h>
3637

3738
#include"postgres.h"
3839

@@ -2266,14 +2267,26 @@ write_irels(void)
22662267
inti;
22672268
intrelno;
22682269
RelationBuildDescInfobi;
2270+
chartempfilename[MAXPGPATH];
2271+
charfinalfilename[MAXPGPATH];
2272+
2273+
/*
2274+
* We must write a temporary file and rename it into place. Otherwise,
2275+
* another backend starting at about the same time might crash trying to
2276+
* read the partially-complete file.
2277+
*/
2278+
snprintf(tempfilename,sizeof(tempfilename),"%s%c%s.%d",
2279+
DatabasePath,SEP_CHAR,RELCACHE_INIT_FILENAME,MyProcPid);
2280+
snprintf(finalfilename,sizeof(finalfilename),"%s%c%s",
2281+
DatabasePath,SEP_CHAR,RELCACHE_INIT_FILENAME);
22692282

22702283
#ifndef__CYGWIN32__
2271-
fd=FileNameOpenFile(RELCACHE_INIT_FILENAME,O_WRONLY |O_CREAT |O_TRUNC,0600);
2284+
fd=PathNameOpenFile(tempfilename,O_WRONLY |O_CREAT |O_TRUNC,0600);
22722285
#else
2273-
fd=FileNameOpenFile(RELCACHE_INIT_FILENAME,O_WRONLY |O_CREAT |O_TRUNC |O_BINARY,0600);
2286+
fd=PathNameOpenFile(tempfilename,O_WRONLY |O_CREAT |O_TRUNC |O_BINARY,0600);
22742287
#endif
22752288
if (fd<0)
2276-
elog(FATAL,"cannot create init file %s",RELCACHE_INIT_FILENAME);
2289+
elog(FATAL,"cannot create init file %s",tempfilename);
22772290

22782291
FileSeek(fd,0L,SEEK_SET);
22792292

@@ -2397,4 +2410,10 @@ write_irels(void)
23972410
}
23982411

23992412
FileClose(fd);
2413+
2414+
/*
2415+
* And rename the temp file to its final name, deleting any previously-
2416+
* existing init file.
2417+
*/
2418+
rename(tempfilename,finalfilename);
24002419
}

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