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Commit04d9f4d

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Improve pg_dump's checkSeek() function to verify the functioning of ftello
as well as fseeko, and to not assume that fseeko(fp, 0, SEEK_CUR) provesanything. Also improve some related comments. Per my observation thatthe SEEK_CUR test didn't actually work on some platforms, and subsequentdiscussion with Robert Haas.Back-patch to 8.4. In earlier releases it's not that important whetherwe get the hasSeek test right, but with parallel restore it matters.
1 parentb779ea8 commit04d9f4d

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2 files changed

+44
-23
lines changed

2 files changed

+44
-23
lines changed

‎src/bin/pg_dump/pg_backup_archiver.c

Lines changed: 37 additions & 18 deletions
Original file line numberDiff line numberDiff line change
@@ -15,7 +15,7 @@
1515
*
1616
*
1717
* IDENTIFICATION
18-
*$PostgreSQL: pgsql/src/bin/pg_dump/pg_backup_archiver.c,v 1.185 2010/05/15 21:41:16 tgl Exp $
18+
*$PostgreSQL: pgsql/src/bin/pg_dump/pg_backup_archiver.c,v 1.186 2010/06/28 02:07:02 tgl Exp $
1919
*
2020
*-------------------------------------------------------------------------
2121
*/
@@ -1755,6 +1755,11 @@ _discoverArchiveFormat(ArchiveHandle *AH)
17551755

17561756
if (strncmp(sig,"PGDMP",5)==0)
17571757
{
1758+
/*
1759+
* Finish reading (most of) a custom-format header.
1760+
*
1761+
* NB: this code must agree with ReadHead().
1762+
*/
17581763
AH->vmaj=fgetc(fh);
17591764
AH->vmin=fgetc(fh);
17601765

@@ -2981,7 +2986,12 @@ ReadHead(ArchiveHandle *AH)
29812986
intfmt;
29822987
structtmcrtm;
29832988

2984-
/* If we haven't already read the header... */
2989+
/*
2990+
* If we haven't already read the header, do so.
2991+
*
2992+
* NB: this code must agree with _discoverArchiveFormat(). Maybe find
2993+
* a way to unify the cases?
2994+
*/
29852995
if (!AH->readHeader)
29862996
{
29872997
if ((*AH->ReadBufPtr) (AH,tmpMag,5)!=5)
@@ -3000,7 +3010,6 @@ ReadHead(ArchiveHandle *AH)
30003010

30013011
AH->version= ((AH->vmaj*256+AH->vmin)*256+AH->vrev)*256+0;
30023012

3003-
30043013
if (AH->version<K_VERS_1_0||AH->version>K_VERS_MAX)
30053014
die_horribly(AH,modulename,"unsupported version (%d.%d) in file header\n",
30063015
AH->vmaj,AH->vmin);
@@ -3068,27 +3077,37 @@ ReadHead(ArchiveHandle *AH)
30683077

30693078
/*
30703079
* checkSeek
3071-
* check to see if fseek can be performed.
3080+
* check to see ifftell/fseek can be performed.
30723081
*/
30733082
bool
30743083
checkSeek(FILE*fp)
30753084
{
3076-
if (fseeko(fp,0,SEEK_CUR)!=0)
3077-
return false;
3078-
elseif (sizeof(pgoff_t)>sizeof(long))
3079-
{
3080-
/*
3081-
* At this point, pgoff_t is too large for long, so we return based on
3082-
* whether an pgoff_t version of fseek is available.
3083-
*/
3084-
#ifdefHAVE_FSEEKO
3085-
return true;
3086-
#else
3085+
pgoff_ttpos;
3086+
3087+
/*
3088+
* If pgoff_t is wider than long, we must have "real" fseeko and not
3089+
* an emulation using fseek. Otherwise report no seek capability.
3090+
*/
3091+
#ifndefHAVE_FSEEKO
3092+
if (sizeof(pgoff_t)>sizeof(long))
30873093
return false;
30883094
#endif
3089-
}
3090-
else
3091-
return true;
3095+
3096+
/* Check that ftello works on this file */
3097+
errno=0;
3098+
tpos=ftello(fp);
3099+
if (errno)
3100+
return false;
3101+
3102+
/*
3103+
* Check that fseeko(SEEK_SET) works, too. NB: we used to try to test
3104+
* this with fseeko(fp, 0, SEEK_CUR). But some platforms treat that as a
3105+
* successful no-op even on files that are otherwise unseekable.
3106+
*/
3107+
if (fseeko(fp,tpos,SEEK_SET)!=0)
3108+
return false;
3109+
3110+
return true;
30923111
}
30933112

30943113

‎src/bin/pg_dump/pg_backup_custom.c

Lines changed: 7 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -19,7 +19,7 @@
1919
*
2020
*
2121
* IDENTIFICATION
22-
*$PostgreSQL: pgsql/src/bin/pg_dump/pg_backup_custom.c,v 1.45 2010/06/27 19:07:24 tgl Exp $
22+
*$PostgreSQL: pgsql/src/bin/pg_dump/pg_backup_custom.c,v 1.46 2010/06/28 02:07:02 tgl Exp $
2323
*
2424
*-------------------------------------------------------------------------
2525
*/
@@ -835,9 +835,10 @@ _CloseArchive(ArchiveHandle *AH)
835835
WriteDataChunks(AH);
836836

837837
/*
838-
* This is not an essential operation - it is really only needed if we
839-
* expect to be doing seeks to read the data back - it may be ok to
840-
* just use the existing self-consistent block formatting.
838+
* If possible, re-write the TOC in order to update the data offset
839+
* information. This is not essential, as pg_restore can cope in
840+
* most cases without it; but it can make pg_restore significantly
841+
* faster in some situations (especially parallel restore).
841842
*/
842843
if (ctx->hasSeek&&
843844
fseeko(AH->FH,tpos,SEEK_SET)==0)
@@ -914,7 +915,8 @@ _getFilePos(ArchiveHandle *AH, lclContext *ctx)
914915

915916
/*
916917
* Prior to 1.7 (pg7.3) we relied on the internally maintained
917-
* pointer. Now we rely on pgoff_t always. pos = ctx->filePos;
918+
* pointer. Now we rely on ftello() always, unless the file has
919+
* been found to not support it.
918920
*/
919921
}
920922
}

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