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Commit403a3d9

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pg_dump: Lock all relations, not just plain tables
Now that LOCK TABLE can take any relation type, acquire lock on allrelations that are to be dumped. This prevents schema changes ordeadlock errors that could cause a dump to fail after expending mucheffort. The server is tested to have the capability and the featuredisabled if it doesn't, so that a patched pg_dump doesn't fail whenconnecting to an unpatched server.Backpatch to 9.5.Author: Álvaro Herrera <alvherre@alvh.no-ip.org>Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>Reported-by: Wells Oliver <wells.oliver@gmail.com>Discussion:https://postgr.es/m/20201021200659.GA32358@alvherre.pgsql
1 parentf893e68 commit403a3d9

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4 files changed

+78
-7
lines changed

4 files changed

+78
-7
lines changed

‎src/bin/pg_dump/pg_backup.h

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -198,6 +198,8 @@ typedef struct Archive
198198
intminRemoteVersion;/* allowable range */
199199
intmaxRemoteVersion;
200200

201+
boolhasGenericLockTable;/* can LOCK TABLE do non-table rels */
202+
201203
intnumWorkers;/* number of parallel processes */
202204
char*sync_snapshot_id;/* sync snapshot id for parallel operation */
203205

‎src/bin/pg_dump/pg_backup_db.c

Lines changed: 64 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -531,6 +531,70 @@ EndDBCopyMode(Archive *AHX, const char *tocEntryTag)
531531
}
532532
}
533533

534+
/*
535+
* Does LOCK TABLE work on non-table relations on this server?
536+
*
537+
* Note: assumes it is called out of any transaction
538+
*/
539+
bool
540+
IsLockTableGeneric(Archive*AHX)
541+
{
542+
ArchiveHandle*AH= (ArchiveHandle*)AHX;
543+
PGresult*res;
544+
char*sqlstate;
545+
boolretval;
546+
547+
if (AHX->remoteVersion >=140000)
548+
return true;
549+
elseif (AHX->remoteVersion<90500)
550+
return false;
551+
552+
StartTransaction(AHX);
553+
554+
/*
555+
* Try a LOCK TABLE on a well-known non-table catalog; WRONG_OBJECT_TYPE
556+
* tells us that this server doesn't support locking non-table rels, while
557+
* LOCK_NOT_AVAILABLE and INSUFFICIENT_PRIVILEGE tell us that it does.
558+
* Report anything else as a fatal problem.
559+
*/
560+
#defineERRCODE_INSUFFICIENT_PRIVILEGE"42501"
561+
#defineERRCODE_WRONG_OBJECT_TYPE"42809"
562+
#defineERRCODE_LOCK_NOT_AVAILABLE"55P03"
563+
res=PQexec(AH->connection,
564+
"LOCK TABLE pg_catalog.pg_class_tblspc_relfilenode_index IN ACCESS SHARE MODE NOWAIT");
565+
switch (PQresultStatus(res))
566+
{
567+
casePGRES_COMMAND_OK:
568+
retval= true;
569+
break;
570+
casePGRES_FATAL_ERROR:
571+
sqlstate=PQresultErrorField(res,PG_DIAG_SQLSTATE);
572+
if (strcmp(sqlstate,ERRCODE_WRONG_OBJECT_TYPE)==0)
573+
{
574+
retval= false;
575+
break;
576+
}
577+
elseif (strcmp(sqlstate,ERRCODE_LOCK_NOT_AVAILABLE)==0||
578+
strcmp(sqlstate,ERRCODE_INSUFFICIENT_PRIVILEGE)==0)
579+
{
580+
retval= true;
581+
break;
582+
}
583+
/* else, falls through */
584+
default:
585+
warn_or_exit_horribly(AH,"LOCK TABLE failed for \"%s\": %s",
586+
"pg_catalog.pg_class_tblspc_relfilenode_index",
587+
PQerrorMessage(AH->connection));
588+
retval= false;/* not reached */
589+
break;
590+
}
591+
PQclear(res);
592+
593+
CommitTransaction(AHX);
594+
595+
returnretval;
596+
}
597+
534598
void
535599
StartTransaction(Archive*AHX)
536600
{

‎src/bin/pg_dump/pg_backup_db.h

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -20,6 +20,8 @@ extern PGresult *ExecuteSqlQueryForSingleRow(Archive *fout, const char *query);
2020

2121
externvoidEndDBCopyMode(Archive*AHX,constchar*tocEntryTag);
2222

23+
externboolIsLockTableGeneric(Archive*AHX);
24+
2325
externvoidStartTransaction(Archive*AHX);
2426
externvoidCommitTransaction(Archive*AHX);
2527

‎src/bin/pg_dump/pg_dump.c

Lines changed: 10 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -1176,6 +1176,9 @@ setup_connection(Archive *AH, const char *dumpencoding,
11761176
ExecuteSqlStatement(AH, "SET row_security = off");
11771177
}
11781178

1179+
/* Detect whether LOCK TABLE can handle non-table relations */
1180+
AH->hasGenericLockTable = IsLockTableGeneric(AH);
1181+
11791182
/*
11801183
* Start transaction-snapshot mode transaction to dump consistent data.
11811184
*/
@@ -6843,16 +6846,16 @@ getTables(Archive *fout, int *numTables)
68436846
* assume our lock on the child is enough to prevent schema
68446847
* alterations to parent tables.
68456848
*
6846-
* NOTE: it'd be kinda nice to lock other relations too, not only
6847-
* plain or partitioned tables, but the backend doesn't presently
6848-
* allow that.
6849-
*
6850-
* We only need to lock the table for certain components; see
6849+
* We only need to lock the relation for certain components; see
68516850
* pg_dump.h
6851+
*
6852+
* On server versions that support it, we lock all relations not just
6853+
* plain tables.
68526854
*/
68536855
if (tblinfo[i].dobj.dump &&
6854-
(tblinfo[i].relkind == RELKIND_RELATION ||
6855-
tblinfo->relkind == RELKIND_PARTITIONED_TABLE) &&
6856+
(fout->hasGenericLockTable ||
6857+
tblinfo[i].relkind == RELKIND_PARTITIONED_TABLE ||
6858+
tblinfo[i].relkind == RELKIND_RELATION) &&
68566859
(tblinfo[i].dobj.dump & DUMP_COMPONENTS_REQUIRING_LOCK))
68576860
{
68586861
resetPQExpBuffer(query);

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