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pg_dump: Lock all relations, not just plain tables

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Now that LOCK TABLE can take any relation type, acquire lock on all
relations that are to be dumped.  This prevents schema changes or
deadlock errors that could cause a dump to fail after expending much
effort.  The server is tested to have the capability and the feature
disabled if it doesn't, so that a patched pg_dump doesn't fail when
connecting 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
This commit is contained in:
Alvaro Herrera 2020-10-27 14:31:37 -03:00
parent 272bff6a35
commit 64fc3e0349
No known key found for this signature in database
GPG Key ID: 1C20ACB9D5C564AE
4 changed files with 78 additions and 7 deletions
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2
src/bin/pg_dump/pg_backup.h
View File

@ -198,6 +198,8 @@ typedef struct Archive
int minRemoteVersion; /* allowable range */
int maxRemoteVersion;
bool hasGenericLockTable; /* can LOCK TABLE do non-table rels */
int numWorkers; /* number of parallel processes */
char *sync_snapshot_id; /* sync snapshot id for parallel operation */

64
src/bin/pg_dump/pg_backup_db.c
View File

@ -532,6 +532,70 @@ EndDBCopyMode(Archive *AHX, const char *tocEntryTag)
}
}
/*
* Does LOCK TABLE work on non-table relations on this server?
*
* Note: assumes it is called out of any transaction
*/
bool
IsLockTableGeneric(Archive *AHX)
{
ArchiveHandle *AH = (ArchiveHandle *) AHX;
PGresult *res;
char *sqlstate;
bool retval;
if (AHX->remoteVersion >= 140000)
return true;
else if (AHX->remoteVersion < 90500)
return false;
StartTransaction(AHX);
/*
* Try a LOCK TABLE on a well-known non-table catalog; WRONG_OBJECT_TYPE
* tells us that this server doesn't support locking non-table rels, while
* LOCK_NOT_AVAILABLE and INSUFFICIENT_PRIVILEGE tell us that it does.
* Report anything else as a fatal problem.
*/
#define ERRCODE_INSUFFICIENT_PRIVILEGE "42501"
#define ERRCODE_WRONG_OBJECT_TYPE "42809"
#define ERRCODE_LOCK_NOT_AVAILABLE "55P03"
res = PQexec(AH->connection,
"LOCK TABLE pg_catalog.pg_class_tblspc_relfilenode_index IN ACCESS SHARE MODE NOWAIT");
switch (PQresultStatus(res))
{
case PGRES_COMMAND_OK:
retval = true;
break;
case PGRES_FATAL_ERROR:
sqlstate = PQresultErrorField(res, PG_DIAG_SQLSTATE);
if (strcmp(sqlstate, ERRCODE_WRONG_OBJECT_TYPE) == 0)
{
retval = false;
break;
}
else if (strcmp(sqlstate, ERRCODE_LOCK_NOT_AVAILABLE) == 0 ||
strcmp(sqlstate, ERRCODE_INSUFFICIENT_PRIVILEGE) == 0)
{
retval = true;
break;
}
/* else, falls through */
default:
warn_or_exit_horribly(AH, "LOCK TABLE failed for \"%s\": %s",
"pg_catalog.pg_class_tblspc_relfilenode_index",
PQerrorMessage(AH->connection));
retval = false; /* not reached */
break;
}
PQclear(res);
CommitTransaction(AHX);
return retval;
}
void
StartTransaction(Archive *AHX)
{

2
src/bin/pg_dump/pg_backup_db.h
View File

@ -20,6 +20,8 @@ extern PGresult *ExecuteSqlQueryForSingleRow(Archive *fout, const char *query);
extern void EndDBCopyMode(Archive *AHX, const char *tocEntryTag);
extern bool IsLockTableGeneric(Archive *AHX);
extern void StartTransaction(Archive *AHX);
extern void CommitTransaction(Archive *AHX);

17
src/bin/pg_dump/pg_dump.c
View File

@ -1177,6 +1177,9 @@ setup_connection(Archive *AH, const char *dumpencoding,
ExecuteSqlStatement(AH, "SET row_security = off");
}
/* Detect whether LOCK TABLE can handle non-table relations */
AH->hasGenericLockTable = IsLockTableGeneric(AH);
/*
* Start transaction-snapshot mode transaction to dump consistent data.
*/
@ -6840,16 +6843,16 @@ getTables(Archive *fout, int *numTables)
* assume our lock on the child is enough to prevent schema
* alterations to parent tables.
*
* NOTE: it'd be kinda nice to lock other relations too, not only
* plain or partitioned tables, but the backend doesn't presently
* allow that.
*
* We only need to lock the table for certain components; see
* We only need to lock the relation for certain components; see
* pg_dump.h
*
* On server versions that support it, we lock all relations not just
* plain tables.
*/
if (tblinfo[i].dobj.dump &&
(tblinfo[i].relkind == RELKIND_RELATION ||
tblinfo->relkind == RELKIND_PARTITIONED_TABLE) &&
(fout->hasGenericLockTable ||
tblinfo[i].relkind == RELKIND_PARTITIONED_TABLE ||
tblinfo[i].relkind == RELKIND_RELATION) &&
(tblinfo[i].dobj.dump & DUMP_COMPONENTS_REQUIRING_LOCK))
{
resetPQExpBuffer(query);