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Commit d74048d

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Make pg_dump error cleanly with -j against hot standby
Getting a synchronized snapshot is not supported on a hot standby node, and is by default taken when using -j with multiple sessions. Trying to do so still failed, but with a server error that would also go in the log. Instead, proprely detect this case and give a better error message.
1 parent aeb9ae6 commit d74048d

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4 files changed

+53
-40
lines changed

4 files changed

+53
-40
lines changed

src/bin/pg_dump/pg_backup.h

+1
Original file line numberDiff line numberDiff line change
@@ -173,6 +173,7 @@ typedef struct Archive
173173
int verbose;
174174
char *remoteVersionStr; /* server's version string */
175175
int remoteVersion; /* same in numeric form */
176+
bool isStandby; /* is server a standby node */
176177

177178
int minRemoteVersion; /* allowable range */
178179
int maxRemoteVersion;

src/bin/pg_dump/pg_backup_db.c

+38
Original file line numberDiff line numberDiff line change
@@ -37,6 +37,7 @@ _check_database_version(ArchiveHandle *AH)
3737
{
3838
const char *remoteversion_str;
3939
int remoteversion;
40+
PGresult *res;
4041

4142
remoteversion_str = PQparameterStatus(AH->connection, "server_version");
4243
remoteversion = PQserverVersion(AH->connection);
@@ -56,6 +57,20 @@ _check_database_version(ArchiveHandle *AH)
5657
remoteversion_str, progname, PG_VERSION);
5758
exit_horribly(NULL, "aborting because of server version mismatch\n");
5859
}
60+
61+
/*
62+
* When running against 9.0 or later, check if we are in recovery mode,
63+
* which means we are on a hot standby.
64+
*/
65+
if (remoteversion >= 90000)
66+
{
67+
res = ExecuteSqlQueryForSingleRow((Archive *) AH, "SELECT pg_catalog.pg_is_in_recovery()");
68+
69+
AH->public.isStandby = (strcmp(PQgetvalue(res, 0, 0), "t") == 0);
70+
PQclear(res);
71+
}
72+
else
73+
AH->public.isStandby = false;
5974
}
6075

6176
/*
@@ -388,6 +403,29 @@ ExecuteSqlQuery(Archive *AHX, const char *query, ExecStatusType status)
388403
return res;
389404
}
390405

406+
/*
407+
* Execute an SQL query and verify that we got exactly one row back.
408+
*/
409+
PGresult *
410+
ExecuteSqlQueryForSingleRow(Archive *fout, char *query)
411+
{
412+
PGresult *res;
413+
int ntups;
414+
415+
res = ExecuteSqlQuery(fout, query, PGRES_TUPLES_OK);
416+
417+
/* Expecting a single result only */
418+
ntups = PQntuples(res);
419+
if (ntups != 1)
420+
exit_horribly(NULL,
421+
ngettext("query returned %d row instead of one: %s\n",
422+
"query returned %d rows instead of one: %s\n",
423+
ntups),
424+
ntups, query);
425+
426+
return res;
427+
}
428+
391429
/*
392430
* Convenience function to send a query.
393431
* Monitors result to detect COPY statements

src/bin/pg_dump/pg_backup_db.h

+1
Original file line numberDiff line numberDiff line change
@@ -16,6 +16,7 @@ extern int ExecuteSqlCommandBuf(Archive *AHX, const char *buf, size_t bufLen);
1616
extern void ExecuteSqlStatement(Archive *AHX, const char *query);
1717
extern PGresult *ExecuteSqlQuery(Archive *AHX, const char *query,
1818
ExecStatusType status);
19+
extern PGresult *ExecuteSqlQueryForSingleRow(Archive *fout, char *query);
1920

2021
extern void EndDBCopyMode(Archive *AHX, const char *tocEntryTag);
2122

src/bin/pg_dump/pg_dump.c

+13-40
Original file line numberDiff line numberDiff line change
@@ -264,7 +264,6 @@ static bool nonemptyReloptions(const char *reloptions);
264264
static void appendReloptionsArrayAH(PQExpBuffer buffer, const char *reloptions,
265265
const char *prefix, Archive *fout);
266266
static char *get_synchronized_snapshot(Archive *fout);
267-
static PGresult *ExecuteSqlQueryForSingleRow(Archive *fout, char *query);
268267
static void setupDumpWorker(Archive *AHX);
269268

270269

@@ -657,23 +656,11 @@ main(int argc, char **argv)
657656
dopt.no_security_labels = 1;
658657

659658
/*
660-
* When running against 9.0 or later, check if we are in recovery mode,
661-
* which means we are on a hot standby.
659+
* On hot standby slaves, never try to dump unlogged table data, since it
660+
* will just throw an error.
662661
*/
663-
if (fout->remoteVersion >= 90000)
664-
{
665-
PGresult *res = ExecuteSqlQueryForSingleRow(fout, "SELECT pg_catalog.pg_is_in_recovery()");
666-
667-
if (strcmp(PQgetvalue(res, 0, 0), "t") == 0)
668-
{
669-
/*
670-
* On hot standby slaves, never try to dump unlogged table data,
671-
* since it will just throw an error.
672-
*/
673-
dopt.no_unlogged_table_data = true;
674-
}
675-
PQclear(res);
676-
}
662+
if (fout->isStandby)
663+
dopt.no_unlogged_table_data = true;
677664

678665
/* Select the appropriate subquery to convert user IDs to names */
679666
if (fout->remoteVersion >= 80100)
@@ -1105,7 +1092,16 @@ setup_connection(Archive *AH, const char *dumpencoding,
11051092
else if (AH->numWorkers > 1 &&
11061093
AH->remoteVersion >= 90200 &&
11071094
!dopt->no_synchronized_snapshots)
1095+
{
1096+
if (AH->isStandby)
1097+
exit_horribly(NULL,
1098+
"Synchronized snapshots are not supported on standby servers.\n"
1099+
"Run with --no-synchronized-snapshots instead if you do not need\n"
1100+
"synchronized snapshots.\n");
1101+
1102+
11081103
AH->sync_snapshot_id = get_synchronized_snapshot(AH);
1104+
}
11091105
}
11101106

11111107
static void
@@ -17855,26 +17851,3 @@ appendReloptionsArrayAH(PQExpBuffer buffer, const char *reloptions,
1785517851
if (!res)
1785617852
write_msg(NULL, "WARNING: could not parse reloptions array\n");
1785717853
}
17858-
17859-
/*
17860-
* Execute an SQL query and verify that we got exactly one row back.
17861-
*/
17862-
static PGresult *
17863-
ExecuteSqlQueryForSingleRow(Archive *fout, char *query)
17864-
{
17865-
PGresult *res;
17866-
int ntups;
17867-
17868-
res = ExecuteSqlQuery(fout, query, PGRES_TUPLES_OK);
17869-
17870-
/* Expecting a single result only */
17871-
ntups = PQntuples(res);
17872-
if (ntups != 1)
17873-
exit_horribly(NULL,
17874-
ngettext("query returned %d row instead of one: %s\n",
17875-
"query returned %d rows instead of one: %s\n",
17876-
ntups),
17877-
ntups, query);
17878-
17879-
return res;
17880-
}

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