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.

diff --git a/src/bin/pg_dump/pg_backup.h b/src/bin/pg_dump/pg_backup.h
index d990c6ccadbca321723441fa60ea62c36c9de33b..45098d985a66cd229ff3cd23fefea4ef1134dec3 100644 (file)
--- a/src/bin/pg_dump/pg_backup.h
+++ b/src/bin/pg_dump/pg_backup.h
@@ -172,6 +172,7 @@ typedef struct Archive
    int         verbose;
    char       *remoteVersionStr;       /* server's version string */
    int         remoteVersion;  /* same in numeric form */
+   bool        isStandby;      /* is server a standby node */
 
    int         minRemoteVersion;       /* allowable range */
    int         maxRemoteVersion;

diff --git a/src/bin/pg_dump/pg_backup_db.c b/src/bin/pg_dump/pg_backup_db.c
index 35ce94592b5c5f10f19094bd4c4013e8b589d611..818bc9efe14a0c04b4678e5fa65b291ae7812c2d 100644 (file)
--- a/src/bin/pg_dump/pg_backup_db.c
+++ b/src/bin/pg_dump/pg_backup_db.c
@@ -37,6 +37,7 @@ _check_database_version(ArchiveHandle *AH)
 {
    const char *remoteversion_str;
    int         remoteversion;
+   PGresult   *res;
 
    remoteversion_str = PQparameterStatus(AH->connection, "server_version");
    remoteversion = PQserverVersion(AH->connection);
@@ -56,6 +57,20 @@ _check_database_version(ArchiveHandle *AH)
                  remoteversion_str, progname, PG_VERSION);
        exit_horribly(NULL, "aborting because of server version mismatch\n");
    }
+
+   /*
+    * When running against 9.0 or later, check if we are in recovery mode,
+    * which means we are on a hot standby.
+    */
+   if (remoteversion >= 90000)
+   {
+       res = ExecuteSqlQueryForSingleRow((Archive *) AH, "SELECT pg_catalog.pg_is_in_recovery()");
+
+       AH->public.isStandby = (strcmp(PQgetvalue(res, 0, 0), "t") == 0);
+       PQclear(res);
+   }
+   else
+       AH->public.isStandby = false;
 }
 
 /*
@@ -388,6 +403,29 @@ ExecuteSqlQuery(Archive *AHX, const char *query, ExecStatusType status)
    return res;
 }
 
+/*
+ * Execute an SQL query and verify that we got exactly one row back.
+ */
+PGresult *
+ExecuteSqlQueryForSingleRow(Archive *fout, char *query)
+{
+   PGresult   *res;
+   int         ntups;
+
+   res = ExecuteSqlQuery(fout, query, PGRES_TUPLES_OK);
+
+   /* Expecting a single result only */
+   ntups = PQntuples(res);
+   if (ntups != 1)
+       exit_horribly(NULL,
+                     ngettext("query returned %d row instead of one: %s\n",
+                              "query returned %d rows instead of one: %s\n",
+                              ntups),
+                     ntups, query);
+
+   return res;
+}
+
 /*
  * Convenience function to send a query.
  * Monitors result to detect COPY statements

diff --git a/src/bin/pg_dump/pg_backup_db.h b/src/bin/pg_dump/pg_backup_db.h
index 6408f144ea127c4a1c650f071d12dfaf5af78c0d..527449e04401314006c00631d81b377663cf1e08 100644 (file)
--- a/src/bin/pg_dump/pg_backup_db.h
+++ b/src/bin/pg_dump/pg_backup_db.h
@@ -16,6 +16,7 @@ extern int    ExecuteSqlCommandBuf(Archive *AHX, const char *buf, size_t bufLen);
 extern void ExecuteSqlStatement(Archive *AHX, const char *query);
 extern PGresult *ExecuteSqlQuery(Archive *AHX, const char *query,
                ExecStatusType status);
+extern PGresult *ExecuteSqlQueryForSingleRow(Archive *fout, char *query);
 
 extern void EndDBCopyMode(Archive *AHX, const char *tocEntryTag);
 

diff --git a/src/bin/pg_dump/pg_dump.c b/src/bin/pg_dump/pg_dump.c
index fa5a7580ef5ab504ee0afc5e8ec858f50c9ce12d..48e650997692188944665c5b8bc44727fc6ae161 100644 (file)
--- a/src/bin/pg_dump/pg_dump.c
+++ b/src/bin/pg_dump/pg_dump.c
@@ -255,7 +255,6 @@ static bool nonemptyReloptions(const char *reloptions);
 static void fmtReloptionsArray(Archive *fout, PQExpBuffer buffer,
                   const char *reloptions, const char *prefix);
 static char *get_synchronized_snapshot(Archive *fout);
-static PGresult *ExecuteSqlQueryForSingleRow(Archive *fout, char *query);
 static void setupDumpWorker(Archive *AHX);
 
 
@@ -647,23 +646,11 @@ main(int argc, char **argv)
        dopt.no_security_labels = 1;
 
    /*
-    * When running against 9.0 or later, check if we are in recovery mode,
-    * which means we are on a hot standby.
+    * On hot standby slaves, never try to dump unlogged table data, since it
+    * will just throw an error.
     */
-   if (fout->remoteVersion >= 90000)
-   {
-       PGresult   *res = ExecuteSqlQueryForSingleRow(fout, "SELECT pg_catalog.pg_is_in_recovery()");
-
-       if (strcmp(PQgetvalue(res, 0, 0), "t") == 0)
-       {
-           /*
-            * On hot standby slaves, never try to dump unlogged table data,
-            * since it will just throw an error.
-            */
-           dopt.no_unlogged_table_data = true;
-       }
-       PQclear(res);
-   }
+   if (fout->isStandby)
+       dopt.no_unlogged_table_data = true;
 
    /* Select the appropriate subquery to convert user IDs to names */
    if (fout->remoteVersion >= 80100)
@@ -1088,7 +1075,16 @@ setup_connection(Archive *AH, const char *dumpencoding,
    else if (AH->numWorkers > 1 &&
             AH->remoteVersion >= 90200 &&
             !dopt->no_synchronized_snapshots)
+   {
+       if (AH->isStandby)
+           exit_horribly(NULL,
+            "Synchronized snapshots are not supported on standby servers.\n"
+                         "Run with --no-synchronized-snapshots instead if you do not need\n"
+                         "synchronized snapshots.\n");
+
+
        AH->sync_snapshot_id = get_synchronized_snapshot(AH);
+   }
 }
 
 static void
@@ -16559,26 +16555,3 @@ fmtReloptionsArray(Archive *fout, PQExpBuffer buffer, const char *reloptions,
    if (options)
        free(options);
 }
-
-/*
- * Execute an SQL query and verify that we got exactly one row back.
- */
-static PGresult *
-ExecuteSqlQueryForSingleRow(Archive *fout, char *query)
-{
-   PGresult   *res;
-   int         ntups;
-
-   res = ExecuteSqlQuery(fout, query, PGRES_TUPLES_OK);
-
-   /* Expecting a single result only */
-   ntups = PQntuples(res);
-   if (ntups != 1)
-       exit_horribly(NULL,
-                     ngettext("query returned %d row instead of one: %s\n",
-                              "query returned %d rows instead of one: %s\n",
-                              ntups),
-                     ntups, query);
-
-   return res;
-}