pg_dump -Fd -j2 on standby in 9.6.6

Hi,

I downloaded the code from this github tag https://github.com/postgres/postgres/archive/REL9_6_8.tar.gz
I unpacked the code on disk where gdb was looking for it /build/postgresql-9.6-9VrjLn/postgresql-9.6-9.6.8

Then I ran this oneliner which is a summary of my debug process. So, apparently pg_dump -Fd -j2 does not work
in the case of pre-9.2 but it also doesn't work for standby servers.

gdb /usr/lib/postgresql/9.6/bin/pg_dump -ex 'set confirm off' -ex 'set listsize 30' -ex 'set pagination off' -ex 'b 1131' -ex 'r -Fd -j2 -d TIMS_SOMEDB -h /var/run/postgresql/pg-prod-7 -f /tmp/TIMS_SOMEDB_fd.dmp' -ex 'l' -ex 'p AH->numWorkers' -ex 'p AH->remoteVersion' -ex 'p dopt->no_synchronized_snapshots' -ex 'q'

1131 else if (AH->numWorkers > 1 &&
1116 * worker, we'll be passed dumpsnapshot == NULL, but AH->sync_snapshot_id
1117 * is already set (if the server can handle it) and we should use that.
1118 */
1119 if (dumpsnapshot)
1120 AH->sync_snapshot_id = pg_strdup(dumpsnapshot);
1121
1122 if (AH->sync_snapshot_id)
1123 {
1124 PQExpBuffer query = createPQExpBuffer();
1125
1126 appendPQExpBuffer(query, "SET TRANSACTION SNAPSHOT ");
1127 appendStringLiteralConn(query, AH->sync_snapshot_id, conn);
1128 ExecuteSqlStatement(AH, query->data);
1129 destroyPQExpBuffer(query);
1130 }
1131 else if (AH->numWorkers > 1 &&
1132 AH->remoteVersion >= 90200 &&
1133 !dopt->no_synchronized_snapshots)
1134 {
1135 if (AH->isStandby)
1136 exit_horribly(NULL,
1137 "Synchronized snapshots are not supported on standby servers.\n"
1138 "Run with --no-synchronized-snapshots instead if you do not need\n"
1139 "synchronized snapshots.\n");
1140
1141
1142 AH->sync_snapshot_id = get_synchronized_snapshot(AH);
1143 }
1144 }
1145
$1 = 2
$2 = 90606
$3 = 0

I was expecting the code to be the same as the one in [1], but it seems to be different (I don't know why)
I wonder why synchronized snapshots are not supported on standby servers. The code in [1] says they should
work for standby servers.

My master is 9.6.6 and my slave is 9.6.6 as well.
Any ideas would be appreciated.

Thank you,
Stefan

[1] https://github.com/postgres/postgres/blob/REL9_6_STABLE/src/bin/pg_dump/pg_dump.c#L689

Stefan Petrea
System Engineer/DBA, Network Engineering

stefan(dot)petrea(at)tangoe(dot)com

tangoe.com

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