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.pet...@tangoe.com 

         

tangoe.com



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