(2012/04/08 5:19), Thom Brown wrote: > 2012/4/7 Shigeru HANADA<shigeru.han...@gmail.com>: >> I've updated pgsql_fdw so that it can collect statistics from foreign >> data with new FDW API. > > I notice that if you restart the remote server, the connection is > broken, but the client doesn't notice this until it goes to fire off > another command. Should there be an option to automatically > re-establish the connection upon noticing the connection has dropped, > and issue a NOTICE that it had done so?
Hm, I'd prefer reporting the connection failure and aborting the local transaction, because reconnecting to the server would break consistency between the results come from multiple foreign tables. Server shutdown (or other troubles e.g. network failure) might happen at various timing in the sequence of remote query (or sampling in ANALYZE). For example, when we execute a local query which contains two foreign tables, foo and bar, then the sequence of libpq activity would be like this. 1) connect to the server at the beginning of the local query 2) execute EXPLAIN for foreign table foo 3) execute EXPLAIN for foreign table bar 4) execute actual query for foreign table foo 5) execute actual query for foreign table bar 6) disconnect from the server at the end of the local query If the connection has broken between 4) and 5), and immediate reconnect succeeded, retrieved results for foo and bar might be inconsistent from the viewpoint of transaction isolation. In current implementation, next local query which contains foreign table of failed foreign table tries to reconnect to the server. > Also I'm not particularly keen on the message provided to the user in > this event: > > ERROR: could not execute EXPLAIN for cost estimation > DETAIL: FATAL: terminating connection due to administrator command > FATAL: terminating connection due to administrator command > > There's no explanation what the "administrator" command was, and I > suspect this is really just a "I don't know what's happened here" > condition. I don't think we should reach that point. That FATAL message is returned by remote backend's ProcessInterrupts() during some administrator commands, such as immediate shutdown or pg_terminate_backend(). If remote backend died of fast shutdown or SIGKILL, no error message is available (see the sample below). postgres=# select * From pgsql_branches ; ERROR: could not execute EXPLAIN for cost estimation DETAIL: HINT: SELECT bid, bbalance, filler FROM public.pgbench_branches I agree that the message is confusing. How about showing message like "pgsql_fdw connection failure on <servername>" or something with remote error message for such cases? It can be achieved by adding extra check for connection status right after PQexec()/PQexecParams(). Although some word polishing would be required :) postgres=# select * from pgsql_branches ; ERROR: pgsql_fdw connection failure on subaru_pgbench DETAIL: FATAL: terminating connection due to administrator command FATAL: terminating connection due to administrator command This seems to impress users that remote side has some trouble. Regards, -- Shigeru HANADA -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers