TCP keepalive support for libpq
in [PgSql]
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From: Magnus Hagander on 11 Feb 2010 04:18 2010/2/10 daveg <daveg(a)sonic.net>: > On Tue, Feb 09, 2010 at 09:34:10AM -0500, Andrew Chernow wrote: >> Tollef Fog Heen wrote: >> >(please Cc me on replies, I am not subscribed) >> > >> >Hi, >> > >> >libpq currently does not use TCP keepalives. This is a problem in our >> >case where we have some clients waiting for notifies and then the >> >connection is dropped on the server side. The client never gets the FIN >> >and thinks the connection is up. The attached patch unconditionally >> >adds keepalives. I chose unconditionally as this is what the server >> >does. We didn't need the ability to tune the timeouts, but that could >> >be added with reasonable ease. >> >> ISTM that the default behavior should be keep alives disabled, as it is >> now, and those wanting it can just set it in their apps: >> >> setsockopt(PQsocket(conn), SOL_SOCKET, SO_KEEPALIVE, ...) > > I disagree. I have clients who have problems with leftover client connections > due to server host failures. They do not write apps in C. For a non-default > change to be effective we would need to have all the client drivers, eg JDBC, > psycopg, DBD-DBI, and the apps like psql make changes to turn it on. Adding > this option as a non-default will not really help. Yes, that's definitely the use-case. PQsocket() will work fine for C apps only. But it should work fine as an option, no? As long as you can specify it on the connection string - I don't think there are any interfaces that won't take a connection string? -- Magnus Hagander Me: http://www.hagander.net/ Work: http://www.redpill-linpro.com/ -- Sent via pgsql-hackers mailing list (pgsql-hackers(a)postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
From: Fujii Masao on 11 Feb 2010 21:52 On Fri, Feb 12, 2010 at 1:33 AM, Peter Geoghegan <peter.geoghegan86(a)gmail.com> wrote: > Why hasn't libpq had keepalives for years? I guess that it's because keepalive doesn't work as expected in some cases. For example, if the network outage happens before a client sends some packets, keepalive doesn't work, then it would have to wait for a long time until it detects the outage. This is the specification of linux kernel. So a client should not have excessive expectations of keepalive, and should have another timeout like QueryTimeout of JDBC. Regards, -- Fujii Masao NIPPON TELEGRAPH AND TELEPHONE CORPORATION NTT Open Source Software Center -- Sent via pgsql-hackers mailing list (pgsql-hackers(a)postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
From: Andrew Chernow on 11 Feb 2010 08:44 >>> ISTM that the default behavior should be keep alives disabled, as it is >>> now, and those wanting it can just set it in their apps: >>> >>> setsockopt(PQsocket(conn), SOL_SOCKET, SO_KEEPALIVE, ...) >> I disagree. I have clients who have problems with leftover client connections >> due to server host failures. They do not write apps in C. For a non-default >> change to be effective we would need to have all the client drivers, eg JDBC, >> psycopg, DBD-DBI, and the apps like psql make changes to turn it on. Adding >> this option as a non-default will not really help. > > Yes, that's definitely the use-case. PQsocket() will work fine for C apps only. > > But it should work fine as an option, no? As long as you can specify > it on the connection string - I don't think there are any interfaces > that won't take a connection string? > Perl and python appear to have the same abilities as C. I don't use either of these drivers but I *think* the below would work: DBD:DBI setsockopt($dbh->pg_socket(), ...); psycopg conn.cursor().socket().setsockopt(...); Although, I think Dave's comments have made me change my mind about this patch. Looks like it serves a good purpose. That said, there is no guarentee the driver will implement the new feature ... JDBC seems to lack the ability to get the backing Socket object but java can set socket options. Maybe a JDBC kong fu master knows how to do this. -- Andrew Chernow eSilo, LLC every bit counts http://www.esilo.com/ -- Sent via pgsql-hackers mailing list (pgsql-hackers(a)postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
From: Robert Haas on 11 Feb 2010 11:16 On Thu, Feb 11, 2010 at 2:15 AM, Tollef Fog Heen <tollef.fog.heen(a)collabora.co.uk> wrote: > ]] daveg > > | I disagree. I have clients who have problems with leftover client connections > | due to server host failures. They do not write apps in C. For a non-default > | change to be effective we would need to have all the client drivers, eg JDBC, > | psycopg, DBD-DBI, and the apps like psql make changes to turn it on. Adding > | this option as a non-default will not really help. > > FWIW, this is my case. My application uses psycopg, which provides no > way to get access to the underlying socket. Sure, I could hack my way > around this, but from the application writer's point of view, I have a > connection that I expect to stay around and be reliable. Whether that > connection is over a UNIX socket, a TCP socket or something else is > something I would rather not have to worry about; it feels very much > like an abstraction violation. I've sometimes wondered why keepalives aren't the default for all TCP connections. They seem like they're usually a Good Thing (TM), but I wonder if we can think of any situations where someone might not want them? ....Robert -- Sent via pgsql-hackers mailing list (pgsql-hackers(a)postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
From: "Kevin Grittner" on 11 Feb 2010 11:27
Robert Haas <robertmhaas(a)gmail.com> wrote: > I've sometimes wondered why keepalives aren't the default for all > TCP connections. They seem like they're usually a Good Thing > (TM), but I wonder if we can think of any situations where someone > might not want them? I think it's insane not to use them at all, but there are valid use cases for different timings. Personally, I'd be happy to see a default of sending them if a connection is idle for two minutes, but those people who create 2000 lightly used connections to the database might feel differently. -Kevin -- Sent via pgsql-hackers mailing list (pgsql-hackers(a)postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers |