Re: When the Session ends in PGSQL?

On 4/07/2011 7:50 PM, Durumdara wrote:

> As I understand you then running Queries forced to abort on the end of
> Session and no more Query running over the session's ending point (or
> after TCP connection broken).

Correct. The server might not notice that the client broke it's
connection for a while, though, especially if there's along tcp timeout,
no keepalives are enabled, and the server isn't actively sending data to
the client.

This makes me wonder, though: If a client sends a COMMIT message to the
server, and the server replies to the client to confirm the commit but
the client has vanished, is the data committed? How does the client find
out? I'd assume it'd still be committed, because if the server had to
wait for the client to acknowledge there would be issues with delaying
other commits. The trouble is, though, that if a client sends a COMMIT
then loses contact with the server it doesn't know for sure if the
commit really happened. It can't reconnect to its old session as it's
been destroyed. Is there any way it can ask the server "did my old xid
commit successfully' if it recorded the xid of the transaction it lost
contact with during COMMIT?

Is there any way to have both server and client always know, for
certain, whether a commit has occurred without using 2PC?

>> Stored procedures will remain. Note that "stored procedures" in postgres are a
>> bit different from what you may be used to in other dbs; while I assure you
>> it's for the better, you might want to RTFM to avoid surprises.
>
> Please explain a little this (Just 1-2 sentence please).

PostgreSQL doesn't have true stored procedures at all. It only has
user-defined functions that can be called from a
SELECT/INSERT/UPDATE/DELETE statement.

Most importantly, PostgreSQL's "stored procedures" cannot control
transactions. They cannot commit, rollback, or begin a new transaction.
They have some control over subtransactions using PL/PgSQL exceptions,
but that's about it.

--
Craig Ringer