On Fri, 2011-02-18 at 11:44 +0900, Fujii Masao wrote: > > This begs the questions "what is the xmin of all the normal > backends?" > > and "Whats is the xmin of prepared transactions?" as well. I wasn't > sure > that we should expose that information for walsenders when we > don't do > it for everybody else. If we do it would require major > sections in the > docs explaining it all, etc.. > > We can *presume* which backend (or prepared transaction) unexpectedly > prevents VACUUM by seeing pg_stat_activity (or pg_prepared_xacts) and > checking whether there is long-running transaction. But there is no > way to presume which standby does that, I'm concerned.
Currently there is no information available to users about xmin. It isn't any *harder* to work out standby xmins than it is to work out prepared transaction xmins or other backend xmins. For example, we don't show which transactions use serializable mode on pg_stat_activity and so we might make the mistake of reading the last statement start time rather than the last transaction start time. I see it as a major piece of work to add xmin in *all* the right places and to fully document how to use that information as a user. The debug information at DEBUG2 is sufficient to show the code works and to debug issues if needed. I agree with you that it would be nice to have a "which thing is bloating my tables" device, but I'm not assuming the responsibility to create such a thing and fully document it, and definitely not Right Now. -- Simon Riggs http://www.2ndQuadrant.com/books/ PostgreSQL Development, 24x7 Support, Training and Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
