On 05/28/2013 07:52 PM, Fabien COELHO wrote:
>
> However I'm not sure that pg_stat_replication currently has the
> necessary information on either side to measure the lag (in time
> transactions, but how do I know when a transaction was committed? or
> number of transactions?).
The BDR codebase now has a handy function to report when a transaction
was committed, pg_get_transaction_committime(xid) .
It also adds pg_xlog_wait_remote_apply and pg_xlog_wait_remote_receive
that can be used with pg_current_xlog_location() to wait until one or
all replicas have caught up, or with LSNs from pg_stat_replication to
(say) wait until all replicas have caught up with the most up-to-date one.
I don't think these depend on anything BDR-specific, though Andres or
Álvaro would be able to say for sure. Take a look in:
git://git.postgresql.org/git/users/andresfreund/postgres.git
on the 'bdr' branch. Be aware that it is rebased regularly, though the
'0.4' tag applied earlier today will remain constant and contains the
functions of interest.
I hope this helps.
-- Craig Ringer http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training & Services
