master-side counterpart of pg_last_xact_replay_timestamp?

[Chris Redekop <chris@xxxxxxxxxxxx>]

Is there anything available to get the last time a transaction occurred?....like say "pg_last_xact_timestamp"?  In order to accurately calculate how far behind my slave is I need to do something like master::pg_last_xact_timestamp() - slave::pg_last_xact_replay_timestamp()....currently I'm using now() instead of the pg_last_xact_timestamp() call, but then when the master is not busy the slave appears to lag behind.  I'm considering writing a C module to get the last modified file time of the xlog, but I'm hoping there is a better alternative that I haven't found yet....