Re: advance local xmin more aggressively

Jeff Davis <pgsql@j-davis.com> writes:
> With the new snapshot maintenance code, it looks like we can advance the
> xmin more aggressively.

The original design for that contemplated having snapmgr.c track
all the snapshots (cf the comment for RegisteredSnapshots).  I don't
particularly care for having it assume that it can find all the resource
owners.

But really the more important problem is to demonstrate that you
actually get a benefit commensurate with the additional cycles spent.
IIRC the reason the code is the way it is is that we concluded that for
typical usage patterns there wouldn't be any win from tracking things
more aggressively.  As somebody pointed out recently, SnapshotResetXmin
is called quite a lot; if it's expensive it's going to be a problem.
        regards, tom lane