Re: advancing snapshot's xmin

On Tue, 2008-03-25 at 17:26 -0300, Alvaro Herrera wrote:
> There is one hole here: contention on ProcArrayLock.  Basically, for
> simple transactions we will need to update MyProc after every command.

If we're just updating MyProc->xmin, we only need to acquire
ProcArrayLock in shared mode, right?

> Another idea is to throttle the updating of Xmin so it only happens once
> in a while, but it's difficult to find a useful criterion and avoid
> falling into the trap that we just neglected to update it before a large
> command.

Using LWLockConditionalAcquire() might help also.

-Neil