On Thu, Sep 8, 2011 at 9:26 AM, Ants Aasma <ants.aa...@eesti.ee> wrote: > When go try to find the new csnmin > and discover that a backend has a csnmin that is too old, we go through > the snapshots of that backend and convert every snapshot under the > desired csnmin to a traditional snapshot.
I thought about something along these lines (though I didn't flesh out the details as much as you have here), but rejected it because the step described above would require all snapshots to be stored in shared memory. That's problematic for several reasons: 1. A backend can have lots of snapshots, potentially requiring an unbounded amount of shared memory. We can't accommodate that. 2. You'd need to protect all of those snapshots with spinlocks or something, which would be wicked expensive, because the owning process would need to take and release that spinlock every time it touched the snapshot. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
