On Tue, Nov 22, 2011 at 7:25 PM, Simon Riggs <si...@2ndquadrant.com> wrote: > On Tue, Nov 22, 2011 at 11:40 PM, Simon Riggs <si...@2ndquadrant.com> wrote: >>> I think this is unsafe for shared catalogs. >> I think so too. Thats why it uses IsMVCCSnapshot() to confirm when it >> is safe to do so. > Ah, you mean access to shared catalogs using MVCC snapshots.
Yeah. This change would have the disadvantage of disabling HOT cleanup for shared catalogs; I'm not sure whether that's a good decision. But now that you mention it, something seems funky about the other bit you mention, too: + /* MVCC snapshots ignore other databases */ + if (!allDbs && + proc->databaseId != MyDatabaseId && + proc->databaseId != 0) /* always include WalSender */ + continue; + It doesn't make sense for the RecentGlobalXmin calculation to depend on whether or not the current snapshot is an MVCC snapshot, because RecentGlobalXmin is a global variable not related to any particular snapshot. I don't believe it's safe to assume that RecentGlobalXmin will only ever be used in conjunction with the most-recently-taken 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
