Zeugswetter Andreas ADI SD wrote: > > > > Is there a particular reason why CLUSTER isn't MVCC-safe? It seems > to > > > me that it would be trivial to fix, by using SnapshotAny instead of > > > SnapshotNow, and not overwriting the xmin/xmax with the xid of the > > > cluster command. > > > > It's trivial to fix now in this way, but it would break HOT, > > since an indexscan only returns one row per index entry. > > Well, with SnapshotAny HOT should probably return all possibly visible > tuples > with an indexscan. (Btw, does CLUSTER really do an index scan ? Seems > for reading a whole table a seq scan and sort is usually cheaper, at > least when the clustering is so bad that a CLUSTER is needed.)
Yes, it does an indexscan (last time I checked, at least). I think if a performance improvement is demonstrated, we would accept a patch ... -- Alvaro Herrera http://www.CommandPrompt.com/ PostgreSQL Replication, Consulting, Custom Development, 24x7 support ---------------------------(end of broadcast)--------------------------- TIP 7: You can help support the PostgreSQL project by donating at http://www.postgresql.org/about/donate
