Neil Conway <[EMAIL PROTECTED]> writes: > The decision to store prepared statements per-backend, rather than in > shared memory, was made deliberately. In fact, an early version of the > PREPARE/EXECUTE patch (written by Karel Zak) stored prepared statements > in shared memory. But I decided to remove this, because: > [ several good reasons ]
Another issue is that we currently don't have a mechanism for flushing query plans when they become obsolete (eg, an index is added or removed). Locally-cached plans are relatively easy to refresh: just start a fresh session. A shared plan cache would retain bogus plans forever, short of a postmaster restart. Obviously we need a mechanism for detecting and handling cached-plan invalidations, and I hope someone will get around to that soon. But we *cannot* consider a shared plan cache until that mechanism exists. If I recall correctly, Karel's original shared plan cache also triggered a lot of concern about contention for the shared data structure ... I'm not convinced that it would be a big bottleneck, but there's definitely an issue to think about there ... regards, tom lane ---------------------------(end of broadcast)--------------------------- TIP 9: the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match