On Wed, 2003-10-01 at 20:25, Jingren Zhou wrote: > From the document, it seems that PREPARE/EXECUTE works only in the same > session. I am wondering whether postgres can prepare a query (save the plan) > for difference backends.
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: - it is more complex - since shared memory must be allocated statically on postmaster startup, it would make prepared statements more fragile: at some point we would run out of room in shm, and need to either remove prepared statements, or swap them out to disk - it would encourage poor application design, since it wouldn't be trivial to tell whether a given prepared query has already been prepared by a different backend, and what name it is using - the performance gains are not that dramatic: preparing a statement once per active backend is not that expensive. In most of the cases where prepared statements are useful, since the # of backends is usually far smaller than the # of times you're executing a given prepared statement That's all the reasons I can think of off the top of my head for doing things the way we do. However, I'm open to being convinced: if you think we should store prepared statements in shm, feel free to make a case for it. -Neil ---------------------------(end of broadcast)--------------------------- TIP 1: subscribe and unsubscribe commands go to [EMAIL PROTECTED]