> > OTOH DB2 and SQLServer take block level > > read locks, so they can do this too, but at major loss of concurrency > > and threat of deadlock.
Note, that in the usual committed read isolation, they do not need to read lock a row ! e.g. Informix only verifies, that it could lock the row (that there is no write lock). Only cursor stability leaves one read lock until the next fetch, serializable actually leaves all read locks, and select for update an intent update lock. Also they usually feed a buffer of rows to the client, so if the client does a fetch it gets a row from the client side buffer. Only when the buffer is empty, they get more from the server. I think the statement holds, that the optimization is pg specific, and cannot be directly compared to other db's. Andreas ---------------------------(end of broadcast)--------------------------- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly