I am trying to emulate a pessimistic locking system you would find in an old school database file system, for example cobol. Generally, when a cobol program tries to read a record that is locked by somebody else, the read fails and either a message is displayed by the user or a error handling procedure is executed. I would like to emulate this behavior for legacy code while using mvcc for newer procedures I write.
4 questions: 1. Can you query if a tuple is locked by another transaction (the documentation unclearly suggests this can't be done via the pg_lock view) before executing select for update...? 2. If so, is this reasonable efficient to do, i.e. straight join on oid/xid? 3. If so, is this possible to query without a race condition regarding the lock status? 4. If so, is this likely to be possible in future versions of postgres without non-trivial changes? In other words, if User B attempts to select for update a record that user A has selected for update, it would be nice if User B's query would fail with a NOTICE to act upon. Thanks in advance, Merlin ---------------------------(end of broadcast)--------------------------- TIP 6: Have you searched our list archives? http://archives.postgresql.org