Re: Can pessimistic locking be emulated?

>
> 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.
>
No idea if this is of any help, but you may have a look into
PostgreSQL 7.3 Documentation
3.4. Run-time Configuration
STATEMENT_TIMEOUT (integer)
Aborts any statement that takes over the specified number of
milliseconds. A value of zero turns off the timer.

Regards, Christoph