I've researched the recent discussions about statement_timeout
and NOWAIT and I'd like to confirm my understanding of the
situation before acting on it. Please let me know if the
following statements are true:
- LOCK TABLE ... NOWAIT has been checked in and will be available
in 7.5
- SELECT ... FOR UPDATE NOWAIT is in the TODO list (among other
NOWAIT commands) but it will also be available in 7.5
- Using "SET LOCAL statement_timeout=xxx" can be used before
"SELECT ... FOR UPDATE" to emulate NOWAIT when the select
is simple and involves a relatively small number of rows.
That is, the following:
BEGIN;
SET LOCAL statement_timeout=3000;
SELECT ... FOR UPDATE; -- (1 row)
COMMIT;
will be equivalent to:
BEGIN;
SELECT ... FOR UPDATE NOWAIT;
COMMIT;
- The NOWAIT feature will be able to handle select-for-updates
that involve many rows better than statement_timeout because
it will track timeouts on a row by row basis, which eliminates
false positives. That is, if the statement_timeout is too
short for the select, it might fail before finishing the select
instead of failing because of locked row.
- The error raised by statement_timeout and NOWAIT will be the
same.
Basically, I'd like to write low level code that implements
NOWAIT in the application using statement_timeout. Later on,
7.5, I'd be able to reimplement the low level functions using
NOWAIT without having to change the higher level code.
Your thoughts and comments are appreciated.
Thanks
Luis P Caamano
Atlanta, GA, USA
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