[storm] Freeze while dropping multiple rows spanning multiple tables

[Stuart Bishop]

akira wrote:
> Hi Gustavo, you are right about the locks, the ere were many locks 
> beeing held. Is there some way I can handle this better?  I´m doomed :-((

Usually this is caused by some other process being badly behaved, and that
is probably the best place to start if it is under your control. Badly
behaved in this case means running for a long time without committing -
maybe it is necessary because there are lot of changes that need to be made
and they need to be done in a single transaction to ensure integrity, or
maybe the developer doesn't fully understand the concept of transactions and
transaction isolation.

If these other processes are legitimately holding locks open for extended
periods of time or you just have to deal with it, then you need to decide
what the correct behaviour should be. You have the choice of blocking,
failing and returning an error, or detecting the outstanding lock and
skipping steps that need that resource.

Blocking is default behaviour in general, and what you probably have now.
There is also a chance, if your process and the competing process are trying
to access resources in different orders, of ending up with a deadlock. Under
PostgreSQL this will raise an exception (what backend are you using?)

If you want either of the other two options or handle deadlocks more
gracefully, it starts getting backend specific. Under PostgreSQL you use the
LOCK statement to explicitly obtain locks on the resources you need. To
detect a competing lock, you start a SAVEPOINT and issue a LOCK TABLE ... NO
WAIT statement which will raise an exception instead of blocking if the lock
cannot be obtained, at which point you can roll back to the savepoint and
continue on or report a pretty error to the user.

(None of this is Storm specific of course).

-- 
Stuart Bishop <stuart at stuartbishop.net>
http://www.stuartbishop.net/

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