choosing the right locking mode

[rihad <rihad@xxxxxxx>]

Given this type query:

        UPDATE bw_pool
        SET user_id=?
        WHERE bw_id=
                (SELECT MIN(bw_id) FROM bw_pool WHERE user_id IS NULL)
        RETURNING bw_id

The idea is to "single-threadedly" get at the next available empty slot, 
no matter how many such queries run in parallel. So far I've been 
semi-successfully using LOCK TABLE bw_pool before the UPDATE, but it 
deadlocks sometimes. Maybe I could use some less restrictive locking 
mode and prevent possible collisions at the same time?

Thanks.

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