At 09:39 AM 20-08-2001 -0700, Mikheev, Vadim wrote:
>> If it does then one of the things I'd use it for is to insert
>> unique data without having to lock the table or rollback on
>> failed insert (unique index still kept as a guarantee).
>
>(Classic example how could be used SAVEPOINTs -:))
I guess so. But this could be faster.
>So, in your application you would first lock a key in excl mode
>(for duration of transaction), than try to select and insert unless
>found? (Note that this will not work with serializable isolevel.)
yep:
lock "tablename.colname.val=1"
select count(*) from tablename where colname=1
If no rows, insert, else update.
(dunno if the locks would scale to a scenario with hundreds of concurrent
inserts - how many user locks max?).
Why wouldn't it work with serializable isolevel?
Anyway, I believe that isolevel doesn't really serialise things in this
case (inserting a unique row) so it wouldn't matter to me.
Regards,
Link.
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