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From Bryan Pendleton <bpendle...@amberpoint.com>
Subject Re: disabling locking
Date Tue, 31 Mar 2009 14:50:23 GMT
> As another data-point, if I create an index for the 'version' column
> then it doesn't hang (at least not in this example):

Indeed, careful design and use of indexes is crucial to avoiding
concurrency problems such as these, as well as for achieving
satisfactory performance on queries.

It's a little surprising that you are having trouble getting Derby
to use the index. This may be an artifact of having very small tables
and/or out-of-date statistics, as these situations can cause Derby
to make unexpected query plan choices.

You can read more about query plan selection, index usage, and
table statistics in the Derby documentation.

Your observation that it's not possible to use optimizer overrides
(the --DERBY_PROPERTIES special comment) for searched UPDATE and
DELETE statements is interesting; I wasn't aware that we had that
restriction. This sounds like a useful enhancement request.

It's good to hear that you are having better success now that you
have indexes in place. Hopefully you will be able to get the
performance and concurrency you need once you get more experience
using the indexes.



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