Re: [Tm4j-developers] database deadlocks

[Kal A. <ka...@te...>]

Hi Pete,

Did you make these changes to the schema generated by Hibernate or did
you change the Hibernate mapping files ? If you did the latter, would it
be possible to get a copy of your changes ? If you had to hack the
schema generated by Hibernate then I'm a little less clear on the best
way to proceed - on the one hand this is an issue we should try to
address, but on the other hand I don't want to have to create and
maintain a set of schemas for different databases (that was one of the
reasons for using Hibernate in the first place!) - perhaps it could be
reported as an issue to the Hibernate folks though ?

Cheers,

Kal

On Fri, 2004-08-06 at 10:35, Pete Lewin-Harris wrote:
> I'm getting a problem with deadlocks being reported by the database when I
> load test tm4j using multiple threads adding, editing and deleting topics on
> multiple topic maps. I'm running with the hibernate backend and a postgres
> database.
> 
> I've googled this problem and it seems that it is a known postgres
> 'feature'. The point is that before updating a row the database locks for
> update all foreign keys for that row. This can cause problems if there are
> many foreign keys on a table (such as tmobjects in tm4j) due to different
> threads trying to lock the same table rows in different orders (i.e. an add
> locks rows in a different order to an edit) and so deadlocks can appear.
> 
> The soultion to this seems to be changing the schema to reduce the
> likelyhood of deadlocks. I have managed to reduce the frequency of this
> problem by reordering the foreign keys and removing the foriegn key from the
> topicMap column on tmobjects to topicmaps but this is a fairly temporary
> bodge.
> 
> cheers, Pete
> 
> 
> 
> 
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-- 
Kal Ahmed <ka...@te...>
techquila