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From Randy Letness <ra...@osafoundation.org>
Subject Re: Concurrent select and insert deadlock on index
Date Thu, 02 Aug 2007 15:00:36 GMT
Bogdan Calmac wrote:
> The attached test is an attempt to simulate a typical data processing
> application, it consists of:
>  - an insert thread that inserts records in batch
>  - a select thread that 'processes' the records inserted by the other
> thread: 'select * from table where id > ?'
>
> The test deadlocks, the trace can be found in 'derby.log' and the java
> stacktraces just before the deadlock in
> 'stacktraces_during_deadlock.txt'.
>
> After examining them, I think that:
>  - the select thread holds an S lock on the root of the PK index: (1,1)
>  - the select thread waits for an S lock on one of the uncommitted inserts
>
>  - the insert thread holds X locks on the inserted records
>  - the insert thread tries to split the btree root of the PK index:
> (1,1) by acquiring an X lock, so it's a deadlock
>
> Before jumping to conclusions, can somebody confirm if this looks like
> an expected behaviour or is it a bug?
>   

This sounds like the same index split deadlock problem I ran into a few 
months ago:

http://mail-archives.apache.org/mod_mbox/db-derby-user/200701.mbox/%3C45C0E3DA.4070903@sbcglobal.net%3E

Unfortunately I wasn't able to find a work around. Increasing the page 
size didn't help.  I think this may be an issue with non MVCC databases.

-Randy



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