Dear Matthew,
A quick initial reaction. MonetDB uses an optimistic concurrency control
scheme, which is geared at high-read, low-write applications. If you hit
the system with multiple concurrent writes on the same table, then indeed
to secure acid properties, transactions are bound to fail. MonetDB indeed
conforms to the semantics of a transaction safe system.
Blocking queries is equivalent to relation level locking.
This is not the preferred way to go for the kernel, because someone
will immediately ask for more granularities and als relaxation of
the ACID principles.
There are several application scenarios to deal with this issue,
but all depend on the semantics required.
regards, Martin
> ------------------------------------------------------------------------
Matthew Jones wrote:
> I have multiple processes reading and writing to the same table and I've
> noticed really persistent concurrency problems:
>
> File "/usr/lib/python2.5/site-packages/monetdb/sql/cursors.py", line
> 208, in execute
> self.__store_result(block)
> File "/usr/lib/python2.5/site-packages/monetdb/sql/cursors.py", line
> 520, in __store_result
> self.__exception_handler(InterfaceError, "Unknown state, %s" % block)
> File "/usr/lib/python2.5/site-packages/monetdb/sql/cursors.py", line
> 574, in __exception_handler
> raise exception_class(message)
> InterfaceError: Unknown state, &2 65541 -1
> !ERROR: COMMIT: transaction is aborted because of concurency conflicts,
> will ROLLBACK instead
>
> I'm not sure what the problem is, but it exists in such a way that all
> operations that load or update information in MonetDB have to be put
> into a loop to continuously retry.
>
> I'm using autocommit, but I would expect MonetDB to handle concurrency
> issues in a decent way, like maybe blocking a query until the other
> query finished. I'm not clobbering data, most of these are just bulk
> load operations that insert new rows.
>
> Is there any way to address this issue without having to putting retry
> loops around all of the code I'm writing to write to the database?
>
> 73,
> Matthew W. Jones (KI4ZIB)
> http://matburt.net
>
>
>
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