> 73,
> Matthew W. Jones (KI4ZIB)
>
http://matburt.net
>
>
> On Wed, Sep 2, 2009 at 3:41 PM, Martin Kersten <
Martin.Kersten@cwi.nl>wrote:
>
> > Matthew Jones wrote:
> > > There's no relational data in these tables, I guess I just need
> > > something internal to manage concurrency... like blocking table locks so
> > > I don't have to wait for a failure in order to manage concurrency on my
> > own.
> > you either have to serialize the updates/access at your client interface,
> > or hook into the MAL kernel to get access to the general lock/semaphore
> > module.
> >
> > >
> > > I noticed in one of my operations which was a single update to a table
> > > that no other processes were using that it gave me that error, informed
> > Optimistic concurrency control should also ensure that non of the
> > concurrent
> > transactions reads stale data.
> > This becomes tricky if you have multiple user sessions with both autocommit
> > and compound transactions, because then the timespans to trigger
> > a transaction failure are larger.
> >
> > > me of the rollback, but the changes still took effect.... which is
> > > alarming since I will now need to:
> > >
> > > 1) Try the operation
> > > 2) If it fails, check to see if the change actually took effect
> > > 3) if the changes didn't take effect re-try the operation
> > >
> > > This is disconcerting.
> > >
> > > 73,
> > > Matthew W. Jones (KI4ZIB)
> > >
http://matburt.net
> > >
> > >
> > > On Wed, Sep 2, 2009 at 3:02 PM, Martin Kersten <
Martin.Kersten@cwi.nl
> > > <mailto:
Martin.Kersten@cwi.nl>> wrote:
> > >
> > > 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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