2009/9/14 Geir Bækholt · Jarn <
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>
> On 10. sep.. 2009, at 00.26, Darryl Dixon - Winterhouse Consulting wrote:
>
>> I'm very interested in this. We have a major client with an existing
>> Oracle RAC infrastructure that could be utilised for this. What sorts of
>> caveats are there around using loadbalanced/failover connections to the
>> RAC instance from Zope? Are there any limitations on replacing FileStorage
>> with RelStorage, or situations where it would be contra-indicated?
>
> If you already have an Oracle cluster, there isn't much overhead. For
> write-intensive applications you should see a performance increase. Each ZEO
> client has its own connection directly to the RAC, so there is no need for
> extra loadbalancing beyond the one in front of the ZEO clients.
>
> It would be contra-indicated in all situations where you don't need the
> enterprise-ness of the Oracle Cluster and don't have the RAC running
> already. Filestorage is wonderful for its simplicity and flxibility in
> dealing with backups and moving servers etc as long as your demands are
> within its scope.
To clarify a little, in our experience the network latency between the
Application Server and Database machines has a large effect on
performance, which is particularly acute before the object cache is
filled (as serial object loads multiply the network latency). Oracle
RAC also suffers from additional write latency inherent in any
multi-master transactional system:
"In RAC the node performing the write-transaction must take
ownership of the relevant area of the database: typically this
involves a request across the cluster interconnection (local IP
network) to transfer the data-block ownership from another node to the
one wishing to do the write. This takes a relatively long time (from
few milliseconds to tens of milliseconds) compared to single
database-node using in-memory operations."
http://en.wikipedia.org/wiki/Oracle_RACGiven this, I would be reluctant to recommend such a system unless you
have a corporate data-management policy mandating it, or a very strict
availability requirement. For pure performance, it is difficult to
beat a single multi-core system packed with memory and fast disks. But
then you have to deal with failover yourself.
Laurence
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