[Zope-dev] HA storage for zope

[Hanno Schlichting]

Wichert Akkerman wrote:
> Previously Miles Waller wrote:
>> 1. RelStorage
>> Using this, I think I can then take care of replication/mirroring as I have
>> access to a database that is already clustered in a HA environment.  My
>> questions are:
>>  + Are the connections opened only when zope is started?  Say I unplugged a
>> network cable and then plugged it back in again (breaking the database
>> connection) - will it be re-opened?

Connections will be re-opened should they be lost for any reason. I
remember only one instance of non-recoverable connection loss in an
entire year now. This was caused by maintenance tasks on the Oracle
cluster. The changes in 1.1.3 might have fixed even this rare problem.

>>  + How does RelStorage take care of the blob storage?

RelStorage has no special blob storage support. You can wrap a
file-system based blob storage around a RelStorage. We don't use blobs
for this project at Jarn but store all information directly in Oracle.
Depending on the kind of data you need to store this can be inefficient.

>>  + Are there any details of big sites out there that use RelStorage
>> (particularly on Oracle)?
> 
> The initial RelStorage development was sponsored by Jarn and Elkjøp for
> exactly that purpose: Elkjøp (a chain of Scandinavian electronics
> stores) uses an Oracle cluster for storage of all their Zope data.

Exported to a regular Data.fs the data size is about 20gb. We have 20
Zope clients connected to the storage in the setup.

The only problem we found with this setup is that the Oracle Cluster has
quite a high latency, so reading and writing lots of objects to the
database can be slow. We aren't using the "cache-servers" option yet,
which should help with this specific problem.

One additional advice: You want to increase your temporary table space
to a much larger value. If you pack the database, the tempspace should
be able to contain your entire data set.

If you decide for RelStorage, Shane offers commercial support and
consultancy for it, which might be worth considering depending on the
criticality of the application.

Hanno