zc.lockfile.LockError in ZODB

Question

I am trying to use ZODB 3.10.2 on my web server which is running Debian and Python 2.7.1. It seems like every time I try to access the same database from 2 different process

Answer 1

You can not access the same database files from two processes at the same time (which is obvious). That's why you get this error. If you need to perform actions on the same data.fs file from two or more processes: use ZEO.

Answer 2

The ZODB does not support multi-process access. This is why you get the lock error; the ZODB file storage has been locked by one process to prevent other processes altering it.

There are several ways around this. The easiest option is to use ZEO. ZEO extends the ZODB machinery to provide access to objects over a network, and you can easily configure your ZODB to access a ZEO server instead of a local FileStorage file:

<zodb>
    <zeoclient>
    server localhost:9100
    </zeoclient>
</zodb>

Another option is to use RelStorage, which stores the ZODB data in a relational database. RelStorage supports PostgreSQL, Oracle and MySQL backends. RelStorage takes care of concurrent access from different ZODB clients. Here is an example configuration:

<zodb>
  <relstorage>
    <postgresql>
      # The dsn is optional, as are each of the parameters in the dsn.
      dsn dbname='zodb' user='username' host='localhost' password='pass'
    </postgresql>
  </relstorage>
</zodb>

RelStorage requires more up-front setup work but can outperform ZEO in many scenarios.