Using memcached with upgraded Subversion FSFS repository

Question

Subversion 1.6 release notes suggest that it's possible to use memcached to "cache data of FSFS repositories". Creating a new repository using svnadmin create has a fsfs.conf file within the db/ subdirectory which contains some examples and documentation for the memcached configuration.

I have two related questions:

1. To enable memcached support, I propose copying a fsfs.conf file from a newly created SVN repository into an existing repository (upgraded to 1.6), and then configuring it - both the upgraded repository and the new one are hosted on an Ubuntu Lucid 64-bit Server Edition. Is it OK/safe to do so?
2. What SVN operations should I expect to be improved (performance-wise) by use of this cache?

Answer 1

I don't see a reason why an upgraded repository would behave differently from a newly created one. They should be functionally equivalent. The settings in fsfs.conf default to disabled, so it should be safe to copy it from a new repo. However, if you're in doubt I'd suggest copying the repo, enabling the memcached support, and running some test operations on the copy.

As far as I can tell from comments on the web, the cache helps reduce the amount of I/O, so will help most if you're quite I/O limited. People with fast disks or a SAN have reported very little benefit. Can't find many reports on performance though. You should do your own tests to see if it will benefit you.