Neither of them had the structure required for efficient caching,
that is, page/tag retrieval instead of page/revision retrieval. The
basic problem is that tugela, which we are now using instead of
memcached, has no efficient means for identifying and purging
expired keys. In fact at the moment, this garbage collection is not
done at all.
It is actually done. I've purged already tugela caches because of
some weird behavior when more than several gigabytes of cache are
used. I'm wondering whether to return back to memcached or have some
tugela improvements. We do not need gazilibytes of cache at the
moment, and at 27GB or so we already have really high rates of hits.
It could be quite feasible to maintain a time index inside tugela and
use it for some fifo purging. The main important thing now for site
performance is to have good response times in all tiers.
BR,
Domas