It's a pure JavaScript in-memory implementation of some aspects of CouchDB with a nodejs/connect Web front-end.
Wrote this mostly for fun, to understand the inner workings of CouchDB and what it takes to do incremental map/reduce in a language that I actually understand. I've tried to stay true to the core CouchDB API, but having the web layer separate from the inner database means this also becomes an embeddable in-memory CouchDB implementation. Kinda. Sorta.
Dunno at this point. My original thoughts were to build a good-enough in-memory
CouchDB using Node (again in a language that I'm familiar with), especially
the _changes feed for a highly concurrent/async messaging service. Without
any persistence, I'm not sure that this would really work.
Since memcouchd doesn't have any persistence, all the document changes are
not kept around. Because of this, the _changes feed behaves more like redis'
pubsub in that you have to be watching in order to get notified about a change.
The collated sequence (aka the view index) is a simple incrementally sorted
JavaScript array. While this helped me stay sane for the 2-day implementation,
it allowed me to bring up the rest of the system. However, this has huge
scalability issues, because of the excessive use of splice to insert and remove
elements. On my Mac, the map part of the view generation for 100,000 entries
took a couple of seconds. Maybe at some point, I will replace the Store with a
proper 2-3 BTree. Like I said, this was thrown together in a couple of days.
CouchDB uses the ICU collation library and sorts strings in a funky way. While
memcouchd's collation is ordered, strings are sorted using charCode sort
as opposed to the ICU sort. Maybe someone knows of a nodejs ICU wrapper?
I originally wrote the collation in JavaScript for the Interactive CouchDB Tutorial. The
map part is the slowest because of the description above. The reduce in
memcouchd is always re-reduce and currently there's no caching of the
reduced values. But v8 makes this super fast! So maybe there was a point to
this after all.
This was fun and I almost feel like the jRuby guys trying to make things work
like ruby 1.8.6. Except we have the Futon unit tests + CouchOne's awesome
documentation reference, which is a huge time
saver. If you do this, the nodejs/express code will deliver the Futon files
up to the browser so you can run the unit tests against memcouchd. Making
progress on the unit tests pass ratio, though I'm also discovering lots of
little hidden API's that are not completely documented.
ln -s ~/Desktop/CouchDBX.app/Contents/Resources/couchdbx-core/couchdb_1.0.2/share/couchdb/www ./www