[robmnl]

mooneater, do you have any suggestions on how to actually store and persist such a data structure in RAM?

Would I use something like a wsgi webserver, that runs as a daemon, and occasionally dumps the data structure to disk?

Or is something like memcached better?

My preferred way of storing into RAM would be of course only storing changes, instead of storing the whole tree into RAM on every write.

[mooneater]

Depends how often you are getting new data. If its not too often, you could write directly to SQL. Otherwise writing in batches like you suggest could work too.

After looking at your post again, and depending on data volume, you might be ok with a purely SQL solution too (ie, finding nodes 1 or 2 steps away on a graph is easy in SQL if your adjacency data is all in the db).

[robmnl]

Yes, that's true. But I still have a requirement for a schemaless db, so sql doesn't cut it.

[bayareaguy]

By schema-less, do you mean that it's possible that every new record in the database could have a few attribute-values that no other record has, or that you simply don't know what your attributes are at this time but at some point you will know them all?

[mooneater]

If by schemaless you mean the arbitrary name/attribute pairs, you could simply use SQL, with an "attribute" table with "name" and "value", and "nodeid" columns.