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Comment by mooneater | Hacker News Reader

Tip for doing this kind of thing, that works in any language:

In some cases, using more that one type of data structure at the same time will allow you to get the best of both worlds in terms of performance. Ie, a spatial index plus a hash table as an index, over the same data, would allow efficient lookups on spatial predicates as well as attributes, over the same set of nodes.

A simple insight maybe, but not one I discovered without a lot of thought. Typically in university they teach you to use a single data structure type at a time, but really that's like teaching kids the alphabet, without the concept of combining the letters into meaningful words.

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Brilliant, thanks. Yes, RAM is a good option for me.

I figure 2 GB will last me 4 months. Then I can go up to 4, 8, 16, ...

Pretty good.

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.

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).

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

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.

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?

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