How to store a multimap?

[JamesHinshelwood]

Hi, thanks for the cool library :)

I'm currently evaluating redb and fjall. One of the features we use in redb is multimap tables which allow you to store a list of values with each key.

At a first glance, I don't see an equivalent in fjall. Are there any plans to implement this or other ways we could store the data that would fit with fjall's model?

[marvin-j97]

It definitely depends on your data.

Naively, you could just encode your array into a single KV, and update that using update_fetch.

Alternatively, you could use a common prefix:

key1#value1
key1#value2
key1#value3

This probably is the way to go if there can be many values, and/or you want to only update, delete or scan some of the values.

For example, a secondary index in a RDBMS is logically a multi map (indexed column -> Rows), and is implemented using such common prefix.

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To me, a MultiMap API kind of hides of what's actually going on at the storage level (I'm guessing redb uses something like the 1st approach), so I don't think it's really necessary.