MemoryMappedFile and b-tree for cache application

Question

This is just an idea, I don't yet have any code, I need some design advice. I would implement a cache ( non distributed in first instance ) by using the MemoryMappedFile in c#. I think it would be good to have a b-tree as an undelying structure, but this is debatable as well. So the question are:

Is B-tree a good strategy to use to fast search items when the undelaying support is a memory mapped files ?
What tip and trick do we have with memory mapped files ? How much the view can be large, what are the drawbacks when it is too small or too large ?
Multithread consideration: how we deal with memory mapped file and concurrency ? Cache are supposed to be higly hitten by clients, what strategy is better to have something performant ?

As @Internal Server Error asked, I integrate the question with this: Key would be a string, about 64 chars max len. The data would be a byte[] about 1024 bytes long but consider an average at 128 bytes, or better: what I want to cache are OR/M entities, let's consider how long is a serialized entity in bytes with something like a BSOn serializer.

What is the data type(s) you are caching? What type is the key? How much data are we talking about? — 500 - Internal Server Error, Oct 27 '11 at 20:26
key will be a string, consider something about 64 chars. Data vould be an array of bytes: a serialized entity, something from 4 to 1k byte probably. — Felice Pollano, Oct 27 '11 at 20:29
why roll your own? couchdb, memcached, mongodb; apparently mongodb is _fast_ — sehe, Oct 27 '11 at 21:46
@sehe you are right, I know mongodb, but I want something embeddable in my project — Felice Pollano, Oct 28 '11 at 05:03

score 1 · Accepted Answer · edited May 23 '17 at 11:56

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B-Tree is good (with memory-mapped files), but if the file is not always entirely kept in resident memory then a page-aligned B+Tree is much better. See also.
The trick with memory-mapped files is to use a 64-bit architecture so that you can map the entire file into memory, otherwise you'd have to only map the parts and the cached reads might be faster than mmaps.
Try CAS (compare-and-swap) over the shared memory. See also.

edited May 23 '17 at 11:56

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answered Oct 05 '12 at 17:44

ArtemGr

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Maybe there is something C#-pish for you at [nosql-database.org](http://nosql-database.org/). Or [some C project](http://highlandsun.com/hyc/mdb/) might serve as a reference. – ArtemGr Oct 21 '12 at 14:23

MemoryMappedFile and b-tree for cache application

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