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I'm going to start my Master of Science degree work. My goal is to implement (and test in various scenarios) hybrid database environment: my application will communicate with two databases. One will be in-memory database and other will be standard (on hard disk) database. I want to research if this hybrid can be faster than standard database only (in certain situations).

Have you ever heard or read of someone, who tried something like this? Because if there are works like that I would like compare my results to them.

I'm on beginning of my work, so exact topic is not cleared yet (I have something about 18 months to write it).
My main idea is to compare standard database (eg MySQL) vs hybrid (eg MySQL+VoltDB) with the same set of data, where on hybrid some tables (or maybe some columns from some tables) will be in in-memory database.
Mainly I want to compare time performance, but maybe other aspects (like administration issues of that hybrid) as well.

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Which aspects are you comparing? Are you comparing a single database to two databases using multi-master replication or a single database to two databases each handling a subset of the data? If the later is the client software handling the query complexity or are all queries sent to one of the databases which uses views with database links to retrieve data from the other database for join operations. – Leigh Riffel Dec 6 '12 at 13:49
Or are you perhaps comparing two traditional databases on one computer with two databases on another computer with one of them being in-memory? Are you allowing "disk only" database access to the equivalent resources as the other system in terms of the number of nodes, and amount of memory? – Leigh Riffel Dec 6 '12 at 13:50
There are many more questions I could ask and you've probably considered most of them, so perhaps you could edit your answer to clarify what you are doing. – Leigh Riffel Dec 6 '12 at 13:50
You might also want to consider traditional spindles vs. SSD storage (vs. RAM). There are some emerging SSD options which have very high read/write speeds - many times higher than "older" SSD and 7,200rpm technologies. – Joel Brown Dec 6 '12 at 20:51
@JoelBrown - This could be interesting research, but on my faculty there is no machine with SSD storage, so I have no environment to perform such tests. – Michał Herman Dec 7 '12 at 7:37

Microsoft just announced Hekaton which allows you to have a mix of in-memory tables and traditional on-disk tables in the same database, and seemlessly integrate the two technologies. It will ship in the next major release. They annouced it at the 2012 SQLPass Summit during the day 1 keynote (viewable online).

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This is very interesting news for me, thank you. – Michał Herman Dec 6 '12 at 19:27

The hybrid approach is often used, with many of the main DB vendors having a complimentary in-memory database to synchronise with their traditional database:

  • Oracle have timesten, which can integrate with Oracle DB
  • MySQL is commonly used with memcached
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