August 20, 2012

In-memory, (hybrid) memory-centric DBMS — three analytic glossary draft entries

These are three closely-related draft entries for the DBMS2 analytic glossary. Please comment with any ideas you have for their improvement!

1. We coined the term memory-centric data management to comprise several kinds of technology that manage data in RAM (Random Access Memory), including:

Related link

2. An in-memory DBMS is a DBMS designed under the assumption that substantially all database operations will be performed in RAM (Random Access Memory). Thus, in-memory DBMS form a subcategory of memory-centric data management systems.

Ways in which in-memory DBMS are commonly different from those that query and update persistent storage include:

If what otherwise appears to be an in-memory DBMS routinely queries data from disk, then we refer to it as being hybrid memory-centric. However, even true in-memory DBMS may copy data into persistent storage, so as to keep it safe.

Examples of in-memory DBMS include:

3. Hybrid memory-centric DBMS is our term for a DBMS that has two modes:

It is difficult to make the boundaries of this category precise, because:

That said, we prefer to reserve the term “hybrid memory-centric” for DBMS designed according to the same principles as in-memory DBMS, for example IBM solidDB.

Hybrid memory-centric DBMS form a subcategory of memory-centric data management systems.


6 Responses to “In-memory, (hybrid) memory-centric DBMS — three analytic glossary draft entries”

  1. Rob Klopp on August 20th, 2012 3:07 pm

    I wonder if the key here is that the DBMS explicitly manages data in memory as opposed to implicit management via buffers of via the OS? Explicit management might include some of the concepts you suggest like reduced locking or like techniques to increase utilization of the CPU caches.

    Question: If Postgres was disk-based but added explicit management of some data in-memory does it become a hybrid? If HANA added a disk-based data management layer would it become a hybrid?

  2. Curt Monash on August 20th, 2012 3:53 pm


    If there’s a disk-based layer we should say it becomes a hybrid.

    As for explicit vs. implicit memory management — good idea, but I’m concerned about going down the rabbit hole of ascertaining which DBMS does exactly what, and how much benefit it gives them.

    All this will be clearer if I also put in an entry for memory mapping, actually. A lot of DBMS that happen to often be used with their working sets in RAM are the ones that get data on and off disk by delegating the problem to the OS via memory mapping. At least, I think that’s how memory mapping works …

  3. Kenton Andersen on August 22nd, 2012 4:52 pm


    Thanks for taking the time to develop the glossary. I think this is going to be useful for a long time.

    I recommend that at some point, you consider how flash memory is going to alter the in-memory vs. persistent storage tradeoffs. In a few years, all databases might qualify as “hybrid”, and the idea of needing a RAM-centric variant for performance may seem quaint.

  4. Brad JS Lim on September 6th, 2012 4:26 am

    Dear all,
    I’m working at Altibase Corporation.
    If you have a question of In memory DBMS as well as Hybrid DBMS (Memory + Disk DBMS), send us by email.

    ALTIBASE Provides fast, reliable, data management systems in all kinds of business critical operating systems.

    In your memory…

  5. Data warehouse appliance — analytic glossary draft entry | DBMS 2 : DataBase Management System Services on October 12th, 2012 1:29 am

    […] focus on in-memory database operations; memory-centric systems are not commonly referred to as “data warehouse […]

  6. Notes on memory-centric data management | DBMS 2 : DataBase Management System Services on January 3rd, 2014 4:35 am

    […] coined “memory-centric” as an alternative. Then I relented 1 1/2 years ago, and defined in-memory DBMS as DBMS designed under the assumption that substantially all database operations will be performed […]

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