Talk:In-memory database: Difference between revisions

Revision as of 02:35, 15 January 2012

Revision as of 10:26, 18 February 2013

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Data in memory is not a particular feature of IMMDB: it is misleading to suggest that it is. <span style="font-size: smaller;" class="autosigned">— Preceding [[Wikipedia:Signatures|unsigned]] comment added by [[Special:Contributions/120.148.48.44|120.148.48.44]] ([[User talk:120.148.48.44|talk]]) 02:34, 15 January 2012 (UTC)</span><!-- Template:Unsigned IP --> <!--Autosigned by SineBot-->

== Couchbase and hybrid on-disk/in-memory databases ==

I have [https://en.wikipedia.org/w/index.php?title=In-memory_database&diff=538854332&oldid=538686621 removed] the paragraph about Couchbase from this article. The editor describes it as a "hybrid In-Memory and File-based database system". All I found from the [http://www.couchbase.com/docs/couchbase-manual-2.0/couchbase-bestpractice-clusterdesign.html Couchbase documentation is this]:

:''Couchbase is well suited for applications that want most of its active dataset in memory. This data that is actively used at any given point in time is called the Working Set. It is very important that you allocate enough memory for the entire Working Set to live in memory. When there is not enough memory left for the new data that is written, some values are ejected from memory and will only exist on disk. Accessing values from disk is much slower than accessing data in memory''

Which describes the sort of write buffering/read caching behavior that also happens in every other modern database. It all boils down to how "In-memory database" is defined. Some examples:

* PostgreSQL has the "synchronous_commit" option; when turned off, then database writes/commits are acknowledged to the client while they still exist only in memory, before written to disk -- just like Couchbase. Does this make PostgreSQL an in-memory database?

* If I run PostgreSQL on a Linux [[tmpfs]] in-memory file system, is it correct to call it an in-memory database?

* If my application only uses the MySQL "memory" storage engine, should I call MySQL an in-memory database?

I would say the only reasonable answer to these questions is "no" -- otherwise we will need to include every modern database engine under the sun, which defeats the purpose of the "in-memory database" distinction. -- [[user:intgr|intgr]]&nbsp;<small>[[user talk:intgr|[talk]]]</small> 10:26, 18 February 2013 (UTC)