MySQL Cluster: Difference between revisions

Revision as of 22:31, 4 August 2006

Revision as of 05:46, 20 September 2006

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==Limitations==

The largest limitation currently is with the fact that it is largely an [[in-memory database]]. All indexeddata columns resideresides entirely in [[Primary storage|primary memory]]. This means that across the cluster setup, you need enough [[Random access memory|RAM]] to store muchthe entire dataset. The memory usage can be additive across Data nodes. For instance, with two replicas and four data nodes, the total amount of RAM needed is 1/2 the entiretotal datasetsize of the Data. In the 5.1 release, non indexed columns can be stored on disk and don't require dedicated RAM. In 5.1, all indexes still need to be in main memory though.

Another limitation is with how many nodes can be part of the cluster. Currently you can only have up to 64 nodes in the cluster with up to 48 of those being data nodes that store the actual data. It is possible to change this at compile time, but that has not been thoroughly tested at this point.

Versions up to and including 5.0 do not have support for variable width fields, instead using the entire storage size of the column declaration, effectively making a varchar(255) into a char(255). 5.1 adds true varchar support.

Also of note, The current maximum number of metadata objects is limited to 1,600. (including database tables, system tables, indexes, etc.)