[erlang-questions] MNesia Distribution Questions

Ulf Wiger ulf.wiger@REDACTED
Wed Oct 21 19:06:20 CEST 2009

Rob Stewart wrote:
> 1. And example - I have a compex query to apply to a dataset, of, say
> 10,000,000 rows in an MNesia database. This database is replicated over 10
> nodes in a network. Will the query be split for equal computation to each of
> the 10 nodes, or will the query be executed on either one random or one
> selected MNesia node.

If it's one homogeneous table that is simply replicated across all 
nodes, the query will be executed on the originating node only.

If the table is fragmented, a subset of fragments will be identified
(if the whole key isn't bound, this will be all fragments), and the
query will be executed on all fragments in parallel. The resulting
sets will be merged, respecting the ordering semantics of the table
(i.e. sorted if it's an ordered_set table, otherwise not).

Ulf W
Ulf Wiger
CTO, Erlang Training & Consulting Ltd

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