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From Sergi Vladykin <sergi.vlady...@gmail.com>
Subject Re: Performance of join SQL queries
Date Mon, 10 Aug 2015 23:52:35 GMT

This stuff is not quite yet documented, (I'm going to fix this soon) so
I'll answer here.

Basically Ignite SQL works the following way:

It receives SQL query parses it into AST, then splits this query in two
map and reduce. Map query runs on each participating cache node, reduce
query aggregates results received from all nodes running map query.
In reduce query you will see function __Z0() which is basically
a function that returns results of map queries from all the nodes.

Currently you will see only two statements in explain, but this is going to
change soon
and Ignite will be able to cut the original query into more parts.
in reduce query you will see multiple artificial tables __T0,__T1 ... __TN
depending on query structure.


P.S. Your questions are quite relevant, I think I will be writing docs
looking at this thread,
so feel free to ask more, I will be happy to help!

2015-08-10 12:09 GMT+03:00 alex.glau <alex.glau@gmail.com>:

> Sergi, you are right: with new version of Ignite it waked good.
> I am afraid to be too bothering, but I need a little bit more information
> about reducing node and map node in order to understand two statements
> obtained from EXPLAIN query.
> Please point me to relevant documentation.
> Thank you. I'm really appreciate you quick and useful help.
> --
> View this message in context:
> http://apache-ignite-users.70518.x6.nabble.com/Performance-of-join-SQL-queries-tp845p884.html
> Sent from the Apache Ignite Users mailing list archive at Nabble.com.

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