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From Max Timonin <timonin.ma...@gmail.com>
Subject [DISCUSSION] Fail on non-colocated join
Date Tue, 02 Feb 2021 15:18:02 GMT
Hi, Igniters!

Last week I investigated a bug [1]. It's about an incorrect result for
non-colocated joins. For such joins it's required to set up the
"distributedJoin" flag, or try to make joined tables colocated. It is
covered in docs [2]. But it's not obvious and some users don't read that or
forget about that. In result there are wrong results for some queries that
are pretty hard to debug.

There is a ticket [3] with a comment, where it's suggested to add a check
for such joins. I tried to implement it and found a place where it's
possible to put this check. But there is an open question what this check
should do. Currently I see 2 ways for that:
1. Forbid non-colocated joins that aren't marked with the distributedJoin
flag, and throw an exception.
2. Check every query for such joins and implicitly setup a distributedJoin
flag for them.

Both solutions may break compatibility, but is this compatibility OK?

Igniters, what do you think?

[1] https://issues.apache.org/jira/browse/IGNITE-12847
[2]
https://ignite.apache.org/docs/latest/SQL/distributed-joins#distributed-joins
[3] https://issues.apache.org/jira/browse/IGNITE-13019

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