Hi Anil, Group by queries with collocate = true will be correct if: for every group there is only partition that contains all data of this group. Ignite does not know if group data is collocated for a query, so with this option we can give a hint to Ignite.
For example: In this case, we can make grouping and apply Having condition on map stage, that results in reducing network traffic. For non-collocated groups we can't apply Having on map stage as we have only part of data at this time. So, in this case with collocate = true we can get wrong results. On Tue, Feb 7, 2017 at 6:29 AM, Anil <[email protected]> wrote: > Hi, > > May I know what do you mean by "When used incorrectly" ? > > group by queries with collocate = true is not incorrect usage or i > misunderstood this ? > > Thanks. > > On 7 February 2017 at 01:26, vkulichenko <[email protected]> > wrote: > >> Well, I would agree that the flag is confusing, but your understanding is >> not >> correct. When used incorrectly, this flag does breaks query result because >> it forces Ignite to change execution plan to more optimal. This >> optimization >> doesn't always work though (that's actually the reason why it's >> configurable). >> >> -Val >> >> >> >> -- >> View this message in context: http://apache-ignite-users.705 >> 18.x6.nabble.com/NOT-IN-in-ignite-tp9861p10458.html >> Sent from the Apache Ignite Users mailing list archive at Nabble.com. >> > > -- Best regards, Andrey V. Mashenkov
