Hi Roman, Thanks a lot for the answer (and the pull request). As I said initially, I was under the impression that the reason was the lack of affinity. I understand the reason and the current design and I think we all agreed that this is not optimal and that it should be reworked in the new design. Especially the sort of silent behavior. That being said, more than a warning : having joins in // inter partitions would be very helpful but I understand that it is not straightforward.
As always you guys are very reactive and helpful. Keep up the great work. Appreciate it. -----Original Message----- From: Roman Kondakov <kondako...@mail.ru.INVALID> Sent: Monday, November 18, 2019 11:04 AM To: dev@ignite.apache.org Subject: Re: New SQL execution engine Hi, Steve This behavior is actually not a bug, but this is not obvious. I'll try to explain. When query parallelism = N is turned on, it means that each cache is divided into N parts from the SQL point of view. Every SQL query is executed independently over each particular part, and then results are merged together during the reducer step. This is absolutely identical to the distributed query execution, where instead of a single node with query parallelism = N, we have N nodes with query parallelism = 1. SQL query is executed over each partition of data on all nodes and then results are merged on reducer. As we can see, query parallelism is equivalent to the distributed query execution. When we do joins over distributed tables, we need to think about the collocation of data [1]. If data is not collocated, we get a wrong result. This happens silently, which is not good, IMO. I reworked your example a bit in order to impose collocation on the joining key and now join returns correct result [2]. Current approach in configuration and query execution looks very uncomfortable and should be completely redesigned in the new engine. [1] https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fapacheignite-sql.readme.io%2Fdocs%2Fdistributed-joins&data=02%7C01%7CSteve.Hostettler%40wolterskluwer.com%7C68a93ad417fc4e70ed1808d76c0e9f53%7C8ac76c91e7f141ffa89c3553b2da2c17%7C0%7C0%7C637096682368420072&sdata=82bDWI1PHUOzNz95A5F%2Flyiqlrb9aQ2vadxhE%2FK47LM%3D&reserved=0 [2] https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fhostettler%2FigniteParallelQueries%2Fpull%2F1&data=02%7C01%7CSteve.Hostettler%40wolterskluwer.com%7C68a93ad417fc4e70ed1808d76c0e9f53%7C8ac76c91e7f141ffa89c3553b2da2c17%7C0%7C0%7C637096682368420072&sdata=QCvNEKqGGyZYOXQbF0sG0DUCzYJCnKoWleFTMtngcsc%3D&reserved=0 -- Kind Regards Roman Kondakov On 16.11.2019 12:50, steve.hostett...@gmail.com wrote: > Actually I am now wondering whether this is not just a bug and that I > should record it as such. As the behavior is different with and > without the parallelism and there is no warning during execution or in the > api. > > Any thought? > > > > -- > Sent from: > https://nam04.safelinks.protection.outlook.com/?url=http%3A%2F%2Fapach > e-ignite-developers.2346864.n4.nabble.com%2F&data=02%7C01%7CSteve. > Hostettler%40wolterskluwer.com%7C68a93ad417fc4e70ed1808d76c0e9f53%7C8a > c76c91e7f141ffa89c3553b2da2c17%7C0%7C0%7C637096682368420072&sdata= > LzUii%2BuNqHhS1YbFLNwpe7cn6XRRpKrrSO6wS5zNlSU%3D&reserved=0
