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://apacheignite-sql.readme.io/docs/distributed-joins
[2] https://github.com/hostettler/igniteParallelQueries/pull/1
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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?
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