Vladimir Ozerov created IGNITE-8596:
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Summary: SQL: remove unnecessary index lookups when query
parallelism is enabled
Key: IGNITE-8596
URL: https://issues.apache.org/jira/browse/IGNITE-8596
Project: Ignite
Issue Type: Task
Components: sql
Affects Versions: 2.5
Reporter: Vladimir Ozerov
Fix For: 2.6
See
{{org.apache.ignite.internal.processors.query.h2.twostep.GridMapQueryExecutor#onQueryRequest}}
method. If table is segmented, we will submit as many SQL requests as much
segments. But consider a case when target cache partition(s) is already defined
by user or derived through partition pruning. In this case most of segments
will not contain useful information and return empty result set. At the same
time these queries may impose index or data page scans, thus consuming
resources without a reason.
To mitigate the problem we should not submit SQL requests to segments we are
not interested in.
Note that it is not sufficient to simply skip SQL requests on mapper, because
reducer expects separate response for every message. We should fix both local
mapper logic as well as protocol.
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