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https://issues.apache.org/jira/browse/IGNITE-6202?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Vladimir Ozerov updated IGNITE-6202:
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Labels: performance sql-engine (was: performance)
> SQL: support hash join
> ----------------------
>
> Key: IGNITE-6202
> URL: https://issues.apache.org/jira/browse/IGNITE-6202
> Project: Ignite
> Issue Type: Task
> Components: sql
> Affects Versions: 2.1
> Reporter: Vladimir Ozerov
> Priority: Major
> Labels: performance, sql-engine
>
> Justification is the same as for IGNITE-6201 (merge joins). If join is
> equijoin, and participating attributes are not sorted in advance, then
> instead of executing nested loops, we can do the following:
> 1) Get the table with smaller number of entries
> 2) Build a hash table from target attribute to the list of matching entries
> 3) Iterate over larger table and perform lookup into hash table
> Note that this operation might be memory-intensive in case smaller table is
> large enough still. For this reason we should provide a mechanism to avoid
> out-of-memory errors. Let's avoid spilling to disk in the first iteration,
> and try to set a kind of hard limit on how much data can be kept in memory.
> If we see that this limit cannot be satisfied, then fallback to nested loops.
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