Vladimir Ozerov created IGNITE-6202:
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Summary: 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
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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