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From "Vladimir Ozerov (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (IGNITE-6202) SQL: support hash join
Date Wed, 21 Mar 2018 13:01:00 GMT

     [ https://issues.apache.org/jira/browse/IGNITE-6202?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Vladimir Ozerov updated IGNITE-6202:
------------------------------------
    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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