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https://issues.apache.org/jira/browse/HIVE-18252?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16286676#comment-16286676
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Jason Dere commented on HIVE-18252:
-----------------------------------
[~ashutoshc] can you review?
> Limit the size of the object inspector caches
> ---------------------------------------------
>
> Key: HIVE-18252
> URL: https://issues.apache.org/jira/browse/HIVE-18252
> Project: Hive
> Issue Type: Bug
> Components: Types
> Reporter: Jason Dere
> Assignee: Jason Dere
> Attachments: HIVE-18252.1.patch
>
>
> Was running some tests that had a lot of queries with constant values, and
> noticed that ObjectInspectorFactory.cachedStandardStructObjectInspector
> started using up a lot of memory.
> It appears that StructObjectInspector caching does not work properly with
> constant values. Constant ObjectInspectors are not cached, so each constant
> expression creates a new constant ObjectInspector. And since object
> inspectors do not override equals(), object inspector comparison relies on
> object instance comparison. So even if the values are exactly the same as
> what is already in the cache, the StructObjectInspector cache lookup would
> fail, and Hive would create a new object inspector and add it to the cache,
> creating another entry that would never be used. Plus, there is no max cache
> size - it's just a map that is allowed to grow as long as values keep getting
> added to it.
> Some possible solutions I can think of:
> 1. Limit the size of the object inspector caches, rather than growing without
> bound.
> 2. Try to fix the caching to work with constant values. This would require
> implementing equals() on the constant object inspectors (which could be slow
> in nested cases), or else we would have to start caching constant object
> inspectors, which could be expensive in terms of memory usage. Could be used
> in combination with (1). By itself this is not a great solution because this
> still has the unbounded cache growth issue.
> 3. Disable caching in the case of constant object inspectors since this
> scenario currently doesn't work. This could be used in combination with (1).
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