[jira] [Commented] (CALCITE-2717) Cached traits in RelTraitDef's canonicalMap can't be garbage-collected

["Haisheng Yuan (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CALCITE-2717?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16704311#comment-16704311 ] 

Haisheng Yuan commented on CALCITE-2717:
----------------------------------------

We have seen the OOM issue accidentally in our system because the cache is not garbage-collected as expected. To avoid this issue, we can specify the cache's maximum entry size, which I don't like. We can also change the cache loader to return the clone of the key, like this:
{code:java}
CacheBuilder.newBuilder()
    .softValues()
    .build(CacheLoader.from(key -> key.clone()));
{code}
But we have to make RelTrait extend Cloneable interface.

[~julianhyde] thoughts?

> Cached traits in RelTraitDef's canonicalMap can't be garbage-collected 
> -----------------------------------------------------------------------
>
>                 Key: CALCITE-2717
>                 URL: https://issues.apache.org/jira/browse/CALCITE-2717
>             Project: Calcite
>          Issue Type: Bug
>          Components: core
>            Reporter: Haisheng Yuan
>            Assignee: Julian Hyde
>            Priority: Major
>
> Softly-referenced objects will be garbage-collected in a globally least-recently-used manner, in response to memory demand. Even though canonicalMap's value is soft referenced, key is strong referenced, key and value are referencing the same object. So traits in the cache will never be garbage-collected, which may cause OOM if we have tons of different traits.



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