[jira] [Commented] (TOREE-374) Variables declared on the Notebook are not garbage collected

["Marius Van Niekerk (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/TOREE-374?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15854673#comment-15854673 ] 

Marius Van Niekerk commented on TOREE-374:
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So this is largely due to how the scala repl works.   Each complete block of code that is evaluated corresponds to a class that gets created. There isn't a particularly simple way to denote that a particular cell / code block is no longer needed. 

For long running notebooks users should use the comm api rather than reexecuting cells. 

> Variables declared on the Notebook are not garbage collected
> ------------------------------------------------------------
>
>                 Key: TOREE-374
>                 URL: https://issues.apache.org/jira/browse/TOREE-374
>             Project: TOREE
>          Issue Type: Bug
>    Affects Versions: 0.1.0
>            Reporter: David Taieb
>
> I'm not sure if it's a bug or a limitation of the underlying scala REPL.
> As part of supporting PixieDust (https://github.com/ibm-cds-labs/pixiedust) auto-visualization feature within Scala gateway, I have implemented a weak hashmap that tracks objects declared on the Scala REPL. However, I have found that objects are not correctly gc'ed when the object is declared in a cell with a val or var keyword and then the cell is ran again. One would expect that the original object has no more references and should be gc'ed but it's not. 
> However, when the object is declare with var keyword and then set to null in another cell, then it is correctly gc'ed.
> I'm concerned that users who run the same cell multiple times would unwittingly have memory leaks which can eventually lead to OOM errors.



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