Pradeep Kamath updated PIG-636:

    Attachment: PIG-636-v2.patch

Attached new version of patch with the following two changes as per review 
1) SingleTupleBag now only has one constructor which takes the tuple the bag is 
meant to contain. This way SingleTupleBags can only be created with the member 
2) size() now returns 1.

> PERFORMANCE: Use lightweight bag implementations which do not register with 
> SpillableMemoryManager with Combiner
> ----------------------------------------------------------------------------------------------------------------
>                 Key: PIG-636
>                 URL: https://issues.apache.org/jira/browse/PIG-636
>             Project: Pig
>          Issue Type: Improvement
>    Affects Versions: types_branch
>            Reporter: Pradeep Kamath
>            Assignee: Pradeep Kamath
>             Fix For: types_branch
>         Attachments: PIG-636-v2.patch, PIG-636.patch
> Currently whenever Combiner is used in pig, in the map, the 
> POPrecombinerLocalRearrange operator puts the single "value" tuple 
> corresponding to a key into a DataBag and passes this to the foreach which is 
> being combined. This will generate as many bags as there are input records. 
> These bags all will have a single tuple and hence are small and should not 
> need to be spilt to disk. However since the bags are created through the 
> BagFactory mechanism, each bag creation is registered with the 
> SpillableMemoryManager and a weak reference to the bag is stored in a linked 
> list. This linked list grows really big over time causing unnecessary Garbage 
> collection runs. This can be avoided by having a simple lightweight 
> implementation of the DataBag interface to store the single tuple in a bag. 
> Also these SingleTupleBags should be created without registering with the 
> spillableMemoryManager. Likewise the bags created in POCombinePackage are 
> supposed to fit in Memory and not spill. Again a NonSpillableDataBag 
> implementation of DataBag interface which does not register with the 
> SpillableMemoryManager would help.

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