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https://issues.apache.org/jira/browse/PIG-2293?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13118256#comment-13118256
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Daniel Dai commented on PIG-2293:
---------------------------------
I discussed with Ashutosh (the author of regular MergeJoin) and tried
DefaultIndexableLoader. It works fine in merge-sparse join. We do need to
remove the DefaultIndexableLoader restriction. It is very confusing if one
loader supports merge-sparse and the other don't, even when both loader
implemented the same interface.
> Pig should support a more efficient merge join against data sources that
> natively support point lookups or where the join is against large, sparse
> tables.
> ----------------------------------------------------------------------------------------------------------------------------------------------------------
>
> Key: PIG-2293
> URL: https://issues.apache.org/jira/browse/PIG-2293
> Project: Pig
> Issue Type: New Feature
> Components: impl
> Affects Versions: 0.9.0
> Reporter: Aaron Klish
> Assignee: Aaron Klish
> Fix For: 0.10
>
> Attachments: PIG-2293-1.patch, PIG-2293-2.patch, e2e_test.txt,
> patch.txt, patch.txt
>
> Original Estimate: 336h
> Remaining Estimate: 336h
>
> The existing PIG merge join has the following limitations:
> 1. It assumes the right side of the table must be accessed sequentially -
> record by record.
> 2. It does not perform well against large, sparse tables.
> The current implementation of the merge join introduced the interface
> IndexableLoadFunc. This 'LoadFunc'
> supports the ability to 'seekNear' a given key (before reading the next
> record).
> The merge join physical operator only calls 'seekNear' for the first key in
> each split (effectively eliminating splits
> where the first and subsequent keys will not be found). Subsequent joins are
> found by reading sequentially through
> the records on the right table looking for matches from the left table.
> While this method works well for dense join tables - it performs poorly
> against large sparse tables or data sources that support
> point lookups natively (HBase for example).
> The proposed enhancement is to add a new join type - 'merge-sparse' to PIG
> latin. When specified in the PIG script, this join type
> will cause the merge join operator to call seekNear on each and every key
> (rather than just the first in each split).
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