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From "Aman Sinha (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DRILL-3735) Directory pruning is not happening when number of files is larger than 64k
Date Sat, 12 Sep 2015 16:19:45 GMT

    [ https://issues.apache.org/jira/browse/DRILL-3735?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14742112#comment-14742112
] 

Aman Sinha commented on DRILL-3735:
-----------------------------------

Let's treat the 64K limit issue separate from the multi-phase directory pruning.  For the
multi-phase pruning I have opened a separate enhancement: DRILL-3759.   I believe the 64K
limit is more urgent - especially considering the CTAS auto partitioning creates files in
a flat structure, not hierarchical - so we'll try to address it first.  

My proposal is to have the PartitionDescriptor implement the Iterable interface and use the
{code}com.google.common.collect.Lists.partition(List<T> list, int size){code} method
to subdivide the list into chunks of 64K each (last sublist could be smaller).  The iterator
will return sublists to the PruneScanRule which will then iterate within the sublists and
perform the same logic as before except that the VectorContainer used by the rule will be
cleared out after each sublist is processed.   The final output list of files is already stored
in a List on the heap and I am not proposing to change that. 


> Directory pruning is not happening when number of files is larger than 64k
> --------------------------------------------------------------------------
>
>                 Key: DRILL-3735
>                 URL: https://issues.apache.org/jira/browse/DRILL-3735
>             Project: Apache Drill
>          Issue Type: Bug
>          Components: Query Planning & Optimization
>    Affects Versions: 1.1.0
>            Reporter: Hao Zhu
>            Assignee: Aman Sinha
>
> When the number of files is larger than 64k limit, directory pruning is not happening.

> We need to increase this limit further to handle most use cases.
> My proposal is to separate the code for directory pruning and partition pruning. 
> Say in a parent directory there are 100 directories and 1 million files.
> If we only query the file from one directory, we should firstly read the 100 directories
and narrow down to which directory; and then read the file paths in that directory in memory
and do the rest stuff.
> Current behavior is , Drill will read all the file paths of that 1 million files in memory
firstly, and then do directory pruning or partition pruning. This is not performance efficient
nor memory efficient. And also it can not scale.



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