[jira] [Created] (DRILL-2287) Filesystem partitioning is slow

["Adam Gilmore (JIRA)" <ji...@apache.org>]

Adam Gilmore created DRILL-2287:
-----------------------------------

             Summary: Filesystem partitioning is slow
                 Key: DRILL-2287
                 URL: https://issues.apache.org/jira/browse/DRILL-2287
             Project: Apache Drill
          Issue Type: Improvement
          Components: Query Planning & Optimization
    Affects Versions: 0.7.0, 0.8.0
            Reporter: Adam Gilmore
            Assignee: Jinfeng Ni
            Priority: Minor


We have created a number of Parquet files in different directories (e.g. 1, 2, 3, 4) to partition our data on the filesystem.

Assuming we only have 4 directories (1, 2, 3 and 4), when executing a query like:

{code:sql}
select count(*) from dfs.tmp.mydata where dir0 in (1, 2, 3, 4)
{code}

The query is significantly slower than:

{code:sql}
select count(*) from dfs.tmp.mydata
{code}

Looking at the physical plans, it looks like even if dir0 is only in the WHERE clause, it'll emit that from the scan, which then needs an extra step (a projection) to only project through the count (removing dir0).  This appears to be the cause of the slowdown.

To make it even more confusing, if you only select the LAST directory (i.e. in the case, 4), then it has a different physical plan again and seems to use a union-exchange.

Ultimately, the query planner should realise that dir0 is not projected and then once the pushdown filesystem filtering is done, remove dir0 from being emitted from the scan and not require a project.



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