drill-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Aman Sinha <amansi...@apache.org>
Subject Re: How to verify predicate pushdown
Date Thu, 26 Oct 2017 17:30:10 GMT
For simple AND-ed predicates, if the entire filter is eligible for pushdown
then after pushdown the filter would be dropped, so the Explain plan will
not show a Filter node.  In this case, I would expect the row count of the
Scan to be reduced.  For complex predicates, e.g combination of ANDs and
ORs or ones which involve expressions such as CAST etc.,  it is possible
some part of the filter would be pushed into the Scan but the Filter node
will remain.   In this case, the row count of the Scan would not be reduced
to avoid doing the reduction twice.


-Aman


On Thu, Oct 26, 2017 at 5:33 AM, PROJJWAL SAHA <proj.saha@gmail.com> wrote:

> Hello,
>
> One question,
> How to verify whether predicate pushdown is happening ?
>
> I have one parquet file generated using CTAS command. I have executed
> REFRESH METADATA.  I am firing a simple query with a WHERE clause. In the
> physical plan for the scan operation, i see rowcount as total number of
> rows in the data. Should this value gets lowered in case of predicate
> pushdown ? Is is necessary to sort the predicate column for this to take
> effect ? Any pointers ?
>
> Regards,
> Projjwal
>

Mime
  • Unnamed multipart/alternative (inline, None, 0 bytes)
View raw message