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From Jinfeng Ni <...@apache.org>
Subject Re: Drill Join query optimization
Date Fri, 04 Nov 2016 19:03:20 GMT
I'm not familiar with Mongo storage plugin. But looking at the code,
seems there is a MongoPushDownFilterForScan rule, which should be able
to push the filter ta.Id ='123' into TableA. If your query plan does
not show this filter is pushed down into Mongo Scan operator, there
might be a bug in this rule.

For the filter pushdown on TableB side, it's related to filter created
from transitive closure. Looks like Drill does not enable such rule.
As such, we do not create  tb.Id='123', from ta.Id = tb.Id and
ta.id='123'. Such rule should be independent from Mongo storage
plugin, and should work for any storage plugin.

[1] https://github.com/apache/drill/blob/master/contrib/storage-mongo/src/main/java/org/apache/drill/exec/store/mongo/MongoPushDownFilterForScan.java

On Fri, Nov 4, 2016 at 4:28 AM, Khurram Faraaz <kfaraaz@maprtech.com> wrote:
> What version of Drill are you on ?
> Can you please share the query plan for your query ?
> Please share the table definitions ?
> Is this a standalone setup or cluster of Drillbits ?
> On Fri, Nov 4, 2016 at 2:23 PM, <Mridul.Chopra@rbs.com.invalid> wrote:
>> Hello,
>> I am working on a proof of concept to optimize the performance of the
>> join queries executed through drill. The underlying storage is a NO-SQL
>> based database - Mongo DB. The time it takes to return the result of the
>> join query is very high (46 seconds). Upon further analysis, as per the
>> physical plan of the query it is observed that both the left side (15 lakh
>> records) and right side table (13 lakh) are fully scanned and it takes 24
>> seconds and 20 seconds respectively for the same.
>> Here is the query -
>> select ta.[SOME_COLUMN] from mongo.Test.TABLEA ta INNER JOIN
>> mongo.Test.TABLEB ta ON ta.Id = tb.Id and ta.Id ='123'
>> Records in table A : 15 Lakhs
>> Records in table B : 13 Lakhs
>> Filter condition : Id is indexed field in both the tables (ascending)
>> Drill Plan shows Hash-join being performed as shown in the plan (as
>> attached above)
>> I have the following questions -
>> 1)     Why does drill fetch all the records into the memory even though
>> filter condition on the indexed column was provided for one of the table ?
>> 2)     If the Drill planner/optimizer is intelligent then records could
>> have been filtered on the second table as well based on the join condition
>> (to reduce the dataset and hence result in faster execution time)
>> 3)     Are there any performance tuning options available to bring down
>> the query response time and generate a better query plan ?
>> I would appreciate if you can provide me pointers/directions or answers to
>> the above questions.
>> Please feel free if you need any additional information.
>> Thanks,
>> Mridul
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