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From "Kunal Khatua" <ku...@apache.org>
Subject Re: Performace issue
Date Tue, 12 Feb 2019 18:01:52 GMT
You'll need to edit the memory settings in DRILL_HOME/conf/drill-env.sh 
I suspect that your 5MB JSON data might be having a lot of objects, which need to be serialized
in memory.

FLATTEN has the problem that it replicates the data parent data for each child node that is
being flattened into a row... so the resulting data being constructed in memory can grow significantly. 
One way to work around (not elegant, but worth trying) would be to generate intermediate
flatten data and write temporary (if not using WebUI) tables and keep flattening out those
records until you have a fully flattened dataset to work with directly.

On 2/11/2019 10:37:58 PM, PRAVEEN DEVERACHETTY <praveendk@gmail.com> wrote:
Thnks a lot Kunal. I am looking into that. I have one observation.

With out flatten also, i tried to run a query of size 5MB, it is taking 5GB
of heap? how do i control heap? Are there any settings i can modify. i am
reading a lot, but nothing is working for me. It would be helpful how to
control heap, i modified memory parameters based on the documentation, it
is not working yet. it would be really helpful if i get some help in this
regard. Thanks in advance.


On Tue, Feb 12, 2019 at 11:18 AM Kunal Khatua wrote:

> This is a good starting point for understanding LATERAL-UNNEST and how it
> compares to the FLATTEN operator.
> https://drill.apache.org/docs/lateral-join/
> On 2/11/2019 9:03:42 PM, PRAVEEN DEVERACHETTY wrote:
> Thanks Kunal.
> i am not getting how to use lateral-unrest as dataset does not have child
> rows. All data is in array of json objects(as mentioned below). There are
> two json objects separated by comma and enclosed in squre bracket.
> [{"Location":"100","FirstName":"test1"},{"Location":"100","FirstName":"test2"},{"Location":"101","FirstName":"test3"}]
> We are using drill from Java. Through a rest invocation. Not using json
> files. All data is sent over post as string. We are using convert_from
> function in the query to convert into json objects. As we are sending array
> of json objects, using FLATTEN operator to convert into multiple rows. is
> there any way to avoid Flatten, as we see huge spike for 54MB data, going
> to 24GB and still failing with heap error. not sure what is wrong. Can i
> use FLATTEN on the entire data set? There are almost 54K records that is
> getting FLATTENED.
> example query: 1)first converted into array of json objects 2) flatten to
> convert into multiple rows
> select ems.* from (select flatten(t.jdata) as record from (select
> convert_from('[{"Location":"100","FirstName":"test1"},{"Location":"100","FirstName":"test2"},{"Location":"101","FirstName":"test3"}..]')
> as jdata) as t) ems
> On Sat, Feb 9, 2019 at 1:37 AM Kunal Khatua wrote:
> > The memory (heap) would climb as it tries to flatten the JSON data. Have
> > you tried looking at Drill's LateralJoin-Unnest feature? It was meant to
> > address memory issues for some use cases of the FLATTEN operator.
> >
> > On 2/8/2019 5:17:01 AM, PRAVEEN DEVERACHETTY wrote:
> > I am running a query with UNION ALL. as below
> >
> > select
> > from ( select FLATTEN(t.jdata) as record from
> > ((select convert_from(json string, json) union all
> > (select conver_from(json_string,json) union all
> > ...
> > ) as jdata) ) as t) ems
> >
> > Reason for giving union all is because we are invoking a call using rest
> > app, there is limitation of 20,000 when we use convert_from function. Our
> > heap size is 8GB, server is 8core. From profiling, it shows this
> perticula
> > query spikes from 100MB to 8GB continuously. is there anything i am
> > doing wrong?.
> >
> > Thanks,
> > Prveen
> >

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