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From Rahul Raj <rahul....@option3.io>
Subject Re: Drill JDBC Plugin limit queries
Date Fri, 19 Oct 2018 15:17:18 GMT
I will make the changes and update you.

Regards,
Rahul

On Fri, Oct 19, 2018 at 1:05 AM Vitalii Diravka <vitalii@apache.org> wrote:

> Rahul,
>
> Possibly *JdbcGroupScan* can be improved, for instance by overriding
> *supportsLimitPushdown()* and *applyLimit()* methods,
> *double rows *field can be updated by the limit value.
>
> I've performed the following query: select * from mysql.`testdb`.`table`
> limit 2;
> but the following one is passed to MySQL: SELECT * FROM `testdb`.`table`
>
> https://github.com/apache/drill/blob/master/contrib/storage-jdbc/src/main/java/org/apache/drill/exec/store/jdbc/JdbcRecordReader.java#L187
> So it is definitely should be improved.
>
> *Note:* Changed mailing list to devs.
>
> On Sun, Oct 14, 2018 at 6:30 AM Rahul Raj <rahul.raj@option3.io> wrote:
>
> > Vitalii,
> >
> > Created documentation ticket DRILL-6794
> >
> > How do we proceed on extending the scan operators to support JDBC
> plugins?
> >
> > Regards,
> > Rahul
> >
> > On Sat, Oct 13, 2018 at 6:47 PM Vitalii Diravka <vitalii@apache.org>
> > wrote:
> >
> > > To update the documentation, since that issues were solved by using
> these
> > > properties in connection URL:
> > > defaultRowFetchSize=10000  [1]
> > > defaultAutoCommit=false    [2]
> > > The full URL was there "url": "jdbc:postgresql://
> > >
> > >
> >
> myhost.mydomain.com/mydb?useCursorFetch=true&defaultAutoCommit=false&loggerLevel=TRACE&loggerFile=/tmp/jdbc.log&defaultRowFetchSize=10000
> > > "
> > >
> > > If some issues are still present, it is also reasonable to create
> tickets
> > > to track them.
> > >
> > > [1]
> > >
> > >
> >
> https://mail-archives.apache.org/mod_mbox/drill-user/201808.mbox/%3CCADN0Fn9066hwvu_ZyDJ24tkAoJH5hqXoysCv83z7DdSSfjr-CQ%40mail.gmail.com%3E
> > > [2]
> > >
> > >
> >
> https://mail-archives.apache.org/mod_mbox/drill-user/201808.mbox/%3C0d36e0e6e8dc1e77bbb67bbfde5f5296e290c075.camel%40omnicell.com%3E
> > >
> > > On Sat, Oct 13, 2018 at 3:56 PM Rahul Raj <rahul.raj@option3.io>
> wrote:
> > >
> > > > Should I create tickets to track these issues or should I create a
> > ticket
> > > > to update the documentation?
> > > >
> > > > Rahul
> > > >
> > > > On Sat, Oct 13, 2018 at 6:16 PM Vitalii Diravka <vitalii@apache.org>
> > > > wrote:
> > > >
> > > > > 1. You are right, it means it is reasonable to extend this rule for
> > > > > applying on other Scan operators (or possibly to create the
> separate
> > > > one).
> > > > > 2. There was a question about OOM issues in Drill + PostgreSQL,
> > please
> > > > take
> > > > > a look [1].
> > > > >     Since you are trying to setup this configs, It will be good,
if
> > you
> > > > > create a Jira ticket to add this info to Drill docs [2]
> > > > >
> > > > > [1]
> > > > >
> > >
> https://mail-archives.apache.org/mod_mbox/drill-user/201808.mbox/browser
> > > > > [2] https://drill.apache.org/docs/rdbms-storage-plugin/
> > > > >
> > > > > On Sat, Oct 13, 2018 at 2:21 PM Rahul Raj <rahul.raj@option3.io>
> > > wrote:
> > > > >
> > > > > > Regarding the heap out of error, it could be that the jdbc driver
> > is
> > > > > > prefetching the entire record set to memory. I just had a look
at
> > > > > > JdbcRecordReader, looks like by setting
> > connection#autoCommit(false)
> > > > and
> > > > > a
> > > > > > sufficient fetch size we could force the driver to stream data
as
> > > > > required.
> > > > > > This is how postgres driver works.
> > > > > >
> > > > >
> > > >
> > >
> >
> https://jdbc.postgresql.org/documentation/head/query.html#query-with-cursor
> > > > > >
> > > > > > We will have to see the behaviour of other drivers too.
> > > > > >
> > > > > > Let me know your thoughts here.
> > > > > >
> > > > > > Regards,
> > > > > > Rahul
> > > > > >
> > > > > >
> > > > > > On Sat, Oct 13, 2018 at 3:47 PM Rahul Raj <rahul.raj@option3.io>
> > > > wrote:
> > > > > >
> > > > > > > Hi Vitalii,
> > > > > > >
> > > > > > > There are two concrete implementations of the class -
> > > > > > > DrillPushLimitToScanRule LIMIT_ON_SCAN and
> > > > > > > DrillPushLimitToScanRule LIMIT_ON_PROJECT.
> > > > > > > LIMIT_ON_SCAN has a comment mentioning "For now only applies
to
> > > > > Parquet.
> > > > > > > And pushdown only apply limit but not offset"
> > > > > > >
> > > > > > > Also I enabled debug mode and found LIMIT is not getting
pushed
> > to
> > > > the
> > > > > > > query.
> > > > > > >     LimitPrel(fetch=[11]): rowcount = 11.0, cumulative
cost =
> > {83.0
> > > > > rows,
> > > > > > > 226.0 cpu, 0.0 io, 585728.0 network, 0.0 memory}, id =
261
> > > > > > >       UnionExchangePrel: rowcount = 11.0, cumulative cost
=
> {72.0
> > > > rows,
> > > > > > > 182.0 cpu, 0.0 io, 585728.0 network, 0.0 memory}, id =
259
> > > > > > >         LimitPrel(fetch=[11]): rowcount = 11.0, cumulative
> cost =
> > > > {61.0
> > > > > > > rows, 94.0 cpu, 0.0 io, 0.0 network, 0.0 memory}, id =
257
> > > > > > >           JdbcPrel(sql=[SELECT * FROM
> > "u_g001"."executioniteration"
> > > > > WHERE
> > > > > > > "id" > 360500000 ]): rowcount = 50.0, cumulative cost
= {50.0
> > rows,
> > > > > 50.0
> > > > > > cpu
> > > > > > >
> > > > > > > Regarding the second point, its the java heap getting filled
> with
> > > > jdbc
> > > > > > > results. How do we address this?
> > > > > > >
> > > > > > > Regards,
> > > > > > > Rahul
> > > > > > >
> > > > > > > On Fri, Oct 12, 2018 at 8:11 PM Vitalii Diravka <
> > > vitalii@apache.org>
> > > > > > > wrote:
> > > > > > >
> > > > > > >> Hi Rahul,
> > > > > > >>
> > > > > > >> Drill has *DrillPushLimitToScanRule* [1] rule, which
should do
> > > this
> > > > > > >> optimization, whether the GroupScan supports Limit
Push Down.
> > > > > > >> Also you can verify in debug mode whether this rule
is fired.
> > > > > > >> Possibly for some external DB (like MapR-DB) Drill
should have
> > the
> > > > > > >> separate
> > > > > > >> class for this optimization [2].
> > > > > > >>
> > > > > > >> [1]
> > > > > > >>
> > > > > > >>
> > > > > >
> > > > >
> > > >
> > >
> >
> https://github.com/apache/drill/blob/master/exec/java-exec/src/main/java/org/apache/drill/exec/planner/logical/DrillPushLimitToScanRule.java#L28
> > > > > > >> [2]
> > > > > > >>
> > > > > > >>
> > > > > >
> > > > >
> > > >
> > >
> >
> https://github.com/apache/drill/pull/1466/files#diff-4819b70118487d81bc9c46a04b0eaaa3R37
> > > > > > >>
> > > > > > >> On Fri, Oct 12, 2018 at 3:19 PM Rahul Raj <
> rahul.raj@option3.io
> > >
> > > > > wrote:
> > > > > > >>
> > > > > > >> > Hi,
> > > > > > >> >
> > > > > > >> > Drill does not push the LIMIT queries to external
databases
> > and
> > > I
> > > > > > >> assume it
> > > > > > >> > could be more related to Calcite. This leads to
out of
> memory
> > > > > > situations
> > > > > > >> > while querying large table to view few records.
 Is there
> > > > something
> > > > > > that
> > > > > > >> > could be improved here? One solutions would be
to push
> filters
> > > > down
> > > > > to
> > > > > > >> the
> > > > > > >> > DB and/or combined with some JDBC batch size limit
to flush
> a
> > > part
> > > > > as
> > > > > > >> > parquet.
> > > > > > >> >
> > > > > > >> > Regards,
> > > > > > >> > Rahul
> > > > > > >> >
> > > > > > >> > --
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