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From John Omernik <j...@omernik.com>
Subject Re: Slow query on parquet imported from SQL Server while the external SQL server is down.
Date Thu, 01 Dec 2016 13:46:45 GMT
@Abhishek,

Do you think the issue is related to any storage plugin that is enabled and
not available as it applies to all queries?  I guess if it's an issue where
all queries are slow because the foreman is waiting to initialize ALL
storage plugins, regardless of their applicability to the queried data,
then that is a more general issue (that should still be resolved, does the
foreman need to initialize all plugins before querying specific data?)
 However, I am still concerned that the query on the CTAS parquet data is
specifically slower because of it's source.  @Rahul could you test a
different Parquet table, NOT loaded from the SQL server to see if the
enabling or disabling the JDBC storage plugin (with the server unavailable)
has any impact?  Basically, I want to ensure that data that is created as a
Parquet table via CTAS is 100% free of any links to the source data. This
is EXTREMELY important.

John



On Thu, Dec 1, 2016 at 12:46 AM, Abhishek Girish <abhishek.girish@gmail.com>
wrote:

> Thanks for the update, Rahul!
>
> On Wed, Nov 30, 2016 at 9:45 PM Rahul Raj <rahul.raj@option3consulting.com
> >
> wrote:
>
> > Abhishek,
> >
> > Your observation is correct, we just verified that:
> >
> >    1. The queries run as expected(faster) with Jdbc plugin disabled.
> >    2. Queries run as expected when the plugin's datasource is running.
> >    3. With the datasource down, queries run very slow waiting for the
> >    connection to fail
> >
> > Rahul
> >
> > On Thu, Dec 1, 2016 at 10:07 AM, Abhishek Girish <
> > abhishek.girish@gmail.com>
> > wrote:
> >
> > > @John,
> > >
> > > I agree that this should work. While I am not certain, I don't think
> the
> > > issue is specific to a particular plugin, but the way in a query's
> > > lifecycle, the foreman attempts to initialize every enabled storage
> > plugin
> > > before proceeding to execute the query. So when a particular plugin
> isn't
> > > configured correctly or the underlying datasource is not up, this could
> > > drastically slow down the query execution time.
> > >
> > > I'll look up to see if we have a JIRA for this already - if not will
> file
> > > one.
> > >
> > > On Wed, Nov 30, 2016 at 8:12 AM, John Omernik <john@omernik.com>
> wrote:
> > >
> > > > So just my opinion in reading this thread.  (sorry for swooping in an
> > > > opining)
> > > >
> > > > If a CTAS is done from any data source into Parquet files.... there
> > > should
> > > > be NO dependency on the original data source to query the resultant
> > > Parquet
> > > > files.   As a Drill user, as a Drill admin, this breaks the concept
> of
> > > > least surprise.  If I take data from one source, and create Parquet
> > files
> > > > in a distributed file system, it should just work.  If there are
> > "issues"
> > > > with JDBC plugins or the HBase/Hive plugins in a similar manner,
> these
> > > > needs to be hunted down by a large group of villages with pitchforks
> > and
> > > > torches.  I just can't see how this could be acceptable at any level.
> > The
> > > > whole idea of Parquet files is they are self describing, schema
> > included
> > > > files.... thus a read of a directory of Parquet files should have NO
> > > > dependancies on anything but the parquet files... even the Parquet
> > > > "additions" (such as the METADATA Cache) should be a fail open
> thing...
> > > if
> > > > it exists great, use it, speed things up, but if it doesn't read the
> > > > parquet files as normal (Which I believe is how it operates)
> > > >
> > > > John
> > > >
> > > > On Wed, Nov 30, 2016 at 12:12 AM, Abhishek Girish <
> > > > abhishek.girish@gmail.com
> > > > > wrote:
> > > >
> > > > > Can you attempt to disable to jdbc plugin (configured with
> SQLServer)
> > > and
> > > > > try the query (on parquet) when SQL Server is offline?
> > > > >
> > > > > I've seen a similar issue previously when the HBase / Hive plugin
> was
> > > > > enabled but either the plugin configuration was wrong or the
> > underlying
> > > > > data source was down.
> > > > >
> > > > > On Fri, Nov 25, 2016 at 3:21 AM, Rahul Raj
> > > <rahul.raj@option3consulting.
> > > > > com>
> > > > > wrote:
> > > > >
> > > > > > I have created a parquet file using CTAS from a MS SQL Server.
> The
> > > > query
> > > > > on
> > > > > > parquet is getting stuck in STARTING state for a long time before
> > > > > returning
> > > > > > the results.
> > > > > >
> > > > > > We could see that drill was trying to connect to the MS SQL
> server
> > > from
> > > > > > which the data was imported. The MSSQL server was down, drill
> threw
> > > an
> > > > > > exception "Failure while attempting to load JDBC schema", and
> then
> > > > > returned
> > > > > > the results. While SQL server is running, the query executes
> > without
> > > > > > issues.
> > > > > >
> > > > > > Why is drill querying the DB metadata externally and not the
> > imported
> > > > > > parquets?
> > > > > >
> > > > > > Rahul.
> > > > > >
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