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From Kunal Khatua <kkha...@mapr.com>
Subject RE: Drill session and jdbc connections
Date Thu, 14 Dec 2017 07:09:39 GMT
That will (IMO) not solve the problem, since different threads will be setting and resetting
the store format. My suggestion would be to use a pool of connections and each thread work
off one connection, and returning it to the pool when done resetting. 

-----Original Message-----
From: Rahul Raj [mailto:rahul.raj@option3consulting.com] 
Sent: Wednesday, December 13, 2017 10:23 PM
To: user@drill.apache.org
Subject: Re: Drill session and jdbc connections

We are using a one connection and multiple statements for creating the CSV files. I will surround
the calls with a finally to reset the store format.

Thanks for your inputs,

Regards,
Rahul

On Wed, Dec 13, 2017 at 10:59 PM, Kunal Khatua <kkhatua@mapr.com> wrote:

> A Drill session is isolated and bound to a connection. Your 
> 'getConnection()' method might be fetching connections from a pool, 
> where the settings haven't been reset. If the connections are shared, 
> you will continue to have this problem.
>
> If you are returning a connection back to the pool, run the RESET 
> command to ensure the default state is set.
>
> https://urldefense.proofpoint.com/v2/url?u=https-3A__drill.apache.org_
> docs_reset_&d=DwIBaQ&c=cskdkSMqhcnjZxdQVpwTXg&r=-cT6otg6lpT_XkmYy7yg3A
> &m=ZvNYB-8v46AopTz4m3cYOACJ-OZevKaxg0jBJBBq2MQ&s=-DeteEKKw3vUytwB7ZEVn
> yDMb5mIeceotKszFZsjSjE&e=
>
>
>
> -----Original Message-----
> From: Rahul Raj [mailto:rahul.raj@option3consulting.com]
> Sent: Wednesday, December 13, 2017 2:17 AM
> To: user@drill.apache.org
> Subject: Drill session and jdbc connections
>
> Hi,
>
> How is a drill session related to a drill jdbc connection instance? 
> What happens in a pool of connections when one connection changes the 
> store.format? I am seeing some mix-ups where a parquet row is written 
> as an array of multiple records(rather than multiple columns) when 
> another thread tries to create a csv file. This happens only during 
> the race condition between CSV and parquet formats.
>
> Scenario:
>
> Thread 1 for CSV creation:
>
> Connection conn = getConnection();
> conn.execute("ALTER SESSION SET `store.format`='csv'") 
> conn.execute("CREATE TABLE someparquet AS ...") conn.execute("ALTER 
> SESSION SET `store.format`='parquet'")
>
> Thread 2 for parquet creation:
>
> Connection conn = getConnection();
> conn.execute("CREATE TABLE somecsv AS ...")
>
> In thread 2, the parquet gets written as an ARRAY with all the fields 
> because of the side effect of Thread 1 setting format as CSV when they 
> execute in parallel.
>
> Is it possible to have session isolation in this situation?
>
> Regards,
> Rahul
>
> --
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