Re: insert function runs forever if connection is lost, keeping the table locked

Hi,

i tried again as suggested with additionally

idle_in_transaction_session_timeout 0
in place,
The transaction still gets not released when the client dies.

But with setting it to 6000, the transaction is sucessfully removed after
6 seconds.

But this will probably now kill every open transaction that takes longer
than 6 seconds, right?
Or will it try to contact the client with keep alive first?

Thanks

_________________________________________

Pieter Zieschang

Modis IT Outsourcing GmbH
Kohlgartenstrasse 11, 04315-Leipzig

Amtsgericht Düsseldorf: HRB 78227
Geschäftsführer: Martin Wimmer, Andreas Buchelt

www.modis.de

From: Dave Cramer <pg(at)fastcrypt(dot)com>
To: Pieter Zieschang <pieter(dot)zieschang(at)modis(dot)de>
Cc: List <pgsql-jdbc(at)postgresql(dot)org>
Date: 29.06.2018 16:58
Subject: Re: insert function runs forever if connection is lost,
keeping the table locked
Sent by: davecramer(at)gmail(dot)com

There is a server side config:

idle_in_transaction_session_timeout = 0 # in milliseconds, 0 is
disabled option which would help in this case.

Linux could wait some time before eventually killing the connection

Dave Cramer

davec(at)postgresintl(dot)com
www.postgresintl.com

On 29 June 2018 at 10:54, Pieter Zieschang <pieter(dot)zieschang(at)modis(dot)de>
wrote:
Hi Dave,

yes, the application died completely due to unhandled NPE.

Client is connecting from windows 10.

I would expect the socket closes and the server should notice that, or at
least use the keep alive settings and detect it after 6 seconds.

Thanks

_________________________________________

Pieter Zieschang

Modis IT Outsourcing GmbH
Kohlgartenstrasse 11, 04315-Leipzig

Amtsgericht Düsseldorf: HRB 78227
Geschäftsführer: Martin Wimmer, Andreas Buchelt

www.modis.de

From: Dave Cramer <pg(at)fastcrypt(dot)com>
To: Pieter Zieschang <pieter(dot)zieschang(at)modis(dot)de>, List <
pgsql-jdbc(at)postgresql(dot)org>
Date: 29.06.2018 16:50
Subject: Re: insert function runs forever if connection is lost,
keeping the table locked
Sent by: davecramer(at)gmail(dot)com

So to be clear the application is completely dead ? There are no java
threads still alive ?

Dave Cramer

davec(at)postgresintl(dot)com
www.postgresintl.com

On 29 June 2018 at 10:48, Dave Cramer <pg(at)fastcrypt(dot)com> wrote:
I didn't intend not to reply to the list.

Dave Cramer

davec(at)postgresintl(dot)com
www.postgresintl.com

On 29 June 2018 at 10:46, Pieter Zieschang <pieter(dot)zieschang(at)modis(dot)de>
wrote:
Hi,

no, this is a plain JRE application which does connect via

Properties props = new Properties();
props.setProperty("user", user);
props.setProperty("password", pass);
conn = DriverManager.getConnection
("jdbc:postgresql://" + dbname, props);
conn.setAutoCommit(false);

conn.setTransactionIsolation(Connection.TRANSACTION_READ_COMMITTED);

_________________________________________

Pieter Zieschang

Modis IT Outsourcing GmbH
Kohlgartenstrasse 11, 04315-Leipzig

Amtsgericht Düsseldorf: HRB 78227
Geschäftsführer: Martin Wimmer, Andreas Buchelt

www.modis.de

From: Dave Cramer <pg(at)fastcrypt(dot)com>
To: Pieter Zieschang <pieter(dot)zieschang(at)modis(dot)de>
Date: 29.06.2018 16:37
Subject: Re: insert function runs forever if connection is lost,
keeping the table locked
Sent by: davecramer(at)gmail(dot)com

On 29 June 2018 at 10:27, Pieter Zieschang <pieter(dot)zieschang(at)modis(dot)de>
wrote:
Hi,

Thanks for your answer, unfortunately it didn't solve the problem.

I tried setting CallableStatement.setQueryTimeout(6).
This works, but causes the 2nd software run to die, because the deceased
first run did never release the lock.
Die dead application however keeps the lock waiting.

Is there any chance that you have a connection pool in the middle ?

Dave Cramer

davec(at)postgresintl(dot)com
www.postgresintl.com

From: Dave Cramer <pg(at)fastcrypt(dot)com>
To: Pieter Zieschang <pieter(dot)zieschang(at)modis(dot)de>
Date: 29.06.2018 14:58
Subject: Re: insert function runs forever if connection is lost,
keeping the table locked
Sent by: davecramer(at)gmail(dot)com

On 28 June 2018 at 09:27, Pieter Zieschang <pieter(dot)zieschang(at)modis(dot)de>
wrote:
Hi,

running pg-jdbc 42.2.2.jre7 against
PostgreSQL 10.4 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.8.5
20150623 (Red Hat 4.8.5-28), 64-bit

and using CallableStatement interface.
When the application crashes after cstmt.execute(), not closing or rolling
back anything the query stays active and keeps the table locked (the
function, uses in/out parameters and inserts to a table).
This would probably be the same if the client suddenly disconnects with a
open CallableStatement which was executed but not closed, committed or
rolled back.

The application in question is required to use CallableStatement.

I tried with settings
tcp_keepalives_idle
tcp_keepalives_interval
tcp_keepalives_count

all set to 2.

Doesn't help, the query is still listed as active and the table lock is
preventing other connections from doing anything for hours.

Is there any solution to this kind of deadlock caused by connection being
lost?
What i would expect to happen: The DB recognises the connection is gone
within 6 seconds and rolls back the transaction, thereby releasing the
lock.

That is exactly what I would expect to happen as well.

JDBC has a statement timeout setting. Have you tried that ?

What logs do you have from the server ?

Dave Cramer

davec(at)postgresintl(dot)com
www.postgresintl.com

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