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Thread: No timeout to establish Connection?

No timeout to establish Connection?

From
"Roman Fail"
Date:
Please forgive my ignorance if this has already been covered, but the list archives are down.  (If anyone is
interested,the archive page returns: DB err: FATAL: No pg_hba.conf entry for host 64.117.224.193, user pgsql, database
186_archives).
 
Anyway, on to my problem.  I am using pg73jdbc3.jar (dated 11/30/2002) on a production Tomcat 4.1.24 Linux server.  The
PostgreSQLserver is a separate machine running 7.3.1, also on Linux.  (Of course I plan on upgrading to 7.3.3 and the
latestJDBC driver ASAP).
 
 
The symptom:
Tomcat would almost completely crash whenever the Postgres database was accessed.  While I did not have time to fully
quantifythe exact Java problem, it appears that the opening of a new Connection set caused the crash.  (Note, JVM did
notcrash, just all the webapps).  My guess is that the the DriverManager.getConnection(...) statement just runs and
runsbut never completes.  No timeout, so the whole JVM is waiting on it to finish.
 
 
My workaround is to create a separate thread to get the Connection, then call myThread.join(5000) so I only wait around
5seconds for the Connection.  If it didn't return a Connection by then, resume processing in the main thread and
abandonthat Thread.  Should I be concerned about a memory leak here and try to kill the thread somehow?
 
 
The cause:
The PostgreSQL server had a SCSI RAID backplane start to go bad, with lots of random disk errors.  The drives on the
badbackplane contained the OS and /usr/local/pgsql, but /usr/local/pgsql/data is on another backplane that was fine.
Theserver would generally boot fine and operate normally until a disk error occured.  At that point any Linux processes
thattried to access drives on the bad backplane would just hang.  The kernel still works since it's in memory, it will
acceptnew TCP connections, all daemons are still running.  Postgres itself still runs fine for existing connections,
sincethe postmaster was loaded in memory and the data drives were still accessible on the good backplane.  I presume
thatopening a new Connection would create a new pid, which the kernel would try to write to the bad drives....and hang.

 
 
The real question:
Is there a connection timeout in the JDBC driver?  Should there be?  This seems like a reasonable situation to provide
handlingfor.  
 
 
Thanks for listening to my problem!
 
Roman Fail
POS Portal, Inc.
916-563-1943

Re: No timeout to establish Connection?

From
"Roman Fail"
Date:
Scot:
That's a great suggestion, and one that I will definitely make use of in the future.  However, the hardware has now
beenreplaced and everything is working again.  It's not the kind of problem that I can think of a way to replicate, so
I'mstuck providing anecdotes and not hard facts. 
 
 
Thanks for your input!
 
Roman

    -----Original Message----- 
    From: Scot Floess [mailto:floesss@dstm.com] 
    Sent: Thu 7/3/2003 12:11 PM 
    To: Roman Fail; pgsql-jdbc@postgresql.org 
    Cc: 
    Subject: RE: [JDBC] No timeout to establish Connection?
    
    

    Roman:
    
    I really don't have an answer to this...but I would like to make a comment.
    You "think" that your code is stuck in DriverManager.getConnection().  To
    confirm, you can issue a kill -QUIT on the pid of the java process.  This
    will give you a thread dump of all threads...which will include what methods
    are currently executing.  If you do this twice over a period of time you
    might better see where the problem is...for instance it may not be
    DriverManager.getConnection().
    
    Again, I really don't have an answer but I find issuing the kill -QUIT <PID>
    to be very useful when debugging java problems...
    
    Scot
    
    -----Original Message-----
    From: Roman Fail [mailto:rfail@posportal.com]
    Sent: Thursday, July 03, 2003 2:40 PM
    To: pgsql-jdbc@postgresql.org
    Subject: [JDBC] No timeout to establish Connection?
    
    
    Please forgive my ignorance if this has already been covered, but the list
    archives are down.  (If anyone is interested, the archive page returns: DB
    err: FATAL: No pg_hba.conf entry for host 64.117.224.193, user pgsql,
    database 186_archives).
    
    Anyway, on to my problem.  I am using pg73jdbc3.jar (dated 11/30/2002) on a
    production Tomcat 4.1.24 Linux server.  The PostgreSQL server is a separate
    machine running 7.3.1, also on Linux.  (Of course I plan on upgrading to
    7.3.3 and the latest JDBC driver ASAP).
    
    The symptom:
    Tomcat would almost completely crash whenever the Postgres database was
    accessed.  While I did not have time to fully quantify the exact Java
    problem, it appears that the opening of a new Connection set caused the
    crash.  (Note, JVM did not crash, just all the webapps).  My guess is that
    the the DriverManager.getConnection(...) statement just runs and runs but
    never completes.  No timeout, so the whole JVM is waiting on it to finish.
    
    My workaround is to create a separate thread to get the Connection, then
    call myThread.join(5000) so I only wait around 5 seconds for the Connection.
    If it didn't return a Connection by then, resume processing in the main
    thread and abandon that Thread.  Should I be concerned about a memory leak
    here and try to kill the thread somehow?
    
    The cause:
    The PostgreSQL server had a SCSI RAID backplane start to go bad, with lots
    of random disk errors.  The drives on the bad backplane contained the OS and
    /usr/local/pgsql, but /usr/local/pgsql/data is on another backplane that was
    fine.  The server would generally boot fine and operate normally until a
    disk error occured.  At that point any Linux processes that tried to access
    drives on the bad backplane would just hang.  The kernel still works since
    it's in memory, it will accept new TCP connections, all daemons are still
    running.  Postgres itself still runs fine for existing connections, since
    the postmaster was loaded in memory and the data drives were still
    accessible on the good backplane.  I presume that opening a new Connection
    would create a new pid, which the kernel would try to write to the bad
    drives....and hang. 
    
    The real question:
    Is there a connection timeout in the JDBC driver?  Should there be?  This
    seems like a reasonable situation to provide handling for. 
    
    Thanks for listening to my problem!
    
    Roman Fail
    POS Portal, Inc.
    916-563-1943
    
    
    
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Re: No timeout to establish Connection?

From
Scot Floess
Date:
Roman:

I really don't have an answer to this...but I would like to make a comment.
You "think" that your code is stuck in DriverManager.getConnection().  To
confirm, you can issue a kill -QUIT on the pid of the java process.  This
will give you a thread dump of all threads...which will include what methods
are currently executing.  If you do this twice over a period of time you
might better see where the problem is...for instance it may not be
DriverManager.getConnection().

Again, I really don't have an answer but I find issuing the kill -QUIT <PID>
to be very useful when debugging java problems...

Scot

-----Original Message-----
From: Roman Fail [mailto:rfail@posportal.com]
Sent: Thursday, July 03, 2003 2:40 PM
To: pgsql-jdbc@postgresql.org
Subject: [JDBC] No timeout to establish Connection?


Please forgive my ignorance if this has already been covered, but the list
archives are down.  (If anyone is interested, the archive page returns: DB
err: FATAL: No pg_hba.conf entry for host 64.117.224.193, user pgsql,
database 186_archives).

Anyway, on to my problem.  I am using pg73jdbc3.jar (dated 11/30/2002) on a
production Tomcat 4.1.24 Linux server.  The PostgreSQL server is a separate
machine running 7.3.1, also on Linux.  (Of course I plan on upgrading to
7.3.3 and the latest JDBC driver ASAP).

The symptom:
Tomcat would almost completely crash whenever the Postgres database was
accessed.  While I did not have time to fully quantify the exact Java
problem, it appears that the opening of a new Connection set caused the
crash.  (Note, JVM did not crash, just all the webapps).  My guess is that
the the DriverManager.getConnection(...) statement just runs and runs but
never completes.  No timeout, so the whole JVM is waiting on it to finish.

My workaround is to create a separate thread to get the Connection, then
call myThread.join(5000) so I only wait around 5 seconds for the Connection.
If it didn't return a Connection by then, resume processing in the main
thread and abandon that Thread.  Should I be concerned about a memory leak
here and try to kill the thread somehow?

The cause:
The PostgreSQL server had a SCSI RAID backplane start to go bad, with lots
of random disk errors.  The drives on the bad backplane contained the OS and
/usr/local/pgsql, but /usr/local/pgsql/data is on another backplane that was
fine.  The server would generally boot fine and operate normally until a
disk error occured.  At that point any Linux processes that tried to access
drives on the bad backplane would just hang.  The kernel still works since
it's in memory, it will accept new TCP connections, all daemons are still
running.  Postgres itself still runs fine for existing connections, since
the postmaster was loaded in memory and the data drives were still
accessible on the good backplane.  I presume that opening a new Connection
would create a new pid, which the kernel would try to write to the bad
drives....and hang.

The real question:
Is there a connection timeout in the JDBC driver?  Should there be?  This
seems like a reasonable situation to provide handling for.

Thanks for listening to my problem!

Roman Fail
POS Portal, Inc.
916-563-1943



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