Hi,
I'm using libhdfs C interface to access HDFS.
The application accessing HDFS has a master process that forks many
processes, and these processes try to connect to HDFS.
Upon connection, one of the processes is exiting as soon as it reaches the
hdfsConnect().
I tried simulating this behavior by creating a separate application where
the master process forks two processes that connect to HDFS and send
requests.. this worked without any problem.. so I got confused.. what's
really causing the connection problems then?
Any insights on this is much appreciated.

Hi Tareq,

This is because libhdfs will keep a bit of state data (especially if the master was connected to HDFS).

Three suggestions:
1) [Likely to work] Fork the children first, then do any HDFS actions in the master.  Alternately, don't have the master do any HDFS actions; have it fork a child which does them for it.
2) [May work] Try disconnecting the master from HDFS, then forking the children.
3) [If 2 doesn't work] Have the master disconnect, then fork the children, then have the children exec.

Brian

On Mar 22, 2012, at 11:38 PM, Tareq Aljabban wrote:

> Hi,
> I'm using libhdfs C interface to access HDFS.
> The application accessing HDFS has a master process that forks many
> processes, and these processes try to connect to HDFS.
> Upon connection, one of the processes is exiting as soon as it reaches the
> hdfsConnect().
> I tried simulating this behavior by creating a separate application where
> the master process forks two processes that connect to HDFS and send
> requests.. this worked without any problem.. so I got confused.. what's
> really causing the connection problems then?
> Any insights on this is much appreciated.

Hi Brian,
Thanks for your response..
Actually the master process doesn't even try to access HDFS..
What's happening is that process Master forks 2 processes A and B.
A and B are the ones that try to connect to HDFS..
I tried doing this in a separate application and it worked.. for some
reason it doesn't work in the other application that I'm working on.
Since I'm not connecting from master then I cannot really apply any of your
advices.. do you have other ideas?
Thanks

On Fri, Mar 23, 2012 at 7:25 AM, Brian Bockelman <[EMAIL PROTECTED]>wrote:

> Hi Tareq,
>
> This is because libhdfs will keep a bit of state data (especially if the
> master was connected to HDFS).
>
> Three suggestions:
> 1) [Likely to work] Fork the children first, then do any HDFS actions in
> the master.  Alternately, don't have the master do any HDFS actions; have
> it fork a child which does them for it.
> 2) [May work] Try disconnecting the master from HDFS, then forking the
> children.
> 3) [If 2 doesn't work] Have the master disconnect, then fork the children,
> then have the children exec.
>
> Brian
>
> On Mar 22, 2012, at 11:38 PM, Tareq Aljabban wrote:
>
> > Hi,
> > I'm using libhdfs C interface to access HDFS.
> > The application accessing HDFS has a master process that forks many
> > processes, and these processes try to connect to HDFS.
> > Upon connection, one of the processes is exiting as soon as it reaches
> the
> > hdfsConnect().
> > I tried simulating this behavior by creating a separate application where
> > the master process forks two processes that connect to HDFS and send
> > requests.. this worked without any problem.. so I got confused.. what's
> > really causing the connection problems then?
> > Any insights on this is much appreciated.
>
>

Hi Tareq,

Sorry - out of ideas, without doing something like "strace"ing the process to verify that the master never tries to initialize a JVM.

If exec'ing doesn't work, then it is certainly something in the environment.

Brian

On Mar 27, 2012, at 10:07 AM, Tareq Aljabban wrote:

> Hi Brian,
> Thanks for your response..
> Actually the master process doesn't even try to access HDFS..
> What's happening is that process Master forks 2 processes A and B.
> A and B are the ones that try to connect to HDFS..
> I tried doing this in a separate application and it worked.. for some reason it doesn't work in the other application that I'm working on.
> Since I'm not connecting from master then I cannot really apply any of your advices.. do you have other ideas?
> Thanks
>
> On Fri, Mar 23, 2012 at 7:25 AM, Brian Bockelman <[EMAIL PROTECTED]> wrote:
> Hi Tareq,
>
> This is because libhdfs will keep a bit of state data (especially if the master was connected to HDFS).
>
> Three suggestions:
> 1) [Likely to work] Fork the children first, then do any HDFS actions in the master.  Alternately, don't have the master do any HDFS actions; have it fork a child which does them for it.
> 2) [May work] Try disconnecting the master from HDFS, then forking the children.
> 3) [If 2 doesn't work] Have the master disconnect, then fork the children, then have the children exec.
>
> Brian
>
> On Mar 22, 2012, at 11:38 PM, Tareq Aljabban wrote:
>
> > Hi,
> > I'm using libhdfs C interface to access HDFS.
> > The application accessing HDFS has a master process that forks many
> > processes, and these processes try to connect to HDFS.
> > Upon connection, one of the processes is exiting as soon as it reaches the
> > hdfsConnect().
> > I tried simulating this behavior by creating a separate application where
> > the master process forks two processes that connect to HDFS and send
> > requests.. this worked without any problem.. so I got confused.. what's
> > really causing the connection problems then?
> > Any insights on this is much appreciated.
>
>