Thanks for the clarification Guyla,
I had 9 slots per node, however one node only has 3 CPUs.So, my parallelism
here was 9, and all tasks were allocated to the 9 slots on the one host
I understand the strategy of trying to minimize network IOs by sending to the
same host, but in this case where the number of slots exceeds the number of
CPUs, the strategy seems to fail to distribute the load across the 9
'available' CPUs.
My thinking is having more than 1 slots per CPU is that my tasks are not
homogeneous, so one task may receive data, while another is waiting for more
data. So I may have many jobs running, with only some being actually used
because the data determines what job is being used. In that case, ideally I
want the working jobs distributed accross available CPUs, not available slots
on the closest host.Is there a way to achieve that?
Date: Thu, 12 Mar 2015 20:28:29 +0100
Subject: Re: Flink logs only written to one host
From: gyf...@apache.org
To: user@flink.apache.org
Hey,
Let me clarify some things regarding distribute(). You should only specify a
partitioning scheme like distribute or shuffle or groupby in cases when it
actually matters for you how the data is partitioned across operator instances.
By default forwarding is applied which works in the following way:
When the output parallelism (source in this case) is the same as the receiver
parallelism (map) the data is forwarded to the task that is on the same task
manager which reduces network costs. This also allows chaining of subtasks
which fully eliminates the serialization costs.
When the output parallelism is smaller or larger (in your case 1 as the socket
is non parallel) it applies a round robin scheme, same as distribute.
So in your case you dont have to call distribute you will get the same result
without it.
Cheers,Gyula
On Thu, Mar 12, 2015 at 8:17 PM, Emmanuel <ele...@msn.com> wrote:
Hi,
I did change my config to have parallelism of 9 and 3 slots on each machine and
now it does distribute properly.
The other day I was told i could have many more slots than CPUs available and
the system would distribute the load properly between the hosts with available
CPU time, but it doesn't seem to be the case here:with 9 slots on each hosts,
the distribute partitioning still send all 9 tasks to the 9 slots on the same
machine even though it only has 3CPUs available and the other 6 CPUs on the
other machines were not running anything.
The idea of having more slots than CPUs to me is that you can spin out more
jobs and they'll be balanced as data comes... but with few jobs it seems odd
that the task are all attributed to the same host just because it has slots
available.
Anyways, that fixed that issue for me for now.. .looking forward to learning
more about Flink
Date: Thu, 12 Mar 2015 20:00:32 +0100
Subject: RE: Flink logs only written to one host
From: fhue...@gmail.com
To: user@flink.apache.org
Can you check the JM log file how many slots are available?
Slots are configured per TM. If you configure 9 slots and 3 TMs you end up with
27 slots, 9 on each TM.
On Mar 12, 2015 7:55 PM, "Emmanuel" <ele...@msn.com> wrote:
It appears actually that the slots used are all on the same host.My guess is
because I am using the default partitioning method (forward, which defaults to
the same host)
However I now tried .shuffle() and .distribute() without any luck:
I have a DataStream<String> text = env.socketTextStream(inHostName, inPort);
this is the one socket input stream.Adding text.distribute().map(...)does not
seem to distribute the .map() process on the other hosts.Is this the correct
way to use .distribute() on a stream input? ThanksEmmanuel
From: ele...@msn.com
To: user@flink.apache.org
Subject: Flink logs only written to one host
Date: Thu, 12 Mar 2015 17:30:28 +0000
Hello,
I'm using a 3 nodes (3VMs) cluster, 3CPUs each, parallelism of 9, I usually
only see taskmanager.out logs generated only on one of the 3 nodes when I use
the System.out.println() method, to print debug info in my main processing
function.
Is this expected? Or am I just doing something wrong? I stream from a socket
with socketTextStream; I understand that this job runs on a single process, and
I see that in the UI (using one slot only), but the computation task runs on 9
slots. That task includes the System.out.println() statement, yet it only shows
on one host's .out log folder. The host is not always the same, so I have to
tail all logs on all hosts, but I'm surprised of this behavior.Am I just
missing something? Are 'print' statement to stdout aggregated on one host
somehow? If so how is this controlled? Why would that host change?
I would love to understand what is going on, and if maybe somehow the 9 slots
may be running on a single host which would defeat the purpose.
Thanks for the insight
Emmanuel
