Joey, here is the information: Cluster Summary (Heap Size is 481.88 MB/1.74
GB)Maps Reduces Total Submissions Nodes Map Task Capacity Reduce Task Capacity
Avg. Tasks/Node Blacklisted Nodes
0 6 11 3 42
42 28.00 0
CheersRamon
Subject: Re: Why most of the free reduce slots are NOT used for my Hadoop
Jobs? Thanks.
From: j...@cloudera.com
Date: Sat, 10 Mar 2012 07:00:26 -0500
To: mapreduce-user@hadoop.apache.org
What does the jobtracker web page say is the total reduce capacity?
-Joey
On Mar 10, 2012, at 5:39, WangRamon <ramon_w...@hotmail.com> wrote:
Hi All
I'm using Hadoop-0.20-append, the cluster contains 3 nodes, for each node I
have 14 map and 14 reduce slots, here is the configuration:
<property>
<name>mapred.tasktracker.map.tasks.maximum</name>
<value>14</value>
</property>
<property>
<name>mapred.tasktracker.reduce.tasks.maximum</name>
<value>14</value>
</property>
<property>
<name>mapred.reduce.tasks</name>
<value>73</value>
</property>
When I submit 5 Jobs simultane
ously (the input data for each job is not so big for the test, it's about 2~5M
in size), I assume the Jobs will use the slots as much as possible, each Job
did created 73 Reduce Tasks as configured above, so there will be 5 * 73 Reduce
Tasks in total, but, most of them are in pending state, only about 12 of them
are running, it's too small compared to the total slots number for reduce, 42
reduce slots for the 3 nodes cluster.
What interestring is that it always about 12 of them are running, I tried a few
times.
So, I thought it might because about the scheduler, I changed it to Fair
Scheduler, I created 3 pools, the configure is as below:
<?xml version="1.0"?>
<allocations>
<pool name="pool-a">
<minMaps>14</minMaps>
<minReduces>14</minReduces>
<weight>1.0</weight>
</pool>
<pool name="pool
-b">
<minMaps>14</minMaps>
<minReduces>14</minReduces>
<weight>1.0</weight>
</pool>
<pool name="pool-c">
<minMaps>14</minMaps>
<minReduces>14</minReduces>
<weight>1.0</weight>
</pool>
</allocations>
Then I submit the 5 Jobs simultaneously to these pools randomly again, I can
see the jobs were assigned to different pools, but, it's still the same problem
only about 12 of the reduce tasks from different pool are running, here is the
output i copied from the Fair Scheduler monitor GUI:
pool-a 2 14 14 0 9
pool-b 0 14 14 0 0
pool-c 2 14 14 0 3
pool-a and pool-c have a total of 12 reduce tasks running, but I do have about
11 reduce slots at least available in my cluster.
So can anyone
please give me some suggestions, why NOT all my REDUCE SLOTS are working?
Thanks in advance.
Cheers
Ramon
