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From "Rohini Palaniswamy (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-5785) Derive task attempt JVM max heap size and io.sort.mb automatically from mapreduce.*.memory.mb
Date Mon, 14 Jul 2014 17:44:05 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-5785?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14060919#comment-14060919
] 

Rohini Palaniswamy commented on MAPREDUCE-5785:
-----------------------------------------------

I was taking a look at https://issues.apache.org/jira/browse/MAPREDUCE-5785 and https://issues.apache.org/jira/browse/TEZ-699
. 
 
MR:
{code}
public static final float DEFAULT_MEMORY_MB_HEAP_RATIO = 1.33f;
float heapRatio = conf.getFloat(MRJobConfig.MEMORY_MB_HEAP_RATIO,
          MRJobConfig.DEFAULT_MEMORY_MB_HEAP_RATIO);
int taskHeapSize =(int)Math.ceil(taskContainerMb / heapRatio);
public static final float DEFAULT_IO_SORT_MB_HEAP_RATIO = 0.5f;
ioSortMbPer = JobContext.DEFAULT_IO_SORT_MB_HEAP_RATIO;
+        }
+        sortmb = (int)(maxHeapMb * ioSortMbPer);
{code}
Tez:
{code}
public static final String TEZ_CONTAINER_MAX_JAVA_HEAP_FRACTION =
+      TEZ_PREFIX + "container.max.java.heap.fraction";
+  public static final double TEZ_CONTAINER_MAX_JAVA_HEAP_FRACTION_DEFAULT = 0.8;
int maxMemory = (int)(resource.getMemory() * maxHeapFactor);
 {code}

Few issues, inconsistencies that I see:
  - The MR one is really confusing. For heap it is divide by and io.sort.mb it is multiplication.
I think it would be easier to keep both same to avoid confusion.  I had to apply more of my
grey cells to do the division. Would prefer multiplication to determine the percentage as
it is more easy to compute in mind than division.
   -  io.sort.mb as 50% of heap seems too high for default value. Most of the pig jobs which
have huge bags would start failing.
- Another issue is taking the defaults now, for a 
4G container – Tez Xmx = 3.2G, MR Xmx=3.0G
8G container – Tez Xmx = 6.2G, MR xmx = 6G. 
Though the defaults work well for 1 or 2G of memory, for higher memories they seem to be actually
wasting a lot of memory considering not more than 500M is usually required for native memory
even if the Xmx keeps increasing. We should account that factor into calculation instead of
doing Xmx as just a direct percentage of resource.mb.

Tez settings are usually equivalent of MR settings with an internal mapping to the MR setting
taking them if they are specified, so that it is easier for users to switch between frameworks.
This is one thing I am seeing inconsistent in terms of how the value is specified and would
be good to reconcile both to have same behavior.

> Derive task attempt JVM max heap size and io.sort.mb automatically from mapreduce.*.memory.mb
> ---------------------------------------------------------------------------------------------
>
>                 Key: MAPREDUCE-5785
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-5785
>             Project: Hadoop Map/Reduce
>          Issue Type: New Feature
>          Components: mr-am, task
>            Reporter: Gera Shegalov
>            Assignee: Gera Shegalov
>         Attachments: MAPREDUCE-5785.v01.patch, MAPREDUCE-5785.v02.patch, MAPREDUCE-5785.v03.patch
>
>
> Currently users have to set 2 memory-related configs per Job / per task type.  One first
chooses some container size map reduce.\*.memory.mb and then a corresponding maximum Java
heap size Xmx < map reduce.\*.memory.mb. This makes sure that the JVM's C-heap (native
memory + Java heap) does not exceed this mapreduce.*.memory.mb. If one forgets to tune Xmx,
MR-AM might be 
> - allocating big containers whereas the JVM will only use the default -Xmx200m.
> - allocating small containers that will OOM because Xmx is too high.
> With this JIRA, we propose to set Xmx automatically based on an empirical ratio that
can be adjusted. Xmx is not changed automatically if provided by the user.



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