Home | About | Sematext search-lucene.com search-hadoop.com
 Search Hadoop and all its subprojects:

Switch to Threaded View
MapReduce >> mail # user >> Large static structures in M/R heap

Copy link to this message
Re: Large static structures in M/R heap
Have you looked at things like CDB http://cr.yp.to/cdb.html that would
allow you to keep most of the file on disk and cache hot parts in memory.
That really depends on your access pattern.

Alternatively you could give yourself more heap and take up two slots for
your map task.

Also if it is big enough you might want to look at using a reduce to do
the join instead of trying to do a map side join.


On 2/27/13 12:42 PM, "Adam Phelps" <[EMAIL PROTECTED]> wrote:

>We have a job that uses a large lookup structure that gets created as a
>static class during the map setup phase (and we have the JVM reused so
>this only takes place once).  However of late this structure has grown
>drastically (due to items beyond our control) and we've seen a
>substantial increase in map time due to the lower available memory.
>Are there any easy solutions to this sort of problem?  My first thought
>was to see if it was possible to have all tasks for a job execute in
>parallel within the same JVM, but I'm not seeing any setting that would
>allow that.  Beyond that my only ideas are to move that data into an
>external one-per-node key-value store like memcached, but I'm worried
>the additional overhead of sending a query for each value being mapped
>would also kill the job performance.
>- Adam