CM enforces max locked memory on datanode process

[#1]

Hello,

When setting the parameter "dfs.datanode.max.locked.memory" to a value other than 0, it is supposed to be the user's responsibility to set the MEMLOCK limits accordingly. CM does not leave that for the user and enforces it. (as seen on /proc/<pid>/limits)

This parameter is used by HDFS only to limt cache resources, so there is no real reason for CM to enforce this limit on an OS level. By doing so, CM does not allow external libraries (non-cache related) on the datanode to allocate memory past this limit. 

To make a long story short, I'd like to cancel CM's enforcement of this limit and set the limits myself. Is there any way I could do so?

Thanks,

Elad

[#2 · Accepted solution]

Hi Elad,

You can set probably dfs.datanode.max.locked.memory to the value you want to enforced by the OS, then use the Advanced Configuration Snippet for hdfs-site.xml to change the value that HDFS actually sees for this parameter in hdfs-site.

If CM didn't set memlock, then HDFS caching would be at the mercy of the default memlock setting and could fail unexpectedly, with essentially no workaround. So it's pretty important that CM sets this limit to something that will make caching work.

Thanks,
Darren

[#3]

Thanks a lot Darren, a very simple solution 🙂