[
https://issues.apache.org/jira/browse/HADOOP-7714?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13119448#comment-13119448
]
Robert Joseph Evans commented on HADOOP-7714:
---------------------------------------------
Why is the change across the entire datanode? And why are we trying to guess
the usage pattern of the data based off of a hard coded read size of 256k?
It seems to me that there are other HDFS use cases that are not random reads of
< 256K, like the distributed cache or who knows what in the future with MRV2
where we want to keep the data cached in memory on the data node if possible.
I would much rather see an optional parameter to the open API for flags like
O_DIRECT. Then when HDFS talks to the data node it can also pass that
information off to it when initiating a block read. That way the application
can indicate how it expects to use the data. MAPREDCUE can say this is a
streaming read where we will probably never reread the data again and it can
also say this is reading a file from the distributed cache and 900 others are
going to read this same file so keep it in memory if possible.
> Add support in native libs for OS buffer cache management
> ---------------------------------------------------------
>
> Key: HADOOP-7714
> URL: https://issues.apache.org/jira/browse/HADOOP-7714
> Project: Hadoop Common
> Issue Type: Bug
> Components: native
> Affects Versions: 0.24.0
> Reporter: Todd Lipcon
> Assignee: Todd Lipcon
> Attachments: hadoop-7714-20s-prelim.txt
>
>
> Especially in shared HBase/MR situations, management of the OS buffer cache
> is important. Currently, running a big MR job will evict all of HBase's hot
> data from cache, causing HBase performance to really suffer. However, caching
> of the MR input/output is rarely useful, since the datasets tend to be larger
> than cache and not re-read often enough that the cache is used. Having access
> to the native calls {{posix_fadvise}} and {{sync_data_range}} on platforms
> where they are supported would allow us to do a better job of managing this
> cache.
--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators:
https://issues.apache.org/jira/secure/ContactAdministrators!default.jspa
For more information on JIRA, see: http://www.atlassian.com/software/jira
