[
https://issues.apache.org/jira/browse/HADOOP-13065?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15270485#comment-15270485
]
Steve Loughran commented on HADOOP-13065:
-----------------------------------------
ALong has contention under load; it doesn't compile down to a simple x86 {{LOCK
XADD $address, value}}, which is all you need. The updater stuff is designed to
get closer to this with something eventually generated code like
{code}
address = &object + offset-to-field
LOCK XADD $address, value
{code}
(no, I can't code x86 ASM. I just spent lots of time staring at it trying to
debug windows C++ code)
The Java 9 stuff is actually intended to something really profound: provide the
same operations against arrays, so {{address = array + (aligned) offset}}, C's
*(array+offset) ++ were the type of array some atomic long[].
The fencing stuff is just there to make people who think they understand memory
models, CPU and compiler re-ordering & the like write fast code. I've only ever
seen anyone argue for doing that in user level code once [Twitter: eventually
consistent data structures|https://vimeo.com/43903960] and their code only
worked because they didn't understand that in Java 5+, volatile reads are
non-reorderable fences on all accesses. (that is: he gets the explanation of
why things work wrong). Nobody should be going near that in the Hadoop code at
all.
> Add a new interface for retrieving FS and FC Statistics
> -------------------------------------------------------
>
> Key: HADOOP-13065
> URL: https://issues.apache.org/jira/browse/HADOOP-13065
> Project: Hadoop Common
> Issue Type: Improvement
> Components: fs
> Reporter: Ram Venkatesh
> Assignee: Mingliang Liu
> Attachments: HADOOP-13065-007.patch, HADOOP-13065.008.patch,
> HDFS-10175.000.patch, HDFS-10175.001.patch, HDFS-10175.002.patch,
> HDFS-10175.003.patch, HDFS-10175.004.patch, HDFS-10175.005.patch,
> HDFS-10175.006.patch, TestStatisticsOverhead.java
>
>
> Currently FileSystem.Statistics exposes the following statistics:
> BytesRead
> BytesWritten
> ReadOps
> LargeReadOps
> WriteOps
> These are in-turn exposed as job counters by MapReduce and other frameworks.
> There is logic within DfsClient to map operations to these counters that can
> be confusing, for instance, mkdirs counts as a writeOp.
> Proposed enhancement:
> Add a statistic for each DfsClient operation including create, append,
> createSymlink, delete, exists, mkdirs, rename and expose them as new
> properties on the Statistics object. The operation-specific counters can be
> used for analyzing the load imposed by a particular job on HDFS.
> For example, we can use them to identify jobs that end up creating a large
> number of files.
> Once this information is available in the Statistics object, the app
> frameworks like MapReduce can expose them as additional counters to be
> aggregated and recorded as part of job summary.
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
