[Bugs] [Bug 1271310] New: RFE : Feature: Tunable FOP sampling for v3.6.x/v3.7.x

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1271310

            Bug ID: 1271310
           Summary: RFE : Feature: Tunable FOP sampling for v3.6.x/v3.7.x
           Product: GlusterFS
           Version: mainline
         Component: core
          Keywords: FutureFeature, Triaged
          Severity: medium
          Priority: medium
          Assignee: bugs at gluster.org
          Reporter: jdarcy at redhat.com
                CC: bugs at gluster.org, gluster-bugs at redhat.com,
                    rwareing at fb.com, sshreyas at fb.com
        Depends On: 1262092



Cloning for master.

+++ This bug was initially created as a clone of Bug #1262092 +++

Description of problem:

debug/io-stats: FOP sampling feature

- Using sampling feature you can record details about every Nth FOP.
  The fields in each sample are: FOP type, hostname, uid, gid, FOP priority,
  port and time taken (latency) to fufill the request.
- Implemented using a ring buffer which is not (m/c) allocated in the IO path,
  this should make the sampling process pretty cheap.
- DNS resolution done @ dump time not @ sample time for performance w/
  cache
- Metrics can be used for both diagnostics, traffic/IO profiling as well
  as P95/P99 calculations
- To control this feature there are two new volume options:
  diagnostics.fop-sample-interval - The sampling interval, e.g. 1 means
  sample every FOP, 100 means sample every 100th FOP
  diagnostics.fop-sample-buf-size - The size (in bytes) of the ring
  buffer used to store the samples.  In the even more samples
  are collected in the stats dump interval than can be held in this buffer,
  the oldest samples shall be discarded.  Samples are stored in the log
  directory under /var/log/glusterfs/samples.
- Uses DNS cache written by sshreyas at fb.com (Thank-you!), the DNS cache
  TTL is controlled by the diagnostics.stats-dnscache-ttl-sec option
  and defaults to 24hrs.

Pre-requisite: Requires stats dump patch from bug 1261700 to function.

Version-Release number of selected component (if applicable):
3.6.x, 3.7.x

How reproducible:
100%

Steps to Reproduce:
n/a

Actual results:
n/a

Expected results:
n/a

Additional info:
n/a

--- Additional comment from Vijay Bellur on 2015-10-09 14:17:24 EDT ---

REVIEW: http://review.gluster.org/12210 (debug/io-stats: Add FOP sampling
feature) posted (#3) for review on master by Vijay Bellur (vbellur at redhat.com)


Referenced Bugs:

https://bugzilla.redhat.com/show_bug.cgi?id=1262092
[Bug 1262092] RFE : Feature: Tunable FOP sampling for v3.6.x/v3.7.x
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