[Bugs] [Bug 1377193] New: Poor smallfile read performance on Arbiter volume compared to Replica 3 volume

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1377193

            Bug ID: 1377193
           Summary: Poor smallfile read performance on Arbiter volume
                    compared to Replica 3 volume
           Product: GlusterFS
           Version: 3.8
         Component: arbiter
          Assignee: bugs at gluster.org
          Reporter: shberry at redhat.com
                CC: bugs at gluster.org



Description of problem:

Expectation was smallfile read performance on Arbiter volume would match
replica 3 smallfile read performance.
Observation is Arbiter volume read performance is 30% of replica 3 read
performance.

Version-Release number of selected component (if applicable):

glusterfs-cli-3.8.2-1.el7.x86_64
glusterfs-3.8.2-1.el7.x86_64
glusterfs-api-3.8.2-1.el7.x86_64
glusterfs-libs-3.8.2-1.el7.x86_64
glusterfs-fuse-3.8.2-1.el7.x86_64
glusterfs-client-xlators-3.8.2-1.el7.x86_64
glusterfs-server-3.8.2-1.el7.x86_64


How reproducible:

Every time.

gluster v info (Replica 3 volume)

Volume Name: rep3
Type: Distributed-Replicate
Volume ID: e7a5d84d-31da-40a8-85d0-2b94b95c3b28
Status: Started
Number of Bricks: 2 x 3 = 6
Transport-type: tcp
Bricks:
Brick1: 172.17.40.13:/bricks/b/g
Brick2: 172.17.40.14:/bricks/b/g
Brick3: 172.17.40.15:/bricks/b/g
Brick4: 172.17.40.16:/bricks/b/g
Brick5: 172.17.40.22:/bricks/b/g
Brick6: 172.17.40.24:/bricks/b/g
Options Reconfigured:
server.event-threads: 4
client.event-threads: 4
cluster.lookup-optimize: on
performance.readdir-ahead: on

gluster v info (Arbiter Volume)

Volume Name: arb
Type: Distributed-Replicate
Volume ID: e7a5d84d-31da-40a8-85d0-2b94b95c3b28
Status: Started
Number of Bricks: 3 x (2 + 1) = 9
Transport-type: tcp
Brick1: 172.17.40.13:/bricks/b01/g
Brick2: 172.17.40.14:/bricks/b01/g
Brick3: 172.17.40.15:/bricks/b02/g (arbiter)
Brick4: 172.17.40.15:/bricks/b01/g
Brick5: 172.17.40.16:/bricks/b01/g
Brick6: 172.17.40.22:/bricks/b02/g (arbiter)
Brick7: 172.17.40.22:/bricks/b01/g
Brick8: 172.17.40.24:/bricks/b01/g
Brick9: 172.17.40.13:/bricks/b02/g (arbiter)
Options Reconfigured:
server.event-threads: 4
client.event-threads: 4
cluster.lookup-optimize: on
performance.readdir-ahead: on


Steps to Reproduce:

For both Replica 3 volume and Arbiter Volume, do the following

1. Creation of files. Drop cache on server and client side. Create smallfile
files using command /root/smallfile/smallfile_cli.py --top /mnt/glusterfs
--host-set clientfile --threads 4 --file-size 256 --files 6554 --record-size 32
--fsync Y --operation create

2. Reading of files. Again drop cache on server and client side. Read
smallfiles using command /root/smallfile/smallfile_cli.py --top /mnt/glusterfs
--host-set clientfile --threads 4 --file-size 256 --files 6554  --record-size
32 --operation read

3. Compare the read performance for both replica 3 and Arbiter volume 

Actual results:

Arbiter read performance is 30% of replica 3 read performance for smallfile
workload.

Expected results:

Smallfile read performance of Arbiter volume and Replica 3 volume should
ideally be same.

--Shekhar

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