[Bugs] [Bug 1215385] New: rmtab file is a bottleneck when lot of clients are accessing a volume through NFS

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1215385

            Bug ID: 1215385
           Summary: rmtab file is a bottleneck when lot of clients are
                    accessing a volume through NFS
           Product: GlusterFS
           Version: 3.7.0
         Component: nfs
          Keywords: Triaged
          Severity: urgent
          Assignee: ndevos at redhat.com
          Reporter: ndevos at redhat.com
                CC: bugs at gluster.org, gluster-bugs at redhat.com
        Depends On: 1169317
            Blocks: 1199352 (glusterfs-3.7.0)



+++ This bug was initially created as a clone of Bug #1169317 +++

+++ This bug was initially created as a clone of Bug #1166862 +++

Description of problem:

This feature: http://review.gluster.org/#/c/4430/

Create bottleneck when several clients are accessing a nfs volume.

On our setup:

Gluster 3.5.2 under centos7.

Hardware:

    dual Xeon® CPU E5-2640
    64GB RAM
    SSD for rootfs
    10Gb NIC

Context:

    Around 700 nfs clients for small file or vm images.


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

3.5.2

How reproducible:

Always as long as you have enough NFS clients

Steps to Reproduce:
1. Create a volume accessible through gluster nfs
2. Make it accessible for 700 clients
3. See how it hangs

Actual results:

NFS client got intermittent hang (every minutes / for 10s each time). Even an
“rpcinfo -t server nfs 3" will hang.

Gluster nfs process literally eat the CPU of the server

Expected results:

No hanging

Additional info:

The cause:

the rmtab file located in /var/lib/glusterd/nfs/ is flushed from memory to 
/var/lib/glusterd/nfs/rmtab.tmp. During this time, NFS server hang literraly.

Workaroud:

Move the file to memory for faster I/O using this option:

set nfs.mount-rmtab: /dev/shm/glusterfs.rmtab

Result:

We still have some hang but for ~300ms now, the load average of the server is
WAY better.

Personal thought:

This feature is not usable and should be disabled by default.

You can find attached load average and Disk usage before and after using SHM
for rmtab.

--- Additional comment from Anand Avati on 2014-12-01 11:32:14 CET ---

REVIEW: http://review.gluster.org/9223 (nfs: make it possible to disable
nfs.mount-rmtab) posted (#2) for review on master by Niels de Vos
(ndevos at redhat.com)

--- Additional comment from Anand Avati on 2014-12-01 15:18:03 CET ---

REVIEW: http://review.gluster.org/9223 (nfs: make it possible to disable
nfs.mount-rmtab) posted (#4) for review on master by Niels de Vos
(ndevos at redhat.com)

--- Additional comment from Anand Avati on 2014-12-02 12:14:50 CET ---

REVIEW: http://review.gluster.org/9223 (nfs: make it possible to disable
nfs.mount-rmtab) posted (#5) for review on master by Niels de Vos
(ndevos at redhat.com)

--- Additional comment from Anand Avati on 2014-12-05 22:30:27 CET ---

REVIEW: http://review.gluster.org/9223 (nfs: make it possible to disable
nfs.mount-rmtab) posted (#6) for review on master by Niels de Vos
(ndevos at redhat.com)

--- Additional comment from Anand Avati on 2015-04-26 10:40:25 CEST ---

COMMIT: http://review.gluster.org/9223 committed in master by Niels de Vos
(ndevos at redhat.com) 
------
commit 331ef6e1a86bfc0a93f8a9dec6ad35c417873849
Author: Niels de Vos <ndevos at redhat.com>
Date:   Tue Dec 2 10:54:53 2014 +0100

    nfs: make it possible to disable nfs.mount-rmtab

    When there are many NFS-clients doing very often mount/unmount actions,
    the updating of the 'rmtab' can become a bottleneck and cause delays. In
    these situations, the output of 'showmount' may be less important than
    the responsiveness of the (un)mounting.

    By setting 'nfs.mount-rmtab' to the value "/-", the cache file is not
    updated anymore, and the entries are only kept in memory.

    BUG: 1169317
    Change-Id: I40c4d8d754932f86fb2b1b2588843390464c773d
    Reported-by: Cyril Peponnet <cyril at peponnet.fr>
    Signed-off-by: Niels de Vos <ndevos at redhat.com>
    Reviewed-on: http://review.gluster.org/9223
    Tested-by: Gluster Build System <jenkins at build.gluster.com>
    Reviewed-by: soumya k <skoduri at redhat.com>
    Reviewed-by: jiffin tony Thottan <jthottan at redhat.com>
    Reviewed-by: Kaleb KEITHLEY <kkeithle at redhat.com>


Referenced Bugs:

https://bugzilla.redhat.com/show_bug.cgi?id=1169317
[Bug 1169317] rmtab file is a bottleneck when lot of clients are accessing
a volume through NFS
https://bugzilla.redhat.com/show_bug.cgi?id=1199352
[Bug 1199352] GlusterFS 3.7.0 tracker
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