Re: ls performance on directories with small number of items

[Aaron Roberts <aroberts@xxxxxxxxxxxxxx>]

Thanks Sam/Julian,

               I understand roughly, that readir() and others are simply hard to solve with a distributed filesystem and that NFS can do this part faster.  I’d like to see if gluster can be tweaked a bit to get this working.

 

performance.stat-prefetch is set to ‘on’.

 

Would performance.md-cache-timeout help me?

It is set to 1 on my volume (default).  Would raising this help with servicing large number of hits for a single file/dir?

 

Thanks,

               Aaron

 

From: Joe Julian [mailto:joe@xxxxxxxxxxxxxxxx]
Sent: 27 November 2017 23:45
To: gluster-users@xxxxxxxxxxx; Sam McLeod <mailinglists@xxxxxxxxxxx>; Aaron Roberts <aroberts@xxxxxxxxxxxxxx>
Cc: gluster-users@xxxxxxxxxxx
Subject: Re: [Gluster-users] ls performance on directories with small number of items

 

Also note, Sam's example is comparing apples and orchards. Feeding one person from an orchard is not as efficient as feeding one person an apple, but if you're feeding 10000 people...

Also in question with the NFS example, how long until that chown was flushed? How long until another client could see those changes? That is ignoring the biggie, what happens when the NFS server goes down?

On November 27, 2017 2:49:23 PM PST, Sam McLeod <mailinglists@xxxxxxxxxxx> wrote:

Hi Aaron,

 

We also find that Gluster is perhaps, not the most performant when performing actions on directories containing large numbers of files.

For example, with a single NFS server on the client side a recursive chown on (many!) files took about 18 seconds, our simple two replica gluster servers took over 15 minutes.

Having said that, while I'm new to the gluster world, things seem to be progressing quite quickly in regards to attempts to improve performance.

 

I noticed you're running a _very_ old version of Gluster, I'd first suggest upgrading to the latest stable (3.12.x) and FYI 3.13 is to be release shortly.

 

I'd also recommend ensuring the following setting is enabled:

 

performance.stat-prefetch

 

Further to this, additional information about the cluster / volume typology and configuration would help others assist you (but I still think you should upgrade!).

--
Sam McLeod
https://smcleod.net
https://twitter.com/s_mcleod

On 28 Nov 2017, at 12:18 am, Aaron Roberts <aroberts@xxxxxxxxxxxxxx> wrote:

 

Hi,

               I have a situation where an apache web server is trying to locate the IndexDocument for a directory on a gluster volume.  This URL is being hit roughly 20 times per second.  There is only 1 file in this directory.  However, the parent directory does have a large number of items (+123,000 files and dirs) and we are performing operations to move these files into 2 levels of subdirs.

 

We are seeing very slow response times (around 8 seconds) in apache and also when trying to ls on this dir.  Before we started the migrations to move files on the large parent dir into 2 sub levels, we weren’t aware of a problem.

 

[root@web-02 images]# time ls -l dir1/get/ | wc -l

2

 

real    0m8.114s

user    0m0.002s

sys     0m0.014s

 

Other directories with only 1 item return very quickly (<1 sec).

 

[root@Web-01 images]# time ls -l dir1/tmp1/ | wc -l

2

 

real    0m0.014s

user    0m0.003s

sys     0m0.006s

 

I’m just trying to understand what would slow down this operation so much.  Is it the high frequency of attempts to read the directory (apache hits to dir1/get/) ?  Do the move operations on items in the parent directory have any impact?

 

Some background info:

 

[root@web-02 images]# gluster --version

glusterfs 3.7.20 built on Jan 30 2017 15:39:29

Repository revision: git://git.gluster.com/glusterfs.git

Copyright (c) 2006-2011 Gluster Inc. <http://www.gluster.com>

GlusterFS comes with ABSOLUTELY NO WARRANTY.

You may redistribute copies of GlusterFS under the terms of the GNU General Public License.

 

[root@web-02 images]# gluster vol info

 

Volume Name: web_vol1

Type: Replicate

Volume ID: 0d63de20-c9c2-4931-b4a3-6aed5ae28057

Status: Started

Number of Bricks: 1 x 2 = 2

Transport-type: tcp

Bricks:

Brick1: web-01:/export/brick1/web_vol1_brick1

Brick2: web-02:/export/brick1/web_vol1_brick1

Options Reconfigured:

performance.readdir-ahead: on

performance.io-thread-count: 32

performance.cache-size: 512MB

 

 

Any insight would be gratefully received.

 

Thanks,

               Aaron

 

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