[Gluster-users] ls performance on directories with small number of items

[Aaron Roberts]

Thanks Joe,
               Just to clarify, I’m seeing 8 seconds to run ls -l in a dir containing 2 files.  I mentioned that the _parent_ dir contains 123k items, in case it was relevant.  Although it seems that the fact we are hitting the dir with many requests seems to be the key factor.

Aaron


From: Joe Julian [mailto:joe at julianfamily.org]
Sent: 29 November 2017 16:16
To: gluster-users at gluster.org; Aaron Roberts <aroberts at domicilium.com>; gluster-users at gluster.org
Subject: Re: [Gluster-users] ls performance on directories with small number of items

The -l flag is causing a metadata lookup for every file in the directory. The way the ls command does that it's with individual fstat calls to each directory entry. That's a lot of tiny network round trips with fops that don't even fill a standard frame thus each frame has a high percentage of overhead for tcp. Add to that the replica check to ensure you're not getting stale data and you have another round trip for each file. Your 123k directory entries require several frames of getdirent and over 492k frames for the individual fstat calls. That's roughly 16us per frame.

Can you eliminate the fstat calls? If you only get the directory listing that should be significantly better. To prove this, do "echo *". You will instantly see your 123k entries.
On November 27, 2017 5:18:56 AM PST, Aaron Roberts <aroberts at domicilium.com<mailto:aroberts at domicilium.com>> 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 at 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 at 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 at 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 at 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



--
Sent from my Android device with K-9 Mail. Please excuse my brevity.
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