[Gluster-users] Lots of connections on clients - appropriate values for various thread parameters

Fri Mar 29 06:47:30 UTC 2019

Hi Raghavendra,

i'll try to gather the information you need, hopefully this weekend.

One thing i've done this week: deactivate performance.quick-read
(https://bugzilla.redhat.com/show_bug.cgi?id=1673058), which
(according to munin) ended in a massive drop in network traffic and a
slightly lower iowait. Maybe that has helped already. We'll see.

performance.nl-cache is deactivated due to unreadable
files/directories; we have a highly concurrent workload. There are
some nginx backend webservers that check if a requested file exists in
the glusterfs filesystem; i counted the log entries, this can be up to
5 million entries a day; about 2/3 of the files are found in the
filesystem, they get delivered to the frontend; if not: the nginx's
send the  request via round robin to 3 backend tomcats, and they have
to check whether a directory exists or not (and then create it and the
requested files). So it happens that tomcatA creates a directory and a
file in it, and within (milli)seconds tomcatB+C create additional
files in this dir.

Deactivating nl-cache helped to solve this issue, after having
conversation with Nithya and Ravishankar. Just wanted to explain that.

Thx so far,
Hubert

Am Fr., 29. März 2019 um 06:29 Uhr schrieb Raghavendra Gowdappa
<rgowdapp at redhat.com>:
>
> +Gluster-users
>
> Sorry about the delay. There is nothing suspicious about per thread CPU utilization of glusterfs process. However looking at the volume profile attached I see huge number of lookups. I think if we cutdown the number of lookups probably we'll see improvements in performance. I need following information:
>
> * dump of fuse traffic under heavy load (use --dump-fuse option while mounting)
> * client volume profile for the duration of heavy load - https://docs.gluster.org/en/latest/Administrator%20Guide/Performance%20Testing/
> * corresponding brick volume profile
>
> Basically I need to find out
> * whether these lookups are on existing files or non-existent files
> * whether they are on directories or files
> * why/whether md-cache or kernel attribute cache or nl-cache will help to cut down lookups.
>
> regards,
> Raghavendra
>
> On Mon, Mar 25, 2019 at 12:13 PM Hu Bert <revirii at googlemail.com> wrote:
>>
>> Hi Raghavendra,
>>
>> sorry, this took a while. The last weeks the weather was bad -> less
>> traffic, but this weekend there was a massive peak. I made 3 profiles
>> with top, but at first look there's nothing special here.
>>
>> I also made a gluster profile (on one of the servers) at a later
>> moment. Maybe that helps. I also added some munin graphics from 2 of
>> the clients and 1 graphic of server network, just to show how massive
>> the problem is.
>>
>> Just wondering if the high io wait is related to the high network
>> traffic bug (https://bugzilla.redhat.com/show_bug.cgi?id=1673058); if
>> so, i could deactivate performance.quick-read and check if there is
>> less iowait. If that helps: wonderful - and yearningly awaiting
>> updated packages (e.g. v5.6). If not: maybe we have to switch from our
>> normal 10TB hdds (raid10) to SSDs if the problem is based on slow
>> hardware in the use case of small files (images).
>>
>>
>> Thx,
>> Hubert
>>
>> Am Mo., 4. März 2019 um 16:59 Uhr schrieb Raghavendra Gowdappa
>> <rgowdapp at redhat.com>:
>> >
>> > Were you seeing high Io-wait when you captured the top output? I guess not as you mentioned the load increases during weekend. Please note that this data has to be captured when you are experiencing problems.
>> >
>> > On Mon, Mar 4, 2019 at 8:02 PM Hu Bert <revirii at googlemail.com> wrote:
>> >>
>> >> Hi,
>> >> sending the link directly to  you and not the list, you can distribute
>> >> if necessary. the command ran for about half a minute. Is that enough?
>> >> More? Less?
>> >>
>> >> https://download.outdooractive.com/top.output.tar.gz
>> >>
>> >> Am Mo., 4. März 2019 um 15:21 Uhr schrieb Raghavendra Gowdappa
>> >> <rgowdapp at redhat.com>:
>> >> >
>> >> >
>> >> >
>> >> > On Mon, Mar 4, 2019 at 7:47 PM Raghavendra Gowdappa <rgowdapp at redhat.com> wrote:
>> >> >>
>> >> >>
>> >> >>
>> >> >> On Mon, Mar 4, 2019 at 4:26 PM Hu Bert <revirii at googlemail.com> wrote:
>> >> >>>
>> >> >>> Hi Raghavendra,
>> >> >>>
>> >> >>> at the moment iowait and cpu consumption is quite low, the main
>> >> >>> problems appear during the weekend (high traffic, especially on
>> >> >>> sunday), so either we have to wait until next sunday or use a time
>> >> >>> machine ;-)
>> >> >>>
>> >> >>> I made a screenshot of top (https://abload.de/img/top-hvvjt2.jpg) and
>> >> >>> a text output (https://pastebin.com/TkTWnqxt), maybe that helps. Seems
>> >> >>> like processes like glfs_fuseproc (>204h) and glfs_epoll (64h for each
>> >> >>> process) consume a lot of CPU (uptime 24 days). Is that already
>> >> >>> helpful?
>> >> >>
>> >> >>
>> >> >> Not much. The TIME field just says the amount of time the thread has been executing. Since its a long standing mount, we can expect such large values. But, the value itself doesn't indicate whether the thread itself was overloaded at any (some) interval(s).
>> >> >>
>> >> >> Can you please collect output of following command and send back the collected data?
>> >> >>
>> >> >> # top -bHd 3 > top.output
>> >> >
>> >> >
>> >> > Please collect this on problematic mounts and bricks.
>> >> >
>> >> >>
>> >> >>>
>> >> >>>
>> >> >>> Hubert
>> >> >>>
>> >> >>> Am Mo., 4. März 2019 um 11:31 Uhr schrieb Raghavendra Gowdappa
>> >> >>> <rgowdapp at redhat.com>:
>> >> >>> >
>> >> >>> > what is the per thread CPU usage like on these clients? With highly concurrent workloads we've seen single thread that reads requests from /dev/fuse (fuse reader thread) becoming bottleneck. Would like to know what is the cpu usage of this thread looks like (you can use top -H).
>> >> >>> >
>> >> >>> > On Mon, Mar 4, 2019 at 3:39 PM Hu Bert <revirii at googlemail.com> wrote:
>> >> >>> >>
>> >> >>> >> Good morning,
>> >> >>> >>
>> >> >>> >> we use gluster v5.3 (replicate with 3 servers, 2 volumes, raid10 as
>> >> >>> >> brick) with at the moment 10 clients; 3 of them do heavy I/O
>> >> >>> >> operations (apache tomcats, read+write of (small) images). These 3
>> >> >>> >> clients have a quite high I/O wait (stats from yesterday) as can be
>> >> >>> >> seen here:
>> >> >>> >>
>> >> >>> >> client: https://abload.de/img/client1-cpu-dayulkza.png
>> >> >>> >> server: https://abload.de/img/server1-cpu-dayayjdq.png
>> >> >>> >>
>> >> >>> >> The iowait in the graphics differ a lot. I checked netstat for the
>> >> >>> >> different clients; the other clients have 8 open connections:
>> >> >>> >> https://pastebin.com/bSN5fXwc
>> >> >>> >>
>> >> >>> >> 4 for each server and each volume. The 3 clients with the heavy I/O
>> >> >>> >> have (at the moment) according to netstat 170, 139 and 153
>> >> >>> >> connections. An example for one client can be found here:
>> >> >>> >> https://pastebin.com/2zfWXASZ
>> >> >>> >>
>> >> >>> >> gluster volume info: https://pastebin.com/13LXPhmd
>> >> >>> >> gluster volume status: https://pastebin.com/cYFnWjUJ
>> >> >>> >>
>> >> >>> >> I just was wondering if the iowait is based on the clients and their
>> >> >>> >> workflow: requesting a lot of files (up to hundreds per second),
>> >> >>> >> opening a lot of connections and the servers aren't able to answer
>> >> >>> >> properly. Maybe something can be tuned here?
>> >> >>> >>
>> >> >>> >> Especially the server|client.event-threads (both set to 4) and
>> >> >>> >> performance.(high|normal|low|least)-prio-threads (all at default value
>> >> >>> >> 16) and performance.io-thread-count (32) options, maybe these aren't
>> >> >>> >> properly configured for up to 170 client connections.
>> >> >>> >>
>> >> >>> >> Both servers and clients have a Xeon CPU (6 cores, 12 threads), a 10
>> >> >>> >> GBit connection and 128G (servers) respectively 256G (clients) RAM.
>> >> >>> >> Enough power :-)
>> >> >>> >>
>> >> >>> >>
>> >> >>> >> Thx for reading && best regards,
>> >> >>> >>
>> >> >>> >> Hubert
>> >> >>> >> _______________________________________________
>> >> >>> >> Gluster-users mailing list
>> >> >>> >> Gluster-users at gluster.org
>> >> >>> >> https://lists.gluster.org/mailman/listinfo/gluster-users