[Gluster-users] SQLite3 on 3 node cluster FS?

Tue Mar 6 17:28:40 UTC 2018

On Tue, Mar 6, 2018 at 10:22 PM, Paul Anderson <pha at umich.edu> wrote:

> Raghavendra,
>
> I've commited my tests case to https://github.com/powool/gluster.git -
> it's grungy, and a work in progress, but I am happy to take change
> suggestions, especially if it will save folks significant time.
>
> For the rest, I'll reply inline below...
>
> On Mon, Mar 5, 2018 at 10:39 PM, Raghavendra Gowdappa
> <rgowdapp at redhat.com> wrote:
> > +Csaba.
> >
> > On Tue, Mar 6, 2018 at 2:52 AM, Paul Anderson <pha at umich.edu> wrote:
> >>
> >> Raghavendra,
> >>
> >> Thanks very much for your reply.
> >>
> >> I fixed our data corruption problem by disabling the volume
> >> performance.write-behind flag as you suggested, and simultaneously
> >> disabling caching in my client side mount command.
> >
> >
> > Good to know it worked. Can you give us the output of
> > # gluster volume info
>
> [root at node-1 /]# gluster volume info
>
> Volume Name: dockerstore
> Type: Replicate
> Volume ID: fb08b9f4-0784-4534-9ed3-e01ff71a0144
> Status: Started
> Snapshot Count: 0
> Number of Bricks: 1 x 3 = 3
> Transport-type: tcp
> Bricks:
> Brick1: 172.18.0.4:/data/glusterfs/store/dockerstore
> Brick2: 172.18.0.3:/data/glusterfs/store/dockerstore
> Brick3: 172.18.0.2:/data/glusterfs/store/dockerstore
> Options Reconfigured:
> performance.client-io-threads: off
> nfs.disable: on
> transport.address-family: inet
> locks.mandatory-locking: optimal
> performance.flush-behind: off
> performance.write-behind: off
>
> >
> > We would like to debug the problem in write-behind. Some questions:
> >
> > 1. What version of Glusterfs are you using?
>
> On the server nodes:
>
> [root at node-1 /]# gluster --version
> glusterfs 3.13.2
> Repository revision: git://git.gluster.org/glusterfs.git
>
> On the docker container sqlite test node:
>
> root at b4055d8547d2:/# glusterfs --version
> glusterfs 3.8.8 built on Jan 11 2017 14:07:11
>

I guess this is where client is mounted. If I am correct on where glusterfs
client is mounted, client is running quite a old version. There have been
significant number of fixes between 3.8.8 and current master. I would
suggest to try out 3.13.2 patched with [1]. If you get a chance to try this
out, please report back how did the tests go.

[1] https://review.gluster.org/19673

> I recognize that version skew could be an issue.
>
> > 2. Were you able to figure out whether its stale data or metadata that is
> > causing the issue?
>
> I lean towards stale data based on the only real observation I have:
>
> While debugging, I put log messages in as to when the flock() is
> acquired, and when it is released. There is no instance where two
> different processes ever hold the same flock()'d file. From what I
> have read, the locks are considered metadata, and they appear to me to
> be working, so that's why I'm inclined to think stale data is the
> issue.
>
> >
> > There have been patches merged in write-behind in recent past and one in
> the
> > works which address metadata consistency. Would like to understand
> whether
> > you've run into any of the already identified issues.
>
> Agreed!
>
> Thanks,
>
> Paul
>
> >
> > regards,
> > Raghavendra
> >>
> >>
> >> In very modest testing, the flock() case appears to me to work well -
> >> before it would corrupt the db within a few transactions.
> >>
> >> Testing using built in sqlite3 locks is better (fcntl range locks),
> >> but has some behavioral issues (probably just requires query retry
> >> when the file is locked). I'll research this more, although the test
> >> case is not critical to our use case.
> >>
> >> There are no signs of O_DIRECT use in the sqlite3 code that I can see.
> >>
> >> I intend to set up tests that run much longer than a few minutes, to
> >> see if there are any longer term issues. Also, I want to experiment
> >> with data durability by killing various gluster server nodes during
> >> the tests.
> >>
> >> If anyone would like our test scripts, I can either tar them up and
> >> email them or put them in github - either is fine with me. (they rely
> >> on current builds of docker and docker-compose)
> >>
> >> Thanks again!!
> >>
> >> Paul
> >>
> >> On Mon, Mar 5, 2018 at 11:26 AM, Raghavendra Gowdappa
> >> <rgowdapp at redhat.com> wrote:
> >> >
> >> >
> >> > On Mon, Mar 5, 2018 at 8:21 PM, Paul Anderson <pha at umich.edu> wrote:
> >> >>
> >> >> Hi,
> >> >>
> >> >> tl;dr summary of below: flock() works, but what does it take to make
> >> >> sync()/fsync() work in a 3 node GFS cluster?
> >> >>
> >> >> I am under the impression that POSIX flock, POSIX
> >> >> fcntl(F_SETLK/F_GETLK,...), and POSIX read/write/sync/fsync are all
> >> >> supported in cluster operations, such that in theory, SQLite3 should
> >> >> be able to atomically lock the file (or a subset of page), modify
> >> >> pages, flush the pages to gluster, then release the lock, and thus
> >> >> satisfy the ACID property that SQLite3 appears to try to accomplish
> on
> >> >> a local filesystem.
> >> >>
> >> >> In a test we wrote that fires off 10 simple concurrernt SQL insert,
> >> >> read, update loops, we discovered that we at least need to use
> flock()
> >> >> around the SQLite3 db connection open/update/close to protect it.
> >> >>
> >> >> However, that is not enough - although from testing, it looks like
> >> >> flock() works as advertised across gluster mounted files, sync/fsync
> >> >> don't appear to, so we end up getting corruption in the SQLite3 file
> >> >> (pragma integrity_check generally will show a bunch of problems after
> >> >> a short test).
> >> >>
> >> >> Is what we're trying to do achievable? We're testing using the docker
> >> >> container gluster/gluster-centos as the three servers, with a php
> test
> >> >> inside of php-cli using filesystem mounts. If we mount the gluster FS
> >> >> via sapk/plugin-gluster into the php-cli containers using docker, we
> >> >> seem to have better success sometimes, but I haven't figured out why,
> >> >> yet.
> >> >>
> >> >> I did see that I needed to set the server volume parameter
> >> >> 'performance.flush-behind off', otherwise it seems that flushes won't
> >> >> block as would be needed by SQLite3.
> >> >
> >> >
> >> > If you are relying on fsync this shouldn't matter as fsync makes sure
> >> > data
> >> > is synced to disk.
> >> >
> >> >>
> >> >> Does anyone have any suggestions? Any words of widsom would be much
> >> >> appreciated.
> >> >
> >> >
> >> > Can you experiment with turning on/off various performance xlators?
> >> > Based on
> >> > earlier issues, its likely that there is stale metadata which might be
> >> > causing the issue (not necessarily improper fsync behavior). I would
> >> > suggest
> >> > turning off all performance xlators. You can refer [1] for a related
> >> > discussion. In theory the only perf xlator relevant for fsync is
> >> > write-behind and I am not aware of any issues where fsync is not
> >> > working.
> >> > Does glusterfs log file has any messages complaining about writes or
> >> > fsync
> >> > failing? Does your application use O_DIRECT? If yes, please note that
> >> > you
> >> > need to turn the option performance.strict-o-direct on for
> write-behind
> >> > to
> >> > honour O_DIRECT
> >> >
> >> > Also, is it possible to identify nature of corruption - Data or
> >> > metadata?
> >> > More detailed explanation will help to RCA the issue.
> >> >
> >> > Also, is your application running on a single mount or from multiple
> >> > mounts?
> >> > Can you collect strace of your application (strace -ff -T -p <pid> -o
> >> > <file>)? If possible can you also collect fuse-dump using option
> >> > --dump-fuse
> >> > while mounting glusterfs?
> >> >
> >> > [1]
> >> >
> >> > http://lists.gluster.org/pipermail/gluster-users/2018-
> February/033503.html
> >> >
> >> >>
> >> >> Thanks,
> >> >>
> >> >> Paul
> >> >> _______________________________________________
> >> >> Gluster-users mailing list
> >> >> Gluster-users at gluster.org
> >> >> http://lists.gluster.org/mailman/listinfo/gluster-users
> >> >
> >> >
> >
> >
>
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