[Gluster-devel] Performance Translators' Stability and Usefulness

[Geoff Kassel]

Hi Anand,
   Thank you for your explanation. I appreciate the circumstances you're in - 
I'm in a not-too-dissimilar environment myself.

   If you don't mind taking some more advice - do you mind taking down your 
current QA process document? It does not seem to be an accurate 
representation of your QA process at all.

   Alternatively, you could document what you really do, and then try to 
improve on it - a technique common to many quality management methodologies. 
If that doesn't look so good at first - well, you don't have to publish it 
openly. You're running an open source project, people are prepared for things 
to be a bit rough and ready. Just don't make representations that it's 
otherwise. (Major version numbers and marketing spiel are what I'm talking 
about here.)

   Misleading people - intentionally or otherwise - kills community support 
and commercial trust in your product fast. Open source projects in particular 
need to be more open than purely commercial efforts, because not only do you 
lose users, you lose current and potential developers when this happens.

   On the code front - can you please start using code comments? It's really 
hard to follow the purpose of some parts of the code otherwise, and that 
makes it difficult for those in the community to help you fix problems or 
provide new functionality. After all, isn't getting the community to help 
write and debug the software part of the cost effectiveness of the open 
source development technique?

   (I understand that there may be language issues at stake here. But this is 
the era of automatic translation, after all - hackers like me will get along 
okay so long as we can get the gist :)

   Please don't be afraid to use code quality analysis tools, even if they do 
insert some less-than-attractive comments. Tools like RATS and FlawFinder are 
free, they catch a lot of potential and actual stability and security issues, 
and can be partially automated as part of wider testing frameworks.

   GlusterFS should be eligible to sign up to use Coverity's scan for free. 
It's a highly recommended static analysis tool, and if you make use of the 
results, there are some quite dramatic gains in stability and reliability to 
be made.

   Also having a general look over the code every now and then will do wonders 
for these aspects as well - look at the security record of OpenBSD to see how 
effective code audits can be.

   On the testing framework front - I know how hard it is to start writing 
unit and regression tests for a project already under way. The answer I've 
found to this is to get developers writing tests for the new functionality 
they write, as they write it. (Leaving it to later - say, for the QA team to 
do - makes this process a lot more difficult, as I've found.) This documents 
in live code how the system should work, and if run whenever changes to that 
functionality are made, detects breakages fast.

   When the QA team or the community uncovers a bug, get the QA team to write 
a test case covering that issue, documenting (again in live code) what the 
correct behaviour should be. Between these two activities, the coverage of 
the testing framework will improve in leaps and bounds.

   Over time, you'll develop a full regression testing suite, which, if run 
before major releases (if not before each repository commit), will save a lot 
of time and embarrassment when the occasional bug pops up to affect older 
features negatively or cause known bugs to resurface.

   Thank you for listening to me, and I hope this advice proves useful to you.

Geoff.

On Mon, 6 Jul 2009, Anand Babu Periasamy wrote:
> Gordon, Geoff, Fillipe,
>
> We are sorry!. We admit we had a rough and difficult past.
>
> Here are the reasons, why it was difficult for us:
> * Limited staff and QA environment.
> * GlusterFS is a programmable file system. It supported many OS distros,
> applications, hardware and storage architecture. It was impossible to QA
> all possible combinations. What we declared as stable is just one of many
> such use-cases.
> * Poor documentation.
>
> We are now VC funded. We have increased the size of our team and hardware
> lab significantly. 2.0 is an outcome of this investment. 2.0.3 scheduled
> for this week will be relatively lot more stable. A dedicated technical
> writer is now working on an improved version of our installation guide.  We
> are going to templatize GlusterFS stable configurations through a tool for
> generating and managing volume spec files. GlusterSP (storage platform)
> will completely automate the installation and management of a ruggedized
> release of GlusterFS in an embedded OS form. GlusterSP 2010 first beta will
> be out in 2 months. With its web based UI and pre-configured system image,
> a number of error factors are reduced.
>
> We are constantly learning and improving. You are making a valuable
> contribution by constructively criticizing us with details and proposals.
> We take them seriously and positively.
>
> Happy Hacking,
> --
> Anand Babu Periasamy
> GPG Key ID: 0x62E15A31
> Blog [http://unlocksmith.org]
> GlusterFS [http://www.gluster.org]
> GNU/Linux [http://www.gnu.org]
>
> Geoff Kassel wrote:
> > Hi Gordan,
> >
> >> What is production unready (more than Gluster) about PeerFS or SeznamFS?
> >
> > Well, I'm mostly going by your email comparing these of a few months ago.
> > Your needs are not that dissimilar to mine.
> >
> > I see on the project page for SeznamFS now that there's apparently
> > support for SeznamFS to do master-master replication 'MySQL' style - with
> > the limitations of MySQL's master-master replication, apparently.
> >
> > However, I can't seem to find out exactly what those limitations entail -
> > or how to set it up in this mode. (And I am looking for a system that
> > would allow more than two masters/peers, which is why I passed over DRBD
> > for GlusterFS originally.)
> >
> > I can't get even the PeerFS web page to load. That's a disturbing sign to
> > me.
> >
> >> You can fail over NFS servers. If the servers themselves are mirrored
> >> (DRBD) and/or have a shared file system NFS should be able to handle the
> >> IP being migrated between servers. I've found it this tends to work
> >> better with NFS over UDP provided you have a network that doesn't
> >> normally suffer packet loss.
> >
> > Sorry, thought you were talking about NFS exports from just one local
> > drive/RAID array.
> >
> > My leading fallback option for when I give up on Gluster is pretty much
> > exactly what you've just described. However - I have the same (potential)
> > issue as you with DRBD and WANs looming over my project i.e. the eventual
> > need to run masters/peers in geographically distributed sites.
> >
> >> How do you mean? GFS1 has been in the vanilla kernel for a while.
> >
> > I don't use a vanilla kernel. I use a 'hardened' kernel patched with PaX
> > and a few other security systems, to protect against stack smashing
> > attacks and other nasties. (Just a little bit of extra, relative
> > security, to make would-be attackers go after softer targets.)
> >
> > PaX is especially intolerant of memory faults in general, which is where
> > my efforts in patching GlusterFS were focused. (And yes, I have disabled
> > PaX features for Gluster. No, it didn't improve anything.)
> >
> > When I was looking into GFS, I found that the GFS patches (perhaps I was
> > looking at v2) didn't work with the hardened patchset. GlusterFS had more
> > promise than GFS anyway, so I went with GlusterFS.
> >
> >>> An older version of GlusterFS - as buggy as it is for me - is
> >>> unfortunately still the best option.
> >>
> >> Out of interest, what was the last version of Gluster did you deem
> >> completely stable?
> >
> > What works for me with only (only!) a few crashes a day, and no apparent
> > data corruption is 1.4.0tla849. TLA 636 worked a little better for me -
> > only random crashes once in a while. (But again - backwards incompatible
> > changes had crept in between the two versions, so I couldn't go back.)
> >
> > I had much better stability with the earlier 1.3 releases. I can't
> > remember exactly which ones now. (I suspect it was 1.3.3, but I'm no
> > longer sure.) It's been quite a while.
> >
> >> I don't agree on that particular point, since the last outstanding bug
> >> I'm seeing with any significant frequency in my use case is the one of
> >> having to wait for a few seconds for the FS to settle after mounting
> >> before doing anything or the operation fails. And to top it off, I've
> >> just had it succeed without the wait. That seems quite heisenbuggy/recey
> >> to me. :)
> >
> > Sorry, I was talking about the data corruption bugs. Not your
> > first-access issue.
> >
> >> That doesn't help - the first-access-settle-time bug has been around for
> >> a very long time. ;)
> >
> > Indeed.
> >
> > It's my hope that once testing frameworks (and syslog logging, in your
> > case) are made available to the community, people like us can attempt to
> > debug our systems with some degree of confidence that we're not causing
> > other subtle issues with our patches.
> >
> > That's got to be better for the project as a whole.
> >
> > Geoff.
> >
> > On Sun, 5 Jul 2009, Gordan Bobic wrote:
> >> Geoff Kassel wrote:
> >>>> Sounds like a lot of effort and micro-downtime compared to a migration
> >>>> to something else. Have you explored other options like PeerFS, GFS
> >>>> and SeznamFS? Or NFS exports with failover rather than Gluster
> >>>> clients, with Gluster only server-to-server?
> >>>
> >>> These options are not production ready (as I believe has been pointed
> >>> out already to the list) for what I need;
> >>
> >> What is production unready (more than Gluster) about PeerFS or SeznamFS?
> >>
> >>> or in the case of NFS, defeating the
> >>> point of redundancy in the first place.
> >>
> >> You can fail over NFS servers. If the servers themselves are mirrored
> >> (DRBD) and/or have a shared file system NFS should be able to handle the
> >> IP being migrated between servers. I've found it this tends to work
> >> better with NFS over UDP provided you have a network that doesn't
> >> normally suffer packet loss.
> >>
> >>> (Also, GFS is also not compatible
> >>> with the kernel patchset I need to use.)
> >>
> >> How do you mean? GFS1 has been in the vanilla kernel for a while.
> >>
> >>> I have tried AFR on the server side and the client side. Both display
> >>> similar issues.
> >>>
> >>> An older version of GlusterFS - as buggy as it is for me - is
> >>> unfortunately still the best option.
> >>
> >> Out of interest, what was the last version of Gluster did you deem
> >> completely stable?
> >>
> >>> (That doesn't mean I can't complain about the lack of progress towards
> >>> stability and reliability, though :)
> >>
> >> Heh - and would you believe I just rebooted one of my root-on-glusterfs
> >> nodes and it came up OK without the bail-out requiring manual
> >> intervention caused by the bug that causes first access after mounting
> >> to fail before things have settled.
> >>
> >>>> One of the problems is that some tests in this case are impossible to
> >>>> carry out without having multiple nodes up and running, as a number of
> >>>> bugs have been arising in cases where nodes join/leave or cause race
> >>>> conditions. It would require a distributed test harness which would be
> >>>> difficult to implement so that they run on any client that builds the
> >>>> binaries. Just because the test harness doesn't ship with the sources
> >>>> doesn't mean it doesn't exist on a test rig the developers use
> >>>
> >>> Okay, so what about the volume of test cases that can be tested without
> >>> a distributed test harness? I don't see any sign of testing mechanisms
> >>> for that.
> >>
> >> That point is hard to argue against. :)
> >>
> >>> And wouldn't it be prudent anyway - giving how often the GlusterFS devs
> >>> do not have access to the platform with the reported problem - to
> >>> provide this harness so that people can generate the appropriate test
> >>> results the devs need for themselves? (Giving a complete stranger from
> >>> overseas root access is a legal minefield to those who have to work
> >>> with data held in-confidence.)
> >>
> >> Indeed. And shifting test-case VM images tends to be impractical (even
> >> though I have provided both to the gluster developers in the past for
> >> specific error-case analysis).
> >>
> >>> It's been my impression, though, that the relevant bugs are not
> >>> heisenbugs or race conditions.
> >>
> >> I don't agree on that particular point, since the last outstanding bug
> >> I'm seeing with any significant frequency in my use case is the one of
> >> having to wait for a few seconds for the FS to settle after mounting
> >> before doing anything or the operation fails. And to top it off, I've
> >> just had it succeed without the wait. That seems quite heisenbuggy/recey
> >> to me. :)
> >>
> >>> (I'm judging that on the speed of the follow up patch, by the way -
> >>> race conditions notoriously can take a long time to track down.)
> >>
> >> That doesn't help - the first-access-settle-time bug has been around for
> >> a very long time. ;)
> >>
> >> Gordan
> >>
> >>
> >> _______________________________________________
> >> Gluster-devel mailing list
> >> Gluster-devel at nongnu.org
> >> http://lists.nongnu.org/mailman/listinfo/gluster-devel
> >
> > _______________________________________________
> > Gluster-devel mailing list
> > Gluster-devel at nongnu.org
> > http://lists.nongnu.org/mailman/listinfo/gluster-devel