[Gluster-devel] Need advice re some major issues with glusterfind

[Sincock, John [FLCPTY]]

Hi Kotresh,

NP, thanks for clarifying that Kotresh. We will be sure to delete or archive only changelogs that are old enough we're sure we won't need to query them.

Cheers and thanks again :-)


-----Original Message-----
From: Kotresh Hiremath Ravishankar [mailto:khiremat at redhat.com] 
Sent: Friday, 23 October 2015 8:30 PM
To: Sincock, John [FLCPTY]
Cc: Vijaikumar Mallikarjuna; gluster-devel at gluster.org
Subject: Re: [Gluster-devel] Need advice re some major issues with glusterfind

Hi John,

You are welcome and happy to help you!

You can delete the consumed changelogs safely if there is only one glusterfind session for your gluster volume. But if you have multiple glusterfind sessions which are started at time gap of let's say two days.

1st-day  : session1   ----- For Purpose 1
2nd-day  : session1
3rd-day  : session1
           session2 (started)  ----- For Purpose 2

Above, if you had deleted changelogs of Day-1 and Day-2 when session 2 is started, it needs to crawl the entire filesystem which defeats the purpose of glusterfind and is slower.
That's the reason I said deleting changelogs is not recommended. If you don't have use cases of above kind, you can delete changelogs.


Thanks and Regards,
Kotresh H R

----- Original Message -----
> From: "John Sincock [FLCPTY]" <J.Sincock at fugro.com>
> To: "Kotresh Hiremath Ravishankar" <khiremat at redhat.com>
> Cc: "Vijaikumar Mallikarjuna" <vmallika at redhat.com>, 
> gluster-devel at gluster.org
> Sent: Friday, October 23, 2015 2:54:14 PM
> Subject: RE: [Gluster-devel] Need advice re some major issues with 
> glusterfind
> 
> Aaah I seeee, thanks Kotresh :-)
> This explains why there are so many files and why I sometimes didn't 
> see some changed files during my testing where I was changing files 
> and then immediately running a glusterfind.
> 
> When you say deleting the changelogs is not recommended because it 
> will affect new glusterfind sessions - I assume it will be OK to 
> delete changelogs that are further back into the past than the time 
> period we're interested in? Please let me know if this is the case, or 
> if you meant that removing old changelogs is likely to trigger bugs 
> and cause all our glusterfinds to start failing outright...
> 
> We can leave the old changelogs there if we have to, but if we don’t 
> increase the rollover time, the number will become astronomical as 
> time goes on, so I hope we can delete or archive old changelogs for 
> time periods we're no longer interested in.
> 
> For our purposes I think it should also be OK to try increasing the 
> rollover time significantly, eg if we have it set to rollover every 10 
> minutes, then all we have to do is subtract 10 mins from the start 
> time of each glusterfind/backup so it overlaps the end of the previous 
> glusterfind period. In this way, any files changed just before a 
> glusterfind/backup runs, might be missed by the first backup, but they 
> will be caught by the next backup that runs later on. And it wont 
> matter if some changed files get backed up twice -as long as we get at 
> least one backup of every file that does change..
> 
> I note that by default there is no easy way to make glusterfind report 
> on changes further back in time than the time you run glusterfind 
> create to start a session - but I've already had some success at 
> getting glusterfind to give results back to earlier times before the 
> session was created (as long as the changelogs exist). I did this by 
> using a script to manually set the time we're interested in in the 
> status file(s) - ie in the main status file on the node running the 
> "pre" command", and for every one of the extra status files stored on 
> every node for each of their bricks :-)
> 
> I think my only remaining concern is how cpu-intensive the process is. 
> I've had glusterfinds return very quickly if only reporting on changes 
> for the last hour, or the last 10 hours or so. But if I go back a bit 
> further, the time taken to do the glusterfind seems to really blow out 
> and it sits there pegging all our CPUs at 100% for hours.
> 
> But you and Vijay have definitely given me a few tweaks I can look 
> into - I think I will bump-up the changelog rollover a bit, and will 
> follow Vijay's tip to get all our files labelled with pgfid's, and 
> then perhaps the glusterfinds will be less cpu-intensive.
> 
> Thanks for the tips (Kotresh & Vijay), and I'll let you know how it goes.
> 
> If the glusterfinds are still very cpu-intensive after all the pgfid 
> labelling is done, I'll be happy to do some further testing if it can 
> be of any help to you. Or if you're already trying to find time to 
> work on increasing the efficiency of processing the changelogs, and 
> you know where the improvements need to be made I'll just leave you to 
> it and hope it all goes smoothly for you
> 
> Thanks again, and cheerios :-)
> John
> 
> 
> 
> 
> 
>  
> 
> 
> 
> 
> -----Original Message-----
> From: Kotresh Hiremath Ravishankar [mailto:khiremat at redhat.com]
> Sent: Friday, 23 October 2015 5:24 PM
> To: Sincock, John [FLCPTY]
> Cc: Vijaikumar Mallikarjuna; gluster-devel at gluster.org
> Subject: Re: [Gluster-devel] Need advice re some major issues with 
> glusterfind
> 
> Hi John,
> 
> The changelog files are generated every 15 secs recording the changes 
> happened to filesystem within that span.  So every 15 sec, once the 
> new changelog file is generated, it is ready to be consumed by 
> glusterfind or any other consumers. The 15 sec time period is a tune-able.
> e.g.,
>      gluster vol set <VOLNAME> changelog.rollover-time 300
> 
> The above will generate new changelog file every 300 sec instead of 15 sec.
> Hence reducing the number of changelogs. But glusterfind, will come to 
> know about the changes in filesystem only after 300 secs!
> 
> Deleting these changelogs at .glusterfs/changelog/... is not 
> recommeneded. It will affect any new glusterfind session going to be established.
> 
> 
> Thanks and Regards,
> Kotresh H R1
> 
> ----- Original Message -----
> > From: "John Sincock [FLCPTY]" <J.Sincock at fugro.com>
> > To: "Vijaikumar Mallikarjuna" <vmallika at redhat.com>
> > Cc: gluster-devel at gluster.org
> > Sent: Friday, October 23, 2015 9:54:25 AM
> > Subject: Re: [Gluster-devel] Need advice re some major issues with 
> > glusterfind
> > 
> > 
> > Hi Vijay, pls see below again (I'm wondering if top-posting would be 
> > easier, that's usually what I do, though I know some ppl don’t like
> > it)
> > 
> >  
> > On Wed, Oct 21, 2015 at 5:53 AM, Sincock, John [FLCPTY] 
> > <J.Sincock at fugro.com>
> > wrote:
> > Hi Everybody,
> > 
> > We have recently upgraded our 220 TB gluster to 3.7.4, and we've 
> > been trying to use the new glusterfind feature but have been having 
> > some serious problems with it. Overall the glusterfind looks very 
> > promising, so I don't want to offend anyone by raising these issues.
> > 
> > If these issues can be resolved or worked around, glusterfind will 
> > be a great feature.  So I would really appreciate any information or advice:
> > 
> > 1) What can be done about the vast number of tiny changelogs? We are 
> > seeing often 5+ small 89 byte changelog files per minute on EACH 
> > brick. Larger files if busier. We've been generating these 
> > changelogs for a few weeks and have in excess of 10,000 or 12,000 on most bricks.
> > This makes glusterfinds very, very slow, especially on a node which 
> > has a lot of bricks, and looks unsustainable in the long run. Why 
> > are these files so small, and why are there so many of them, and how 
> > are they supposed to be managed in the long run? The sheer number of 
> > these files looks sure to impact performance in the long run.
> > 
> > 2) Pgfid xattribute is wreaking havoc with our backup scheme - when 
> > gluster adds this extended attribute to files it changes the ctime, 
> > which we were using to determine which files need to be archived.
> > There should be a warning added to release notes & upgrade notes, so 
> > people can make a plan to manage this if required.
> > 
> > Also, we ran a rebalance immediately after the 3.7.4 upgrade, and 
> > the rebalance took 5 days or so to complete, which looks like a 
> > major speed improvement over the more serial rebalance algorithm, so 
> > that's good. But I was hoping that the rebalance would also have had 
> > the side-effect of triggering all files to be labelled with the 
> > pgfid attribute by the time the rebalance completed, or failing 
> > that, after creation of an mlocate database across our entire 
> > gluster (which would have accessed every file, unless it is getting 
> > the info it needs only from directory inodes). Now it looks like 
> > ctimes are still being modified, and I think this can only be caused 
> > by files still being labelled with pgfids.
> > 
> > How can we force gluster to get this pgfid labelling over and done 
> > with, for all files that are already on the volume? We can't have 
> > gluster continuing to add pgfids in bursts here and there, eg when 
> > files are read for the first time since the upgrade. We need to get 
> > it over and done with. We have just had to turn off pgfid creation 
> > on the volume until we can force gluster to get it over and done with in one go.
> >  
> >  
> > Hi John,
> >  
> > Was quota turned on/off before/after performing re-balance? If the 
> > pgfid is
> >  missing, this can be healed by performing 'find <mount_point> | 
> > xargs stat', all the files will get looked-up once and the pgfid 
> > healing will happen.
> > Also could you please provide all the volume files under 
> > '/var/lib/glusterd/vols/<volname>/*.vol'?
> >  
> > Thanks,
> > Vijay
> >  
> >  
> > Hi Vijay
> >  
> > Quota has never been turned on in our gluster, so it can’t be any 
> > quota-related xattrs which are resetting our ctimes, so I’m pretty 
> > sure it must be due to pgfids still being added.
> >  
> > Thanks for the tip re using stat, if that should trigger the pgfid 
> > build on each file, then I will run that when I have a chance. We’ll 
> > have to get our archiving of data back up to date, re-enable pgfid 
> > build option, and then run the stat over a weekend or something, as 
> > it will take a while.
> >  
> > I’m still quite concerned about the number of changelogs being 
> > generated. Do you know if there any plans to change the way 
> > changelogs are generated so there aren’t so many of them, and to 
> > process them more efficiently? I think this will be vital to 
> > improving performance of glusterfind in future, as there are 
> > currently an enormous number of these small changelogs being generated on each of our gluster bricks.
> >   
> > Below is the volfile for one brick, the others are all equivalent. 
> > We haven’t tweaked the volume options much, besides increasing the 
> > io thread count to 32, and client/event threads to 6 (since we have 
> > a lot of small files on our gluster (30 million files, a lot of 
> > which are small, and some of which are large to very large):
> >  
> > 
> > Hi John,
> > 
> > PGFID xattrs are updated only when update-link-count-parent is 
> > enabled in the brick volume file. This option is enabled when quota 
> > is enabled on a volume.
> > In the volume file you provided below has update-link-count-parent 
> > disabled, I am wondering why PGFID xattrs are updated.
> > 
> > Thanks,
> > Vijay
> >  
> > 
> > Hi Vijay,
> > somewhere in the 3.7.5 upgrade instructions or the glusterfind 
> > documentation, there was a mention that we should enable a server 
> > option called storage.build-pgfid, which we did as it speeds up 
> > glusterfinds. You cannot see this in the volfile but you can see it 
> > when you do gluster volume info volname. So for our volume we 
> > currently
> > have:
> > 
> > Options Reconfigured:
> > server.allow-insecure: on
> > nfs.disable: false
> > performance.io-thread-count: 32
> > features.quota: off
> > client.bind-insecure: on
> > 
> > storage.build-pgfid: off
> > 
> > changelog.changelog: on
> > changelog.capture-del-path: on
> > server.event-threads: 6
> > client.event-threads: 6
> > 
> > We've turned storage.build-pgfid OFF now, but we turned it on when 
> > we did the upgrade to 3.7.4, and we had it on until a few days ago. 
> > So, for us, with update-link-count-parent off - storage.build-pgfid 
> > would've been the thing responsible for adding the pgfids to files 
> > on our volume.
> > 
> > I should've realised the best thing to do would’ve been to do a stat 
> > on every file, in order to trigger the pgfid build, but at first I 
> > thought the pgfids would be added to every file during the rebalance 
> > which was a priority at the time (we had just added 40TB of new 
> > bricks to a very full volume), and then we hit pgfid/backup issues etc.
> > 
> > I think we can get the pgfid issue resolved now you've confirmed 
> > that a stat will do it (thanks :-) We'll just have to stop our 
> > clients writing to the volume for a day or so while we stat every 
> > file on the volume. Then, if we've stopped our clients writing 
> > during that time, we can re-jig our backups to safely ignore any 
> > changed ctimes that've changed during the day or so we were stating the volume.
> > 
> > I'll let you know how things go with the pgfid's if we can get them 
> > turned back on and added to every file sometime as soon as possible.
> > 
> > I'm definitely more concerned now about the changelog issue. As 
> > mentioned we have an enormous number of these, eg as of now (about 
> > 25 days since upgrading to 3.7.4), we have 13000 or so changelogs on 
> > each of our bricks:
> > 
> > ls -la /mnt/glusterfs/bricks/1/.glusterfs/changelogs/ | wc -l
> > 13096
> > 
> > And they are very small, about 5 KB on average, and ranging from 
> > (many at
> > just) 89 bytes, up to 20 KB or so for the larger ones:
> > du -hs /mnt/glusterfs/bricks/1/.glusterfs/changelogs/
> > 68M     /mnt/glusterfs/bricks/1/.glusterfs/changelogs/
> > 
> > The size of the changelogs is not an issue (68M for almost a month 
> > worth of changes is nothing), but the sheer number of files is, as 
> > is the fact that it seems to be very cpu-intensive to process these 
> > files (eg an strace showed glusterfind taking 2.7 million system 
> > calls to process just one of these small changelogs).
> > 
> > Do you know if anyone is working on reducing the number of these 
> > changelogs and/or processing them more efficiently?
> > 
> > Thanks again for any info!
> > 
> > 
> > _______________________________________________
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> 
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