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

Fri Oct 23 09:37:26 UTC 2015

Hi John,

Thanks for trying out glusterfind and reporting issues. To use 
glusterfind without session, Milind is planning to introduce a new 
option called "query".

`glusterfind query` will accept the timestamp as parameter and gets the 
list of files changed after that time.
Patch: http://review.gluster.org/#/c/12362/

Glusterfind is doing crawl in brick backend if a file path is not 
recorded in Changelogs(Only GFID is recorded in Changelogs). This may be 
the reason for the CPU utilization. We are working on the solution which 
simplifies the conversion of GFID to path, so that crawl can be avoided 
to find path.

regards
Aravinda

On 10/23/2015 02:54 PM, Sincock, John [FLCPTY] wrote:
> 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!
>>
>>
>> _______________________________________________
>> Gluster-devel mailing list
>> Gluster-devel at gluster.org
>> http://www.gluster.org/mailman/listinfo/gluster-devel
> _______________________________________________
> Gluster-devel mailing list
> Gluster-devel at gluster.org
> http://www.gluster.org/mailman/listinfo/gluster-devel