[users at bb.net] And even more multi-master anecdotes.

[Pierre Tardy]

Hi guys,

Thanks for the update. Sounds like you are having a lot of fun.. or not.

Buildbot has a Janitor since a few releases:
http://docs.buildbot.net/latest/manual/cfg-configurators.html#janitorconfigurator
I think it might be time for you to improve this and also cleanup beyond
the log. the build requests, as it looks like this is going needlessly out
of control.

Buildbot REST api do not prevent the user to shot in your foot.

I find it practical to enable people to just query for all builds, but at a
certain scale this might be too damaging for the team to allow people to
kill the server memory by just doing http://bbot/api/v2/buildrequests

So we may want to allow administrator to  enforce maximal limits in the
REST API service.
This means that if people want more, they deal with paging in their
scripts. gitlab has a default policy of 100 for all their queries.

The numbers you report does not look abnormal given your scale.
You are right that the python will never free the heap (afaik)
If at a time a process allocated 6GB of dicts, then python will release the
dicts, but not the memory. The next time, it will reuse that memory.
So you will always see python memory usage growing, and for me its not a
bad idea to rolling reboot your masters from time to time.

datetime objects are used internally in the data api to represent dates.
Might be a bit of a overkill as they are just created in data api, and
converted back to timestamps in json api.

Having 1000 incomplete buildrequests might be indeed a bit high. I think
that there are some algorithms in the scheduling that are O(N2) N being the
number of buildrequest for a particular builder. That is the result of the
very big flexibility that the build request distributor has, and there is
not so much we can do quickly.

I recently looked at this recently, which is interesting:
https://github.com/kubernetes/community/blob/master/sig-scalability/goals.md

   1. Scale for the sake of scale can lead to unnecessarily complex system
   designs: Many relatively simple system designs have large, but not
   infinite, natural scaling limits, and in order to go beyond those limits,
   more complex designs become necessary. Unless the need for the additional
   scale can be justified, the additional complexity often cannot be.



On Fri, Aug 18, 2017 at 4:41 PM Neil Gilmore <ngilmore at grammatech.com>
wrote:

> Hi again,
>
> This morning's update, after spending some quality time trying to figure
> out just what's going on...
>
> We stuffed in some of the google perftools stuff to try to see where
> memory was going. That didn't tell us much, other than there's a bunch of
> data in dictionaries (big surprise there).
>
> Top was showing a reserve much higher than the current memory usage. Not
> surprising if python isn't actually giving memory back and that's acting as
> a high water mark.
>
> Last night, when people were less likely to be around, my boss attached
> gdb to our UI master. According to him, it spends quite a bit of time
> dealing with lists of 2 million build requests.His synopsis is that it
> makes a sql query that results in 2 million build requests, does stuff with
> them, then spends time freeing them.
>
> We also spent a bit of time in the http logs. We were certainly able to
> spike memory usage by hitting the REST api.
>
> Which, as it turns out, some of our users do. One of them says that UI is
> 'too slow', so she's grabbing the info she needs every 10 minutes. Another
> has a python script that grabs various combinations of builds and builders.
> But he had, at least last night, 202 processes running that script, because
> it didn't check to see if the previous run had finished. And he had it
> running in cron.
>
> That's a bit like having an extra couple hundred users hammering the UI at
> once. I haven't exactly explored that side of the code, but I can envision
> scenarios that might spike memory to the point where the system kills it.
>
> I doubt that any of this is new. It was probably people trying to work
> around the limitations of our old, single-master, 0.8.x installation.
>
> This morning, after killing those scripts and the cron job, top looks a
> lot better. That master is using about 1.3G. Under our old conditions, it
> blows past that in the first couple minutes it's running.
>
> We'll see how it does the rest of today. I did have to restart that other
> master again.
>
>
> Neil Gilmore
> grammatech.com
>
>
> On 8/17/2017 10:10 AM, Neil Gilmore wrote:
>
> Hi everyone.
>
> This is a sort of extension to my original message.
>
> I had to restart one of our other masters this morning. It apparently lost
> its WAMP connection, whihc happens on occasion. The symptoms are that none
> of its builders show up in the UI. The master itself was running, though it
> may depend on the definition of 'running'. The process was present, but it
> sat for minutes after its last log message, which is very unusual for that
> master (it's the one that does most of the builds).
>
> I've also found that the stop command is nearly useless for our masters.
> If they've been up for a while, doing things, they don't ever seem to
> actually shut down. In this morning's case, I did the stop command. The log
> showed the process getting the SIGTERM. Then I waited for 10 minutes. The
> process didn't stop. I finally killed it (and a regular kill won't do it, I
> have to -9) because I have people asking me about it constantly when it's
> not working right.
>
> I'll also point out that we've been accumulating integrity errors in the
> database again. They look like this in the UI master's log:
>
>         sqlalchemy.exc.IntegrityError: (IntegrityError) update or delete
> on table "changes" violates foreign key constraint
> "changes_parent_changeids_fkey" on table "changes"
>         DETAIL:  Key (changeid)=(4188) is still referenced from table
> "changes".
>          'DELETE FROM changes WHERE changes.changeid IN (%(changeid_1)s,
> %(changeid_2)s, %(changeid_3)s, %(changeid_4)s, %(changeid_5)s,
> %(changeid_6)s, %(changeid_7)s, %(changeid_8)s, %(changeid_9)s,
> %(changeid_10)s, %(changeid_11)s, %(changeid_12)s, %(changeid_13)s,
> %(changeid_14)s, %(changeid_15)s, %(changeid_16)s, %(changeid_17)s,
> %(changeid_18)s, %(changeid_19)s, %(changeid_20)s, %(changeid_21)s,
> %(changeid_22)s, %(changeid_23)s, %(changeid_24)s, %(changeid_25)s,
> %(changeid_26)s, %(changeid_27)s, %(changeid_28)s, %(changeid_29)s,
> %(changeid_30)s, %(changeid_31)s, %(changeid_32)s, %(changeid_33)s,
> %(changeid_34)s, %(changeid_35)s, %(changeid_36)s, %(changeid_37)s,
> %(changeid_38)s, %(changeid_39)s, %(changeid_40)s, %(changeid_41)s,
> %(changeid_42)s, %(changeid_43)s, %(changeid_44)s, %(changeid_45)s,
> %(changeid_46)s, %(changeid_47)s, %(changeid_48)s, %(changeid_49)s,
> %(changeid_50)s, %(changeid_51)s, %(changeid_52)s, %(changeid_53)s,
> %(changeid_54)s, %(changeid_55)s, %(changeid_56)s, %(changeid_57)s,
> %(changeid_58)s, %(changeid_59)s, %(changeid_60)s, %(changeid_61)s,
> %(changeid_62)s, %(changeid_63)s, %(changeid_64)s, %(changeid_65)s,
> %(changeid_66)s, %(changeid_67)s, %(changeid_68)s, %(changeid_69)s,
> %(changeid_70)s, %(changeid_71)s, %(changeid_72)s, %(changeid_73)s,
> %(changeid_74)s, %(changeid_75)s, %(changeid_76)s, %(changeid_77)s,
> %(changeid_78)s, %(changeid_79)s, %(changeid_80)s, %(changeid_81)s,
> %(changeid_82)s, %(changeid_83)s, %(changeid_84)s, %(changeid_85)s,
> %(changeid_86)s, %(changeid_87)s, %(changeid_88)s, %(changeid_89)s,
> %(changeid_90)s, %(changeid_91)s, %(changeid_92)s, %(changeid_93)s,
> %(changeid_94)s, %(changeid_95)s, %(changeid_96)s, %(changeid_97)s,
> %(changeid_98)s, %(changeid_99)s, %(changeid_100)s)' {'changeid_100': 4180,
> 'changeid_29': 4251, 'changeid_28': 4252, 'changeid_27': 4253,
> 'changeid_26': 4254, 'changeid_25': 4255, 'changeid_24': 4256,
> 'changeid_23': 4257, 'changeid_22': 4258, 'changeid_21': 4259,
> 'changeid_20': 4260, 'changeid_89': 4191, 'changeid_88': 4192,
> 'changeid_81': 4199, 'changeid_80': 4200, 'changeid_83': 4197,
> 'changeid_82': 4198, 'changeid_85': 4195, 'changeid_84': 4196,
> 'changeid_87': 4193, 'changeid_86': 4194, 'changeid_38': 4242,
> 'changeid_39': 4241, 'changeid_34': 4246, 'changeid_35': 4245,
> 'changeid_36': 4244, 'changeid_37': 4243, 'changeid_30': 4250,
> 'changeid_31': 4249, 'changeid_32': 4248, 'changeid_33': 4247,
> 'changeid_98': 4182, 'changeid_99': 4181, 'changeid_96': 4184,
> 'changeid_97': 4183, 'changeid_94': 4186, 'changeid_95': 4185,
> 'changeid_92': 4188, 'changeid_93': 4187, 'changeid_90': 4190,
> 'changeid_91': 4189, 'changeid_63': 4217, 'changeid_62': 4218,
> 'changeid_61': 4219, 'changeid_60': 4220, 'changeid_67': 4213,
> 'changeid_66': 4214, 'changeid_65': 4215, 'changeid_64': 4216,
> 'changeid_69': 4211, 'changeid_68': 4212, 'changeid_16': 4264,
> 'changeid_17': 4263, 'changeid_14': 4266, 'changeid_15': 4265,
> 'changeid_12': 4268, 'changeid_13': 4267, 'changeid_10': 4270,
> 'changeid_11': 4269, 'changeid_18': 4262, 'changeid_19': 4261,
> 'changeid_70': 4210, 'changeid_71': 4209, 'changeid_72': 4208,
> 'changeid_73': 4207, 'changeid_74': 4206, 'changeid_75': 4205,
> 'changeid_76': 4204, 'changeid_77': 4203, 'changeid_78': 4202,
> 'changeid_79': 4201, 'changeid_45': 4235, 'changeid_44': 4236,
> 'changeid_47': 4233, 'changeid_46': 4234, 'changeid_41': 4239,
> 'changeid_40': 4240, 'changeid_43': 4237, 'changeid_42': 4238,
> 'changeid_49': 4231, 'changeid_48': 4232, 'changeid_4': 4276, 'changeid_5':
> 4275, 'changeid_6': 4274, 'changeid_7': 4273, 'changeid_1': 4279,
> 'changeid_2': 4278, 'changeid_3': 4277, 'changeid_8': 4272, 'changeid_9':
> 4271, 'changeid_58': 4222, 'changeid_59': 4221, 'changeid_52': 4228,
> 'changeid_53': 4227, 'changeid_50': 4230, 'changeid_51': 4229,
> 'changeid_56': 4224, 'changeid_57': 4223, 'changeid_54': 4226,
> 'changeid_55': 4225}
>
> We did have the UI master get stopped again for being OOM, somewhere north
> of 50G. It's currently 46.8, and been running only a couple days. My plan,
> when I get time, is to use some stuff we have in our own product based on
> guppy to see what's going on in memory, but attaching gdb to it and using
> PyRun_SimpleString() to run the heap checking stuff. But for the time
> being, I can keep restarting things.
>
> My gut feeling is that I'm going to have to shut everything down and start
> with a clean database.
>
> Neil Gilmore
> raito at raito.com
>
>
> On 8/10/2017 3:39 PM, Pierre Tardy wrote:
>
> Mmh.. sounds like you found a memory leak in the UI.
>
> Several points to check that could be out of control for UI:
> Message could be queuing up over hanged (or badly closed) websockets
> REST queries data could keep some reference in some way, which would make
> them just accumulate in memory.
> sombody is doing huge REST apis queries. It is unfortunatly quite easy to
> just hit /api/v2/builds, and dump the whole build db.
> This wouldn't go all the way to 45GB IMO.
>
> During my perf tests, I saw the logs system are quite memory hungry, and
> its buildbot is trading memory for cpu if the master can't keepup recording
> all the logs in the data (nothing fancy. the twisted queues will just be
> growing waiting for callbacks to be called).
> Due to several encoding and decoding, the memory usage in the log queue
> could be 2-4 times the amount of actual log bytes processed. anyway, this
> is probably not your problem.
>
> You can look at https://github.com/tardyp/buildbot_profiler maybe improve
> it to add a memory profiler..
>
>
> Pierre
>
>
> Le jeu. 10 août 2017 à 21:52, Neil Gilmore <ngilmore at grammatech.com> a
> écrit :
>
>> Hi all,
>>
>> A couple of times in the last couple weeks, the master running our UI
>> has crashed/exited/ceased to run. This most recent time it was a
>> MemoryError, backed up by the kernel log saying it was OOM. Current run
>> shows it using 43.1G memory. Seems like a lot, doesn't it? The other 2
>> larger masters (the ones actually running builds) are about 2G, and the
>> remaining, smallest one is about 1.7G.
>>
>> What does the UI hold onto that makes it so large?
>>
>> I'm supposed to get some heap profiling thingy wedged into buildbot so I
>> can try to figure it out. My current plan is to introduce a new build
>> step (like our current custom ones) that triggers the profiling process,
>> create a sort of dummy build using the step, and create a force
>> scheduler to trigger that build. That'll keep it on our UI master
>> anyway. Is there a better way to trigger such code in the master at
>> arbitrary times?
>>
>> I'm also starting to get complaints (and I've noticed this myself), that
>> sometimes queued builds take a long time to start after the previous
>> build finishes. Sometimes on the order of a half-hour or more. Or at
>> least it appears so. I'm going on what the UI tells me. I haven't tried
>> delving into the logs of the master controlling the builds to match up
>> times. Any ideas? I'm afraid I'm not up on exactly how/when builds are
>> supposed to get started.
>>
>> And out database seems to be accumulating integrity errors again.
>>
>> Neil Gilmore
>> raito at raito.com
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