I did try to do that! I have 3 heap profiles captured from the ~3 seconds
before crash. The only thing particularly suspicious is the httptrace call
I mentioned earlier in the thread.
Diffing 1 to 2
(pprof) cum
(pprof) top 50
Showing nodes accounting for 4604.15kB, 81.69% of 5636.17kB total
flat flat% sum% cum cum%
0 0% 0% 5120.16kB 90.84%
net/http/httptrace.(*ClientTrace).compose.func1
0 0% 0% 5120.16kB 90.84% reflect.Value.Call
0 0% 0% 5120.16kB 90.84% reflect.Value.call
0 0% 0% 5120.16kB 90.84% reflect.callReflect
5120.16kB 90.84% 90.84% 5120.16kB 90.84% reflect.funcLayout.func1
0 0% 90.84% 5120.16kB 90.84% reflect.makeFuncStub
0 0% 90.84% 4604.15kB 81.69% sync.(*Pool).Get
0 0% 90.84% -516.01kB 9.16% io.Copy
0 0% 90.84% -516.01kB 9.16% io.copyBuffer
0 0% 90.84% -516.01kB 9.16% io/ioutil.devNull.ReadFrom
-516.01kB 9.16% 81.69% -516.01kB 9.16% io/ioutil.glob..func1
Diff 2 to 3
(pprof) top 50
Showing nodes accounting for 7680.44kB, 100% of 7680.44kB total
flat flat% sum% cum cum%
0 0% 0% 6144.18kB 80.00%
net/http/httptrace.(*ClientTrace).compose.func1
0 0% 0% 6144.18kB 80.00% reflect.Value.Call
0 0% 0% 6144.18kB 80.00% reflect.Value.call
512.01kB 6.67% 6.67% 6144.18kB 80.00% reflect.callReflect
0 0% 6.67% 6144.18kB 80.00% reflect.makeFuncStub
5632.17kB 73.33% 80.00% 5632.17kB 73.33% reflect.funcLayout.func1
0 0% 80.00% 5632.17kB 73.33% sync.(*Pool).Get
0 0% 80.00% 1024.23kB 13.34%
github.com/aws/aws-sdk-go/aws/request.(*HandlerList).Run
0 0% 80.00% 1024.23kB 13.34%
github.com/aws/aws-sdk-go/aws/request.(*Request).Send
0 0% 80.00% 1024.23kB 13.34%
github.com/aws/aws-sdk-go/aws/request.(*Request).Sign
0 0% 80.00% 1024.23kB 13.34%
github.com/aws/aws-sdk-go/aws/signer/v4.(*signingCtx).build
0 0% 80.00% 1024.23kB 13.34%
github.com/aws/aws-sdk-go/aws/signer/v4.SignSDKRequest
0 0% 80.00% 1024.23kB 13.34%
github.com/aws/aws-sdk-go/aws/signer/v4.SignSDKRequestWithCurrentTime
0 0% 80.00% 1024.23kB 13.34%
github.com/aws/aws-sdk-go/aws/signer/v4.Signer.signWithBody
0 0% 80.00% 1024.23kB 13.34%
github.com/aws/aws-sdk-go/service/dynamodb.(*DynamoDB).GetItemWithContext
On Tue, Jul 2, 2019 at 2:08 PM andrey mirtchovski <mirtchov...@gmail.com>
wrote:
> What I have found useful in the past is pprof's ability to diff profiles.
> That means that if you capture heap profiles at regular intervals you can
> see a much smaller subset of changes and compare allocation patterns.
>
> On Tue, Jul 2, 2019, 10:53 AM 'Yunchi Luo' via golang-nuts <
> golang-nuts@googlegroups.com> wrote:
>
>> I'm not so much pointing my finger at GC as I am hoping GC logs could
>> help tell the story, and that someone with a strong understanding of GC in
>> Go could weigh in here. In the last 4 seconds before OOM, "TotalAlloc"
>> increased by only 80M, yet "HeapIdle" increased to 240M from 50M, RSS
>> increased by 810M. The numbers don't add up for me. A running sum of 80M of
>> heap objects were allocated in the time RSS increased by 10X that. If GC
>> was completely off, I still wouldn't expect this to happen, which makes me
>> want to rule out GC being blocked as a problem. Maybe there was runaway
>> heap reservation because something in my code caused a ton of
>> fragmentation? Is that sane? The heap profile lacking clues is also strange.
>>
>> Regarding the possibility of a race, I forgot I do have goroutine
>> profiles captured along with the heap profiles at the time memory exploded.
>> There are only 10 goroutines running on the serving path, which rules out
>> too many concurrent requests being served (please correct me if I'm wrong).
>> Those fan out to 13 goroutines talking to the db, all of which are in
>> http.Transport.roundTrip (which is blocked on runtime.gopark so I assume
>> they are waiting on the TCP connection). All other goroutines that don't
>> originate in the stdlib are also blocked on `select` or sleeping. Our CI
>> does run with go test -race, but I'll try doing some load testing with a
>> race detector enabled binary.
>>
>> Bakul, that is sound advice. I've actually been debugging this on and off
>> for a couple months now, with the help of several people, a few of which
>> have peer reviewed the code. I agree it's most likely to be some runaway
>> code that I caused in my logic, but we haven't been able to pin-point the
>> cause and I've run out of hypothesis to test at the moment. This is why
>> I've started asking on go-nuts@. The circuit breaker code was one of the
>> first things I checked, has been unit tested and verified working with load
>> tests. Now that you mention it, I actually did uncover a Go stdlib bug in
>> http2 while doing the load tests... but that's unrelated.
>>
>>
>> On Tue, Jul 2, 2019 at 2:24 AM Bakul Shah <ba...@bitblocks.com> wrote:
>>
>>> Before assuming it is the GC or something system related, you may wish
>>> to verify it is *not your own logic*. Larger RSS could also be due to your
>>> own logic touching more and more memory due to some runaway effect. The
>>> probability this has to do with GC is very low given the very widespread
>>> use of Go and the probability of a bug in new code is very high given it is
>>> used on a much much smaller scale.
>>>
>>> This has the "smell" of a concurrency bug. If I were you I'd test the
>>> code for any races, I'd review the code thoroughly with someone who doesn't
>>> know the code so that I'm forced to explain it, and I'd add plenty of
>>> assertions. I'd probably first look at the circuit breaker code -- things
>>> like how does it know how many concurrent connections exist?
>>>
>>> In general, any hypothesis you come up with, you should have a test that
>>> *catches* the bug given the hypothesis. Elusive bugs tend to become more
>>> elusive as you are on the hunt and as you may fix other problems you
>>> discover on the way.
>>>
>>> I even suspect you're looking at GC logs a bit too early. Instrument
>>> your own code and look at what patterns emerge. [Not to mention any time
>>> you spend on understanding your code will help improve your service; but
>>> better understanding of and debugging the GC won't necessarily help you!]
>>>
>>> On Jul 1, 2019, at 12:14 PM, 'Yunchi Luo' via golang-nuts <
>>> golang-nuts@googlegroups.com> wrote:
>>>
>>> Hello, I'd like to solicit some help with a weird GC issue we are seeing.
>>>
>>> I'm trying to debug OOM on a service we are running in k8s. The service
>>> is just a CRUD server hitting a database (DynamoDB). Each replica serves
>>> about 300 qps of traffic. There are no memory leaks. On occasion (seemingly
>>> correlated to small latency spikes on the backend), the service would OOM.
>>> This is surprising because it has a circuit breaker that drops requests
>>> after 200 concurrent connections that has never trips, and goroutine
>>> profiles confirm that there are nowhere 200 active goroutines.
>>>
>>> GC logs are pasted below. It's interlaced with dumps of runtime.Memstats
>>> (the RSS number is coming from /proc/<pid>/stats). Go version is 1.12.5,
>>> running an Alpine 3.10 container in an Amazon kernel
>>> 4.14.123-111.109.amzn2.x86_64.
>>>
>>> The service happily serves requests using ~50MB of RSS for hours, until
>>> the last 2 seconds, where GC mark&sweep time starts to 2-4X per cycle
>>> (43+489/158/0.60+0.021
>>> ms cpu => 43+489/158/0.60+0.021 ms cpu), and RSS and Sys blow up. It’s
>>> also interesting that in the last log line: `Sys=995MB RSS=861MB
>>> HeapSys=199MB`. If I’m reading this correctly, there’s at least `662MB` of
>>> memory in RSS that is not assigned to the heap. Though this might be due to
>>> the change in 1.125 to use MADV_FREE, so the pages are freeable not yet
>>> reclaimed by the kernel.
>>>
>>> I don’t understand how heap can be so small across gc cycles
>>> (28->42->30MB on the last line means heap doesn't grow past 42MB?), yet RSS
>>> keeps growing. I'm assuming the increased RSS is causing the kernel to OOM
>>> the service, but that should only happen if the RSS is not freeable as
>>> marked by MADV_FREE. There doesn't seem to be any indication of that from
>>> the GC logs. I guess this all comes down to me not having a good
>>> understanding of how the GC algorithm works and how to read these logs. I'd
>>> really appreciate it if anyone can explain what's happening and why.
>>>
>>> gc 41833 @19135.227s 0%: 0.019+2.3+0.005 ms clock,
>>> 0.079+0.29/2.2/5.6+0.020 ms cpu, 11->11->5 MB, 12 MB goal, 4 P
>>> INFO 2019-06-30T08:46:04.886 [Memory]: Alloc=7MB TotalAlloc=230172MB
>>> Sys=69MB RSS=51MB HeapSys=62MB HeapIdle=51MB HeapInUse=11MB HeapReleased=5MB
>>> gc 41834 @19135.869s 0%: 0.005+2.9+0.003 ms clock,
>>> 0.023+0.32/2.5/6.6+0.012 ms cpu, 11->11->5 MB, 12 MB goal, 4 P
>>> INFO 2019-06-30T08:46:05.886 [Memory]: Alloc=9MB TotalAlloc=230179MB
>>> Sys=69MB RSS=51MB HeapSys=62MB HeapIdle=50MB HeapInUse=12MB HeapReleased=5MB
>>> gc 41835 @19136.704s 0%: 0.038+2.1+0.004 ms clock,
>>> 0.15+0.35/2.1/5.3+0.016 ms cpu, 11->11->5 MB, 12 MB goal, 4 P
>>> INFO 2019-06-30T08:46:06.886 [Memory]: Alloc=9MB TotalAlloc=230184MB
>>> Sys=69MB RSS=51MB HeapSys=62MB HeapIdle=50MB HeapInUse=12MB HeapReleased=5MB
>>> gc 41836 @19137.611s 0%: 0.009+2.1+0.003 ms clock,
>>> 0.036+0.39/2.0/5.7+0.015 ms cpu, 11->11->5 MB, 12 MB goal, 4 P
>>> INFO 2019-06-30T08:46:07.887 [Memory]: Alloc=10MB TotalAlloc=230190MB
>>> Sys=69MB RSS=51MB HeapSys=62MB HeapIdle=49MB HeapInUse=12MB HeapReleased=5MB
>>> gc 41837 @19138.444s 0%: 0.008+2.1+0.004 ms clock,
>>> 0.035+0.51/2.1/5.7+0.017 ms cpu, 11->11->5 MB, 12 MB goal, 4 P
>>> INFO 2019-06-30T08:46:08.887 [Memory]: Alloc=10MB TotalAlloc=230195MB
>>> Sys=69MB RSS=51MB HeapSys=62MB HeapIdle=49MB HeapInUse=12MB HeapReleased=5MB
>>> gc 41838 @19139.474s 0%: 0.005+2.6+0.003 ms clock,
>>> 0.023+0.37/2.5/4.3+0.014 ms cpu, 11->11->5 MB, 12 MB goal, 4 P
>>> gc 41839 @19140.173s 0%: 0.011+2.4+0.003 ms clock,
>>> 0.046+0.20/2.3/5.8+0.015 ms cpu, 11->11->5 MB, 12 MB goal, 4 P
>>> INFO 2019-06-30T08:46:09.887 [Memory]: Alloc=7MB TotalAlloc=230202MB
>>> Sys=69MB RSS=51MB HeapSys=62MB HeapIdle=50MB HeapInUse=11MB HeapReleased=5MB
>>> gc 41840 @19140.831s 0%: 0.082+2.1+0.003 ms clock,
>>> 0.32+0.64/2.1/5.3+0.014 ms cpu, 11->11->5 MB, 12 MB goal, 4 P
>>> INFO 2019-06-30T08:46:10.887 [Memory]: Alloc=9MB TotalAlloc=230209MB
>>> Sys=69MB RSS=51MB HeapSys=62MB HeapIdle=50MB HeapInUse=12MB HeapReleased=5MB
>>> gc 41841 @19141.655s 0%: 0.014+2.1+0.003 ms clock,
>>> 0.056+0.28/2.0/5.7+0.013 ms cpu, 11->11->5 MB, 12 MB goal, 4 P
>>> gc 41842 @19142.316s 0%: 0.006+2.7+0.003 ms clock,
>>> 0.027+0.29/2.6/6.2+0.014 ms cpu, 11->11->5 MB, 12 MB goal, 4 P
>>> INFO 2019-06-30T08:46:11.888 [Memory]: Alloc=6MB TotalAlloc=230216MB
>>> Sys=69MB RSS=51MB HeapSys=62MB HeapIdle=51MB HeapInUse=11MB HeapReleased=5MB
>>> gc 41843 @19142.942s 0%: 0.010+2.1+0.005 ms clock,
>>> 0.040+0.29/2.0/5.7+0.023 ms cpu, 11->11->5 MB, 12 MB goal, 4 P
>>> INFO 2019-06-30T08:46:12.888 [Memory]: Alloc=9MB TotalAlloc=230223MB
>>> Sys=69MB RSS=51MB HeapSys=62MB HeapIdle=50MB HeapInUse=11MB HeapReleased=5MB
>>> gc 41844 @19143.724s 0%: 0.008+2.4+0.004 ms clock,
>>> 0.035+0.38/2.0/5.7+0.017 ms cpu, 11->11->5 MB, 12 MB goal, 4 P
>>> gc 41845 @19144.380s 0%: 10+9.3+0.044 ms clock, 43+6.1/9.2/4.4+0.17 ms
>>> cpu, 11->11->6 MB, 12 MB goal, 4 P
>>> INFO 2019-06-30T08:46:13.901 [Memory]: Alloc=6MB TotalAlloc=230230MB
>>> Sys=136MB RSS=98MB HeapSys=94MB HeapIdle=83MB HeapInUse=11MB
>>> HeapReleased=35MB
>>> gc 41846 @19144.447s 0%: 0.008+26+0.005 ms clock,
>>> 0.033+0.46/7.8/26+0.020 ms cpu, 11->12->9 MB, 12 MB goal, 4 P
>>> gc 41847 @19144.672s 0%: 0.013+76+0.006 ms clock,
>>> 0.053+0.20/6.4/80+0.024 ms cpu, 17->18->8 MB, 18 MB goal, 4 P
>>> gc 41848 @19145.014s 0%: 0.008+172+0.005 ms clock,
>>> 0.035+0.13/8.5/177+0.022 ms cpu, 15->17->10 MB, 16 MB goal, 4 P
>>> gc 41849 @19145.298s 0%: 0.007+285+0.006 ms clock,
>>> 0.030+10/285/7.6+0.024 ms cpu, 19->23->15 MB, 20 MB goal, 4 P
>>> INFO 2019-06-30T08:46:15.052 [Memory]: Alloc=22MB TotalAlloc=230264MB
>>> Sys=598MB RSS=531MB HeapSys=265MB HeapIdle=240MB HeapInUse=25MB
>>> HeapReleased=164MB
>>> gc 41850 @19145.665s 0%: 10+419+0.005 ms clock, 43+489/158/0.60+0.021 ms
>>> cpu, 26->30->17 MB, 30 MB goal, 4 P
>>> gc 41851 @19146.325s 0%: 21+798+0.036 ms clock, 86+990/401/0+0.14 ms
>>> cpu, 28->42->30 MB, 34 MB goal, 4 P
>>> INFO 2019-06-30T08:46:16.613 [Memory]: Alloc=41MB TotalAlloc=230303MB
>>> Sys=995MB RSS=861MB HeapSys=199MB HeapIdle=155MB HeapInUse=44MB
>>> HeapReleased=54MB
>>>
>>> I also captured the OOM log from dmesg here
>>> https://gist.github.com/mightyguava/7ecc6fc55f5cd925062d6beede3783b3.
>>>
>>> --
>>> Yunchi
>>>
>>> --
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>>>
>>>
>>
>> --
>> Yunchi
>>
>> --
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>
--
Yunchi
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