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diff --git a/doc/administration/sidekiq/sidekiq_troubleshooting.md b/doc/administration/sidekiq/sidekiq_troubleshooting.md new file mode 100644 index 00000000000..9bc8e473409 --- /dev/null +++ b/doc/administration/sidekiq/sidekiq_troubleshooting.md @@ -0,0 +1,381 @@ +--- +stage: Systems +group: Distribution +info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments +--- + +# Troubleshooting Sidekiq **(FREE SELF)** + +Sidekiq is the background job processor GitLab uses to asynchronously run +tasks. When things go wrong it can be difficult to troubleshoot. These +situations also tend to be high-pressure because a production system job queue +may be filling up. Users will notice when this happens because new branches +may not show up and merge requests may not be updated. The following are some +troubleshooting steps to help you diagnose the bottleneck. + +GitLab administrators/users should consider working through these +debug steps with GitLab Support so the backtraces can be analyzed by our team. +It may reveal a bug or necessary improvement in GitLab. + +In any of the backtraces, be wary of suspecting cases where every +thread appears to be waiting in the database, Redis, or waiting to acquire +a mutex. This **may** mean there's contention in the database, for example, +but look for one thread that is different than the rest. This other thread +may be using all available CPU, or have a Ruby Global Interpreter Lock, +preventing other threads from continuing. + +## Log arguments to Sidekiq jobs + +[In GitLab 13.6 and later](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/44853) +some arguments passed to Sidekiq jobs are logged by default. +To avoid logging sensitive information (for instance, password reset tokens), +GitLab logs numeric arguments for all workers, with overrides for some specific +workers where their arguments are not sensitive. + +Example log output: + +```json +{"severity":"INFO","time":"2020-06-08T14:37:37.892Z","class":"AdminEmailsWorker","args":["[FILTERED]","[FILTERED]","[FILTERED]"],"retry":3,"queue":"admin_emails","backtrace":true,"jid":"9e35e2674ac7b12d123e13cc","created_at":"2020-06-08T14:37:37.373Z","meta.user":"root","meta.caller_id":"Admin::EmailsController#create","correlation_id":"37D3lArJmT1","uber-trace-id":"2d942cc98cc1b561:6dc94409cfdd4d77:9fbe19bdee865293:1","enqueued_at":"2020-06-08T14:37:37.410Z","pid":65011,"message":"AdminEmailsWorker JID-9e35e2674ac7b12d123e13cc: done: 0.48085 sec","job_status":"done","scheduling_latency_s":0.001012,"redis_calls":9,"redis_duration_s":0.004608,"redis_read_bytes":696,"redis_write_bytes":6141,"duration_s":0.48085,"cpu_s":0.308849,"completed_at":"2020-06-08T14:37:37.892Z","db_duration_s":0.010742} +{"severity":"INFO","time":"2020-06-08T14:37:37.894Z","class":"ActiveJob::QueueAdapters::SidekiqAdapter::JobWrapper","wrapped":"ActionMailer::MailDeliveryJob","queue":"mailers","args":["[FILTERED]"],"retry":3,"backtrace":true,"jid":"e47a4f6793d475378432e3c8","created_at":"2020-06-08T14:37:37.884Z","meta.user":"root","meta.caller_id":"AdminEmailsWorker","correlation_id":"37D3lArJmT1","uber-trace-id":"2d942cc98cc1b561:29344de0f966446d:5c3b0e0e1bef987b:1","enqueued_at":"2020-06-08T14:37:37.885Z","pid":65011,"message":"ActiveJob::QueueAdapters::SidekiqAdapter::JobWrapper JID-e47a4f6793d475378432e3c8: start","job_status":"start","scheduling_latency_s":0.009473} +{"severity":"INFO","time":"2020-06-08T14:39:50.648Z","class":"NewIssueWorker","args":["455","1"],"retry":3,"queue":"new_issue","backtrace":true,"jid":"a24af71f96fd129ec47f5d1e","created_at":"2020-06-08T14:39:50.643Z","meta.user":"root","meta.project":"h5bp/html5-boilerplate","meta.root_namespace":"h5bp","meta.caller_id":"Projects::IssuesController#create","correlation_id":"f9UCZHqhuP7","uber-trace-id":"28f65730f99f55a3:a5d2b62dec38dffc:48ddd092707fa1b7:1","enqueued_at":"2020-06-08T14:39:50.646Z","pid":65011,"message":"NewIssueWorker JID-a24af71f96fd129ec47f5d1e: start","job_status":"start","scheduling_latency_s":0.001144} +``` + +When using [Sidekiq JSON logging](../logs/index.md#sidekiqlog), +arguments logs are limited to a maximum size of 10 kilobytes of text; +any arguments after this limit are discarded and replaced with a +single argument containing the string `"..."`. + +You can set `SIDEKIQ_LOG_ARGUMENTS` [environment variable](https://docs.gitlab.com/omnibus/settings/environment-variables.html) +to `0` (false) to disable argument logging. + +Example: + +```ruby +gitlab_rails['env'] = {"SIDEKIQ_LOG_ARGUMENTS" => "0"} +``` + +In GitLab 13.5 and earlier, set `SIDEKIQ_LOG_ARGUMENTS` to `1` to start logging arguments passed to Sidekiq. + +## Thread dump + +Send the Sidekiq process ID the `TTIN` signal to output thread +backtraces in the log file. + +```shell +kill -TTIN <sidekiq_pid> +``` + +Check in `/var/log/gitlab/sidekiq/current` or `$GITLAB_HOME/log/sidekiq.log` for +the backtrace output. The backtraces are lengthy and generally start with +several `WARN` level messages. Here's an example of a single thread's backtrace: + +```plaintext +2016-04-13T06:21:20.022Z 31517 TID-orn4urby0 WARN: ActiveRecord::RecordNotFound: Couldn't find Note with 'id'=3375386 +2016-04-13T06:21:20.022Z 31517 TID-orn4urby0 WARN: /opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.5.2/lib/active_record/core.rb:155:in `find' +/opt/gitlab/embedded/service/gitlab-rails/app/workers/new_note_worker.rb:7:in `perform' +/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/sidekiq-4.0.1/lib/sidekiq/processor.rb:150:in `execute_job' +/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/sidekiq-4.0.1/lib/sidekiq/processor.rb:132:in `block (2 levels) in process' +/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/sidekiq-4.0.1/lib/sidekiq/middleware/chain.rb:127:in `block in invoke' +/opt/gitlab/embedded/service/gitlab-rails/lib/gitlab/sidekiq_middleware/memory_killer.rb:17:in `call' +/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/sidekiq-4.0.1/lib/sidekiq/middleware/chain.rb:129:in `block in invoke' +/opt/gitlab/embedded/service/gitlab-rails/lib/gitlab/sidekiq_middleware/arguments_logger.rb:6:in `call' +... +``` + +In some cases Sidekiq may be hung and unable to respond to the `TTIN` signal. +Move on to other troubleshooting methods if this happens. + +## Ruby profiling with `rbspy` + +[rbspy](https://rbspy.github.io) is an easy to use and low-overhead Ruby profiler that can be used to create +flamegraph-style diagrams of CPU usage by Ruby processes. + +No changes to GitLab are required to use it and it has no dependencies. To install it: + +1. Download the binary from the [`rbspy` releases page](https://github.com/rbspy/rbspy/releases). +1. Make the binary executable. + +To profile a Sidekiq worker for one minute, run: + +```shell +sudo ./rbspy record --pid <sidekiq_pid> --duration 60 --file /tmp/sidekiq_profile.svg +``` + + + +In this example of a flamegraph generated by `rbspy`, almost all of the Sidekiq process's time is spent in `rev_parse`, a native C +function in Rugged. In the stack, we can see `rev_parse` is being called by the `ExpirePipelineCacheWorker`. + +## Process profiling with `perf` + +Linux has a process profiling tool called `perf` that is helpful when a certain +process is eating up a lot of CPU. If you see high CPU usage and Sidekiq isn't +responding to the `TTIN` signal, this is a good next step. + +If `perf` is not installed on your system, install it with `apt-get` or `yum`: + +```shell +# Debian +sudo apt-get install linux-tools + +# Ubuntu (may require these additional Kernel packages) +sudo apt-get install linux-tools-common linux-tools-generic linux-tools-`uname -r` + +# Red Hat/CentOS +sudo yum install perf +``` + +Run `perf` against the Sidekiq PID: + +```shell +sudo perf record -p <sidekiq_pid> +``` + +Let this run for 30-60 seconds and then press Ctrl-C. Then view the `perf` report: + +```shell +$ sudo perf report + +# Sample output +Samples: 348K of event 'cycles', Event count (approx.): 280908431073 + 97.69% ruby nokogiri.so [.] xmlXPathNodeSetMergeAndClear + 0.18% ruby libruby.so.2.1.0 [.] objspace_malloc_increase + 0.12% ruby libc-2.12.so [.] _int_malloc + 0.10% ruby libc-2.12.so [.] _int_free +``` + +Above you see sample output from a `perf` report. It shows that 97% of the CPU is +being spent inside Nokogiri and `xmlXPathNodeSetMergeAndClear`. For something +this obvious you should then go investigate what job in GitLab would use +Nokogiri and XPath. Combine with `TTIN` or `gdb` output to show the +corresponding Ruby code where this is happening. + +## The GNU Project Debugger (`gdb`) + +`gdb` can be another effective tool for debugging Sidekiq. It gives you a little +more interactive way to look at each thread and see what's causing problems. + +Attaching to a process with `gdb` suspends the normal operation +of the process (Sidekiq does not process jobs while `gdb` is attached). + +Start by attaching to the Sidekiq PID: + +```shell +gdb -p <sidekiq_pid> +``` + +Then gather information on all the threads: + +```plaintext +info threads + +# Example output +30 Thread 0x7fe5fbd63700 (LWP 26060) 0x0000003f7cadf113 in poll () from /lib64/libc.so.6 +29 Thread 0x7fe5f2b3b700 (LWP 26533) 0x0000003f7ce0b68c in pthread_cond_wait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0 +28 Thread 0x7fe5f2a3a700 (LWP 26534) 0x0000003f7ce0ba5e in pthread_cond_timedwait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0 +27 Thread 0x7fe5f2939700 (LWP 26535) 0x0000003f7ce0b68c in pthread_cond_wait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0 +26 Thread 0x7fe5f2838700 (LWP 26537) 0x0000003f7ce0b68c in pthread_cond_wait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0 +25 Thread 0x7fe5f2737700 (LWP 26538) 0x0000003f7ce0b68c in pthread_cond_wait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0 +24 Thread 0x7fe5f2535700 (LWP 26540) 0x0000003f7ce0b68c in pthread_cond_wait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0 +23 Thread 0x7fe5f2434700 (LWP 26541) 0x0000003f7ce0b68c in pthread_cond_wait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0 +22 Thread 0x7fe5f2232700 (LWP 26543) 0x0000003f7ce0b68c in pthread_cond_wait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0 +21 Thread 0x7fe5f2131700 (LWP 26544) 0x00007fe5f7b570f0 in xmlXPathNodeSetMergeAndClear () +from /opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/nokogiri-1.6.7.2/lib/nokogiri/nokogiri.so +... +``` + +If you see a suspicious thread, like the Nokogiri one above, you may want +to get more information: + +```plaintext +thread 21 +bt + +# Example output +#0 0x00007ff0d6afe111 in xmlXPathNodeSetMergeAndClear () from /opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/nokogiri-1.6.7.2/lib/nokogiri/nokogiri.so +#1 0x00007ff0d6b0b836 in xmlXPathNodeCollectAndTest () from /opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/nokogiri-1.6.7.2/lib/nokogiri/nokogiri.so +#2 0x00007ff0d6b09037 in xmlXPathCompOpEval () from /opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/nokogiri-1.6.7.2/lib/nokogiri/nokogiri.so +#3 0x00007ff0d6b09017 in xmlXPathCompOpEval () from /opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/nokogiri-1.6.7.2/lib/nokogiri/nokogiri.so +#4 0x00007ff0d6b092e0 in xmlXPathCompOpEval () from /opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/nokogiri-1.6.7.2/lib/nokogiri/nokogiri.so +#5 0x00007ff0d6b0bc37 in xmlXPathRunEval () from /opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/nokogiri-1.6.7.2/lib/nokogiri/nokogiri.so +#6 0x00007ff0d6b0be5f in xmlXPathEvalExpression () from /opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/nokogiri-1.6.7.2/lib/nokogiri/nokogiri.so +#7 0x00007ff0d6a97dc3 in evaluate (argc=2, argv=0x1022d058, self=<value optimized out>) at xml_xpath_context.c:221 +#8 0x00007ff0daeab0ea in vm_call_cfunc_with_frame (th=0x1022a4f0, reg_cfp=0x1032b810, ci=<value optimized out>) at vm_insnhelper.c:1510 +``` + +To output a backtrace from all threads at once: + +```plaintext +set pagination off +thread apply all bt +``` + +Once you're done debugging with `gdb`, be sure to detach from the process and +exit: + +```plaintext +detach +exit +``` + +## Sidekiq kill signals + +TTIN was described above as the signal to print backtraces for logging, however +Sidekiq responds to other signals as well. For example, TSTP and TERM can be used +to gracefully shut Sidekiq down, see +[the Sidekiq Signals docs](https://github.com/mperham/sidekiq/wiki/Signals#ttin). + +## Check for blocking queries + +Sometimes the speed at which Sidekiq processes jobs can be so fast that it can +cause database contention. Check for blocking queries when backtraces above +show that many threads are stuck in the database adapter. + +The PostgreSQL wiki has details on the query you can run to see blocking +queries. The query is different based on PostgreSQL version. See +[Lock Monitoring](https://wiki.postgresql.org/wiki/Lock_Monitoring) for +the query details. + +## Managing Sidekiq queues + +It is possible to use [Sidekiq API](https://github.com/mperham/sidekiq/wiki/API) +to perform a number of troubleshooting steps on Sidekiq. + +These are the administrative commands and it should only be used if currently +administration interface is not suitable due to scale of installation. + +All these commands should be run using `gitlab-rails console`. + +### View the queue size + +```ruby +Sidekiq::Queue.new("pipeline_processing:build_queue").size +``` + +### Enumerate all enqueued jobs + +```ruby +queue = Sidekiq::Queue.new("chaos:chaos_sleep") +queue.each do |job| + # job.klass # => 'MyWorker' + # job.args # => [1, 2, 3] + # job.jid # => jid + # job.queue # => chaos:chaos_sleep + # job["retry"] # => 3 + # job.item # => { + # "class"=>"Chaos::SleepWorker", + # "args"=>[1000], + # "retry"=>3, + # "queue"=>"chaos:chaos_sleep", + # "backtrace"=>true, + # "queue_namespace"=>"chaos", + # "jid"=>"39bc482b823cceaf07213523", + # "created_at"=>1566317076.266069, + # "correlation_id"=>"c323b832-a857-4858-b695-672de6f0e1af", + # "enqueued_at"=>1566317076.26761}, + # } + + # job.delete if job.jid == 'abcdef1234567890' +end +``` + +### Enumerate currently running jobs + +```ruby +workers = Sidekiq::Workers.new +workers.each do |process_id, thread_id, work| + # process_id is a unique identifier per Sidekiq process + # thread_id is a unique identifier per thread + # work is a Hash which looks like: + # {"queue"=>"chaos:chaos_sleep", + # "payload"=> + # { "class"=>"Chaos::SleepWorker", + # "args"=>[1000], + # "retry"=>3, + # "queue"=>"chaos:chaos_sleep", + # "backtrace"=>true, + # "queue_namespace"=>"chaos", + # "jid"=>"b2a31e3eac7b1a99ff235869", + # "created_at"=>1566316974.9215662, + # "correlation_id"=>"e484fb26-7576-45f9-bf21-b99389e1c53c", + # "enqueued_at"=>1566316974.9229589}, + # "run_at"=>1566316974}], +end +``` + +### Remove Sidekiq jobs for given parameters (destructive) + +The general method to kill jobs conditionally is the following command, which +removes jobs that are queued but not started. Running jobs can not be killed. + +```ruby +queue = Sidekiq::Queue.new('<queue name>') +queue.each { |job| job.delete if <condition>} +``` + +Have a look at the section below for cancelling running jobs. + +In the method above, `<queue-name>` is the name of the queue that contains the jobs you want to delete and `<condition>` decides which jobs get deleted. + +Commonly, `<condition>` references the job arguments, which depend on the type of job in question. To find the arguments for a specific queue, you can have a look at the `perform` function of the related worker file, commonly found at `/app/workers/<queue-name>_worker.rb`. + +For example, `repository_import` has `project_id` as the job argument, while `update_merge_requests` has `project_id, user_id, oldrev, newrev, ref`. + +Arguments need to be referenced by their sequence ID using `job.args[<id>]` because `job.args` is a list of all arguments provided to the Sidekiq job. + +Here are some examples: + +```ruby +queue = Sidekiq::Queue.new('update_merge_requests') +# In this example, we want to remove any update_merge_requests jobs +# for the Project with ID 125 and ref `ref/heads/my_branch` +queue.each { |job| job.delete if job.args[0] == 125 and job.args[4] == 'ref/heads/my_branch' } +``` + +```ruby +# Cancelling jobs like: `RepositoryImportWorker.new.perform_async(100)` +id_list = [100] + +queue = Sidekiq::Queue.new('repository_import') +queue.each do |job| + job.delete if id_list.include?(job.args[0]) +end +``` + +### Remove specific job ID (destructive) + +```ruby +queue = Sidekiq::Queue.new('repository_import') +queue.each do |job| + job.delete if job.jid == 'my-job-id' +end +``` + +## Canceling running jobs (destructive) + +> Introduced in GitLab 12.3. + +This is highly risky operation and use it as last resort. +Doing that might result in data corruption, as the job +is interrupted mid-execution and it is not guaranteed +that proper rollback of transactions is implemented. + +```ruby +Gitlab::SidekiqDaemon::Monitor.cancel_job('job-id') +``` + +> This requires the Sidekiq to be run with `SIDEKIQ_MONITOR_WORKER=1` +> environment variable. + +To perform of the interrupt we use `Thread.raise` which +has number of drawbacks, as mentioned in [Why Ruby's Timeout is dangerous (and Thread.raise is terrifying)](https://jvns.ca/blog/2015/11/27/why-rubys-timeout-is-dangerous-and-thread-dot-raise-is-terrifying/): + +> This is where the implications get interesting, and terrifying. This means that an exception can get raised: +> +> - during a network request (ok, as long as the surrounding code is prepared to catch Timeout::Error) +> - during the cleanup for the network request +> - during a rescue block +> - while creating an object to save to the database afterwards +> - in any of your code, regardless of whether it could have possibly raised an exception before +> +> Nobody writes code to defend against an exception being raised on literally any line. That's not even possible. So Thread.raise is basically like a sneak attack on your code that could result in almost anything. It would probably be okay if it were pure-functional code that did not modify any state. But this is Ruby, so that's unlikely :) |