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Sidekiq MemoryKiller

The GitLab Rails application code suffers from memory leaks. For web requests this problem is made manageable using puma-worker-killer which restarts Puma worker processes if it exceeds a memory limit. The Sidekiq MemoryKiller applies the same approach to the Sidekiq processes used by GitLab to process background jobs.

Unlike puma-worker-killer, which is enabled by default for all GitLab installations of GitLab 13.0 and later, the Sidekiq MemoryKiller is enabled by default only for Omnibus packages. The reason for this is that the MemoryKiller relies on runit to restart Sidekiq after a memory-induced shutdown and GitLab installations from source do not all use runit or an equivalent.

With the default settings, the MemoryKiller causes a Sidekiq restart no more often than once every 15 minutes, with the restart causing about one minute of delay for incoming background jobs.

Some background jobs rely on long-running external processes. To ensure these are cleanly terminated when Sidekiq is restarted, each Sidekiq process should be run as a process group leader (for example, using chpst -P). If using Omnibus or the bin/background_jobs script with runit installed, this is handled for you.

Configuring the MemoryKiller

The MemoryKiller is controlled using environment variables.

  • SIDEKIQ_DAEMON_MEMORY_KILLER: defaults to 1. When set to 0, the MemoryKiller works in legacy mode. Otherwise, the MemoryKiller works in daemon mode.

    In legacy mode, the MemoryKiller checks the Sidekiq process RSS (Resident Set Size) after each job.

    In daemon mode, the MemoryKiller checks the Sidekiq process RSS every 3 seconds (defined by SIDEKIQ_MEMORY_KILLER_CHECK_INTERVAL).

  • SIDEKIQ_MEMORY_KILLER_MAX_RSS (KB): if this variable is set, and its value is greater than 0, the MemoryKiller is enabled. Otherwise the MemoryKiller is disabled.

    SIDEKIQ_MEMORY_KILLER_MAX_RSS defines the Sidekiq process allowed RSS.

    In legacy mode, if the Sidekiq process exceeds the allowed RSS then an irreversible delayed graceful restart is triggered. The restart of Sidekiq happens after SIDEKIQ_MEMORY_KILLER_GRACE_TIME seconds.

    In daemon mode, if the Sidekiq process exceeds the allowed RSS for longer than SIDEKIQ_MEMORY_KILLER_GRACE_TIME the graceful restart is triggered. If the Sidekiq process go below the allowed RSS within SIDEKIQ_MEMORY_KILLER_GRACE_TIME, the restart is aborted.

    The default value for Omnibus packages is set in the Omnibus GitLab repository.

  • SIDEKIQ_MEMORY_KILLER_HARD_LIMIT_RSS (KB): is used by daemon mode. If the Sidekiq process RSS (expressed in kilobytes) exceeds SIDEKIQ_MEMORY_KILLER_HARD_LIMIT_RSS, an immediate graceful restart of Sidekiq is triggered.

  • SIDEKIQ_MEMORY_KILLER_CHECK_INTERVAL: used in daemon mode to define how often to check process RSS, default to 3 seconds.

  • SIDEKIQ_MEMORY_KILLER_GRACE_TIME: defaults to 900 seconds (15 minutes). The usage of this variable is described as part of SIDEKIQ_MEMORY_KILLER_MAX_RSS.

  • SIDEKIQ_MEMORY_KILLER_SHUTDOWN_WAIT: defaults to 30 seconds. This defines the maximum time allowed for all Sidekiq jobs to finish. No new jobs are accepted during that time, and the process exits as soon as all jobs finish.

    If jobs do not finish during that time, the MemoryKiller interrupts all currently running jobs by sending SIGTERM to the Sidekiq process.

    If the process hard shutdown/restart is not performed by Sidekiq, the Sidekiq process is forcefully terminated after Sidekiq.options[:timeout] + 2 seconds. An external supervision mechanism (for example, runit) must restart Sidekiq afterwards.