gitlab-sidekiq-fetcher

gitlab-sidekiq-fetcher is an extension to Sidekiq that adds support for reliable fetches from Redis.

It's based on https://github.com/TEA-ebook/sidekiq-reliable-fetch.

IMPORTANT NOTE: Since version 0.11.0 this gem works only with sidekiq >= 7 (which introduced Fetch API breaking changes). Please use version ~> 0.10 if you use older version of the sidekiq .

UPGRADE NOTE: If upgrading from 0.7.0, strongly consider a full deployed step on 0.7.1 before 0.8.0; that fixes a bug in the queue name validation that will hit if sidekiq nodes running 0.7.0 see working queues named by 0.8.0. See https://gitlab.com/gitlab-org/sidekiq-reliable-fetch/-/merge_requests/22

There are two strategies implemented: Reliable fetch using rpoplpush command and semi-reliable fetch that uses regular brpop and lpush to pick the job and put it to working queue. The main benefit of "Reliable" strategy is that rpoplpush is atomic, eliminating a race condition in which jobs can be lost. However, it comes at a cost because rpoplpush can't watch multiple lists at the same time so we need to iterate over the entire queue list which significantly increases pressure on Redis when there are more than a few queues. The "semi-reliable" strategy is much more reliable than the default Sidekiq fetcher, though. Compared to the reliable fetch strategy, it does not increase pressure on Redis significantly.

Interruption handling

Sidekiq expects any job to report succcess or to fail. In the last case, Sidekiq puts retry_count counter into the job and keeps to re-run the job until the counter reched the maximum allowed value. When the job has not been given a chance to finish its work(to report success or fail), for example, when it was killed forcibly or when the job was requeued, after receiving TERM signal, the standard retry mechanisme does not get into the game and the job will be retried indefinatelly. This is why Reliable fetcher maintains a special counter interrupted_count which is used to limit the amount of such retries. In both cases, Reliable Fetcher increments counter interrupted_count and rejects the job from running again when the counter exceeds max_retries_after_interruption times (default: 3 times). Such a job will be put to interrupted queue. This queue mostly behaves as Sidekiq Dead queue so it only stores a limited amount of jobs for a limited term. Same as for Dead queue, all the limits are configurable via interrupted_max_jobs (default: 10_000) and interrupted_timeout_in_seconds (default: 3 months) Sidekiq option keys.

You can also disable special handling of interrupted jobs by setting max_retries_after_interruption into -1. In this case, interrupted jobs will be run without any limits from Reliable Fetcher and they won't be put into Interrupted queue.

Installation

This gem is vendored in the GitLab Rails application and new versions are not published to RubyGems.

Configuration

Enable reliable fetches by calling this gem from your Sidekiq configuration:

Sidekiq.configure_server do |config|
  Sidekiq::ReliableFetch.setup_reliable_fetch!(config)

  # …
end

There is an additional parameter config[:semi_reliable_fetch] you can use to switch between two strategies:

Sidekiq.configure_server do |config|
  config[:semi_reliable_fetch] = true # Default value is false

  Sidekiq::ReliableFetch.setup_reliable_fetch!(config)
end

License

LGPL-3.0, see the LICENSE file.