Batch Support

[jpcamara]

Support for batches in SolidQueue!

Batches are a powerful feature in Sidekiq Pro and GoodJob which help with job coordination. A "Batch" is a collection of jobs, and when those jobs meet certain completion criteria it can optionally trigger another job with the batch record as an argument.

The goal of this feature is to:

1. Enhance job coordination
2. Maintain the overall simplicity of SolidQueue. To quote @rosa in the batch support issue:

We have batch support in our list of possible features to add, but it's not in the immediate plans because it's a bit at odds with the simplicity we're aiming for... I'm not quite sure yet how it could look like, in a way that maintains the overall simplicity of the gem

This PR provides a functional batch implementation. The following scenarios will work:

# Create a job to run as part of the batch
class SleepyJob < ApplicationJob
  queue_as :background

  def perform(seconds_to_sleep)
    Rails.logger.info "Feeling #{seconds_to_sleep} seconds sleepy..."
    sleep seconds_to_sleep
  end
end

# Create a batch completion job - the first argument is always the batch record itself
class BatchCompletionJob < ApplicationJob
  queue_as :background

  def perform(batch)
    Rails.logger.info "#{batch.jobs.size} jobs completed!"
  end
end

# Create the batch itself. There are three callback options: `on_finish`, `on_success` and `on_failure`
SolidQueue::Batch.enqueue(on_success: BatchCompletionJob) do
  5.times.map { |i| SleepyJob.perform_later(i) }
end

You should see the following in your logs:

[SolidQueue] Claimed 5 jobs
Performing SleepyJob (Job ID: 9a97e394-f1b4-47b5-8db3-6df86faf0913) from SolidQueue(background) enqueued at 2024-02-02T02:02:05.563284000Z with arguments: 1
Feeling 1 seconds sleepy...
Performing SleepyJob (Job ID: 4ae76794-25e1-4378-bbc7-c505d7775395) from SolidQueue(background) enqueued at 2024-02-02T02:02:05.567448000Z with arguments: 2
Feeling 2 seconds sleepy...
Performing SleepyJob (Job ID: fd41b240-08b6-4f7d-b4de-38ee2e6a58b4) from SolidQueue(background) enqueued at 2024-02-02T02:02:05.557246000Z with arguments: 0
Feeling 0 seconds sleepy...
Performed SleepyJob (Job ID: fd41b240-08b6-4f7d-b4de-38ee2e6a58b4) from SolidQueue(background) in 0.1ms
Performing SleepyJob (Job ID: 40498973-9b5a-4f57-acce-03e2b8e2a97c) from SolidQueue(background) enqueued at 2024-02-02T02:02:05.594398000Z with arguments: 4
Feeling 4 seconds sleepy...
Performing SleepyJob (Job ID: c2a123ea-61ba-4d33-99e7-9478a8ca4f5d) from SolidQueue(background) enqueued at 2024-02-02T02:02:05.589439000Z with arguments: 3
Feeling 3 seconds sleepy...
Performed SleepyJob (Job ID: 9a97e394-f1b4-47b5-8db3-6df86faf0913) from SolidQueue(background) in 1005.47ms
Performed SleepyJob (Job ID: 4ae76794-25e1-4378-bbc7-c505d7775395) from SolidQueue(background) in 2006.58ms
Performed SleepyJob (Job ID: c2a123ea-61ba-4d33-99e7-9478a8ca4f5d) from SolidQueue(background) in 3006.1ms
Performed SleepyJob (Job ID: 40498973-9b5a-4f57-acce-03e2b8e2a97c) from SolidQueue(background) in 4008.12ms
[SolidQueue] Claimed 1 jobs
Performing BatchCompletionJob (Job ID: 625ca70c-4e80-4789-988b-3950ed1b23f3) from SolidQueue(background) enqueued at 2024-02-02T02:02:10.183075000Z with arguments: #<GlobalID:0x000000010b5b0390 @uri=#<URI::GID gid://dummy/SolidQueue::JobBatch/13>>
5 jobs completed!
Performed BatchCompletionJob (Job ID: 625ca70c-4e80-4789-988b-3950ed1b23f3) from SolidQueue(background) in 7.97ms

Here is the full interface, demonstrating a few different options:

# All three callback types
# on_finish: runs after all jobs have finished running, including retries. It runs regardless of failed jobs
# on_success: runs after all jobs have finished running, including retries. Only runs if all jobs succeed
# on_failure: runs after all jobs have finished running, including retries. Only runs if one of the jobs fails
SolidQueue::Batch.enqueue(
  # You can hand in a populated instance, to set options like wait times or a custom queue for the callback
  on_finish: BatchCompletionJob.new.set(wait_until: 1.hour.from_now, queue: :batch),
  # Otherwise just supply the job class
  on_success: BatchSuccessJob,
  on_failure: BatchFailureJob
) do
  5.times.map { |i| SleepyJob.perform_later(i) }
end

# Jobs that are part of a batch can enqueue more jobs into the batch
class EnqueueMoreJobsJob < ApplicationJob
  def perform
    batch.enqueue { YetAnotherJob.perform_later }
  end
end

Some have mentioned the GoodJob example for complex batches and asked if this could be implemented in the SolidQueue::Batch approach: https://github.com/bensheldon/good_job?tab=readme-ov-file#complex-batches. GoodJob offers mutable batches, and the SolidQueue::Batch implementation mostly does not. So this is how you would implement the same, more complex example:

class BatchWorkJob < ApplicationJob
  def perform(step)
    puts "BatchWorkJob: #{step}"
    if step == 'e'
      batch.enqueue { BatchWorkJob.perform_later('f') }
      puts "BatchWorkJob: enqueue f"
    end
  end
end

class BatchJob < ApplicationJob
  def perform(batch)
    metadata = batch.metadata
    if metadata[:stage].nil?
      puts "BatchJob: initial stage"
      SolidQueue::Batch.enqueue(on_finish: BatchJob, stage: 1) do
        BatchWorkJob.perform_later('a')
        BatchWorkJob.perform_later('b')
        BatchWorkJob.perform_later('c')
      end
    elsif metadata[:stage] == 1
      puts "BatchJob: stage 1"
      SolidQueue::Batch.enqueue(on_finish: BatchJob, stage: 2) do
        BatchWorkJob.perform_later('d')
        BatchWorkJob.perform_later('e')
      end
    elsif metadata[:stage] == 2
      puts "BatchJob: stage 2"
      # ...
    end
  end
end

SolidQueue::Batch.enqueue(on_finish: BatchJob)

# BatchJob: initial stage
# BatchWorkJob: c
# BatchWorkJob: a
# BatchWorkJob: b
# BatchJob: stage 1
# BatchWorkJob: d
# BatchWorkJob: e
# BatchWorkJob: enqueue f
# BatchWorkJob: f
# BatchJob: stage 2

Here are the things that are open questions and missing implementation details:

• Naming: is JobBatch the right name? General feedback on naming in the feature
• Is it simple enough?
• Do the callbacks make sense? on_success, on_finish, on_failure
• We cannot handle discards right now. SolidQueue handles discard_on by marking the job as finished. That means the batch cannot identify that the job actually failed.
• Hand a generalized interface into the job instead of an actual batch record?
• Keeping things efficient when you have tons of jobs in a batch
• How would/could batches fit into Mission Control - Jobs? Very basic batch support jpcamara/mission_control-jobs#1

[mbajur]

Could that also support adding jobs to already existing batch? Like SleepyJob enqueuing another job that would also be added to the batch.

[jpcamara]

Could that also support adding jobs to already existing batch? Like SleepyJob enqueuing another job that would also be added to the batch.

@mbajur Definitely. As long as you're in a job that's part of the batch, adding another job to the batch would work fine. It'd be pretty simple to extend the existing code to handle that - something like this would solve your use-case I think?

class SleepyJob < ApplicationJob
  queue_as :background

  def perform(seconds_to_sleep)
    Rails.logger.info "Feeling #{seconds_to_sleep} seconds sleepy..."
    sleep seconds_to_sleep

    batch.enqueue { AnotherJob.perform_later }
  end
end

I can update the ActiveJob::JobBatchId to add an extra batch method to the job which returns the current batch based on the job batch_id, and add an instance level SolidQueue::JobBatch#enqueue method which let's you add more jobs to the batch.

This would only work safely inside of the job - if you were outside of the job, it's possible the batch would finish before the job gets created.

[mbajur]

Yes that would absolutely do the trick for me :) Thank you!

[jpcamara]

Hi @rosa 👋🏼 Congrats on getting SolidQueue past incubation and under the Rails umbrella officially!

I'm sure you've got alot on your plate! Are there any questions I can answer in regards to this PR? I can take the interface/functionality further, but I wanted to discuss it a bit before doing that. If there's anything additional you'd like me to tighten up/try out before discussing it, i'm happy to do so.

Also ok to just be on hold and not ready to discuss this further atm. Since it's been a couple months, I figured i'd check in.

[rosa]

Hey @jpcamara, so sorry for the delay and the silence here. I just haven't had the proper time to dedicate to this, and I think this requires and deserves more than a quick look. Thank you so much for putting this together!

My instinct with this kind of feature is that they require someone to use them before they're ready. From just looking at the code, I'm not quite sure what kind of edge cases and race conditions could arise here. This is how most of Solid Queue has been built: we've used it in HEY before making it "official" for everyone, seeing how it behaves under certain loads and what kind of problems we encounter. We caught and improved quite a few things that way.

We don't have a use case for batches right now, so I'm afraid I won't be able to take this feature to this "production-test" point on my side. Do you see yourself using this in a production setting?

[jpcamara]

Hey @jpcamara, so sorry for the delay and the silence here. I just haven't had the proper time to dedicate to this, and I think this requires and deserves more than a quick look. Thank you so much for putting this together!

My instinct with this kind of feature is that they require someone to use them before they're ready. From just looking at the code, I'm not quite sure what kind of edge cases and race conditions could arise here. This is how most of Solid Queue has been built: we've used it in HEY before making it "official" for everyone, seeing how it behaves under certain loads and what kind of problems we encounter. We caught and improved quite a few things that way.

We don't have a use case for batches right now, so I'm afraid I won't be able to take this feature to this "production-test" point on my side. Do you see yourself using this in a production setting?

That makes sense! It was a bit of a chicken and an egg issue for me - I wanted to have batches in SolidQueue before starting to transition some things over, because I have code using Sidekiq Pro batches. But I can start experimenting with it now and report back. I'll continue to work on this PR as well in that case, too.

[dimroc]

Thanks for all the hard work here. I'm a big fan of batch jobs so I've been keeping my eye on this PR for a while. Sidekiq Pro and others support the notion of child batches. Like batch jobs, child batches let you work with a higher level abstraction that conceptually simplifies your background work. While implementing that in this PR would be feature creep, I wanted to raise awareness of it in hopes that we design with its extensibility in mind.

Thanks again @jpcamara

[jpcamara]

Thanks for all the hard work here. I'm a big fan of batch jobs so I've been keeping my eye on this PR for a while. Sidekiq Pro and others support the notion of child batches. Like batch jobs, child batches let you work with a higher level abstraction that conceptually simplifies your background work. While implementing that in this PR would be feature creep, I wanted to raise awareness of it in hopes that we design with its extensibility in mind.

Thanks again @jpcamara

hey @dimroc! I couldn't agree more. I used child batches in Sidekiq recently in a project and it highlighted the need to add them to this PR - it's an important feature. I've been putting alot of work into releasing a blog series on ruby concurrency and it's been eating up my free coding-related time, but i'm prioritizing getting back to this soon. Thanks for the feedback!

[jpcamara]

Thanks for all the hard work here. I'm a big fan of batch jobs so I've been keeping my eye on this PR for a while. Sidekiq Pro and others support the notion of child batches. Like batch jobs, child batches let you work with a higher level abstraction that conceptually simplifies your background work. While implementing that in this PR would be feature creep, I wanted to raise awareness of it in hopes that we design with its extensibility in mind.
Thanks again @jpcamara

hey @dimroc! I couldn't agree more. I used child batches in Sidekiq recently in a project and it highlighted the need to add them to this PR - it's an important feature. I've been putting alot of work into releasing a blog series on ruby concurrency and it's been eating up my free coding-related time, but i'm prioritizing getting back to this soon. Thanks for the feedback!

I've added child batches to this PR @dimroc

[jpcamara]

batch.enqueue { AnotherJob.perform_later }

Added support to this PR for enqueueing within a job using the syntax I suggested: batch.enqueue { AnotherJob.perform_later } @mbajur

[mariochavez]

@jpcamara just an idea here. Could this functionality become its own gem? Like an add-on for solid_queue?
I'm currently using Gush, which is similar to what this functionality does.

[nickpoorman]

One place I think this could be useful could be rolling back changes. Since the move to SQLite doesn't create jobs to a secondary database until after committing records to the main database, there is no atomic guarantee that both records will commit to both databases, leaving us to need manual rollback logic. Additionally, this reminds me that sidekiq had some atomic writing of batch jobs guarantee, either in pro or enterprise.

Same thing might happen if you make a change in your database and call an external API. With SQLite you no longer want to make those changes in your database and make the [long-running] external API call in a transaction. Let's say you have to call stripe twice and want to keep a record of what stage you're at. But something goes wrong with the second stripe call (say the charge is declined) and you need to rollback your database so it's not in an inconsistent state.

In this case you can queue the rollback as part of the batch.

If memory serves, I think the pattern for this sort of thing is called Sagas, or a DAG such as Elixir has with GenStage.

I also found this pattern extremely useful in the past because you can parallelize work more effectively. Say I need to make 1000 remote API calls. Each call should really be in its own job so that it can be retried if it hits the API limits and I need to perform some final job once all 1000 API calls have been made and the batch is complete.

[jpcamara]

@jpcamara just an idea here. Could this functionality become its own gem? Like an add-on for solid_queue? I'm currently using Gush, which is similar to what this functionality does.

@mariochavez it's true, it probably could be a gem! Sidekiq has batches as a pro feature, but there is also an open-source gem that mostly supports the same api https://github.com/breamware/sidekiq-batch.

There are some gotchas with approaching it that way (one, for instance, around jobs being automatically cleaned up and not being able to do anything but warn users against it). But my main motivation is that I personally want it as a first-class feature of SolidQueue. It's a first-class (albeit paid) feature of Sidekiq, and it's a first-class feature of GoodJob. Being built-in means it's more likely to get use/support and alleviates concerns it may be abandoned at some point. I also think it's a great core feature of a job library.

Gush is awesome! It definitely works similarly, though this being backed by a DB in SolidQueue means it has more ACID-type guarantees.

Something I would like to see is an even more sophisticated "workflow" type layer that worked with any activejob system, and that's something I've toyed around wtih over the past year. That kind of system I think goes a step beyond, is more complicated, and is better served as a separate gem. I think batch support being included in the job server is a good fit.

[dimroc]

Thanks for all this work @jpcamara!

I'm curious what the expected behavior is with limit_concurrency. Does it limit concurrency until the batch is complete (ie: only 3 batch jobs can run concurrently even when waiting on their individual jobs), which would surpass even Sidekiq's behavior, or does limit_concurrency only work with individual jobs?

An argument for keeping this in the main gem is to ease integration testing with the other features to increase cohesion and stability. I can see it getting hairy when you stack a few different configurations on top of nested batches, and having to assert proper behavior.

https://github.com/rails/solid_queue?tab=readme-ov-file#concurrency-controls

[abrunner94]

I would love to see batches in Solid Queue! My use case is primarily creating workflows.

[kaka-ruto]

Just wanna thank @jpcamara for the work he's done, is doing here. Would love to use this 🙏

[jpcamara]

Just wanna thank @jpcamara for the work he's done, is doing here. Would love to use this 🙏

Hey @kaka-ruto, I think I saw a message about you being willing to try this out? That would be great! Most of my free time is working on a RubyConf talk I have in a couple weeks, but i'll be shifting back to this right after that and will give you an update.

[rosa]

Ok, I'm finally back at this as well! Thanks a lot for the last push, @jpcamara! 🙏🏻 I'm planning Solid Queue 2.0 with the idea that batches are there.

Regardless, I think due to the use of after_commit in this PR there is always the chance a server crash could happen at a code seam, and maybe require an addition to the maintenance task to also check if any batches happen to have not finished running. Thoughts on this @rosa?

Yes, this seems reasonable to me! Similar to what we do for other cases, like a job failing to unblock the next one for concurrency controls.

I'm planning to add a description field, and an index to the finished_at. The description and finished_at index will improve usage in mission control jobs. I also need to add a Clearable type concern for batches. I added that in my production usage local to that project, to clean up batches. Ideally we'd only have one cleanup task, but that doesn't really gel well with the existing job cleanup that comes in with the template. Thoughts on that @rosa?

Good point. I think it's ok to change that, especially considering we'll change a major version number.

I'm going to do another pass. Thanks a lot!