Class: SwitchmanInstJobs::JobsMigrator

Inherits:
Object
  • Object
show all
Defined in:
lib/switchman_inst_jobs/jobs_migrator.rb

Class Method Summary collapse

Class Method Details

.acquire_advisory_lock(type, name) ⇒ Object 



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# File 'lib/switchman_inst_jobs/jobs_migrator.rb', line 100

def acquire_advisory_lock(type, name)
  @quoted_function_name ||= ::Delayed::Job.connection.quote_table_name("half_md5_as_bigint")

  value = (type == :singleton) ? "singleton:#{name}" : name
  ::Delayed::Job.connection.execute(
    ::Delayed::Job.sanitize_sql_for_conditions(
      ["SELECT pg_advisory_xact_lock(#{@quoted_function_name}(?))", value]
    )
  )
end

.add_before_move_callback(proc) ⇒ Object 



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# File 'lib/switchman_inst_jobs/jobs_migrator.rb', line 9

def add_before_move_callback(proc)
  @before_move_callbacks ||= []
  @before_move_callbacks << proc
end

.add_validation_callback(proc) ⇒ Object 



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# File 'lib/switchman_inst_jobs/jobs_migrator.rb', line 14

def add_validation_callback(proc)
  @validation_callbacks ||= []
  @validation_callbacks << proc
end

.blocked_by_migrator?(job_scope) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/switchman_inst_jobs/jobs_migrator.rb', line 281

def blocked_by_migrator?(job_scope)
  job_scope.exists?(source: "JobsMigrator::StrandBlocker") ||
    blocked_shards.exists?(id: job_scope.distinct.pluck(:shard_id))
end

.blocked_job_count ⇒ Object 



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# File 'lib/switchman_inst_jobs/jobs_migrator.rb', line 342

def blocked_job_count
  ::Delayed::Job.from(blocked_strands.select("count(id) AS ssize")).sum("ssize").to_i +
    ::Delayed::Job.from(blocked_singletons.select("count(id) AS ssize")).sum("ssize").to_i +
    ::Delayed::Job.where(strand: nil, singleton: nil, next_in_strand: false).count
end

.blocked_shards ⇒ Object 



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# File 'lib/switchman_inst_jobs/jobs_migrator.rb', line 277

def blocked_shards
  ::Switchman::Shard.where(block_stranded: true).or(::Switchman::Shard.where(jobs_held: true))
end

.blocked_singletons ⇒ Object 



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# File 'lib/switchman_inst_jobs/jobs_migrator.rb', line 315

def blocked_singletons
  ::Delayed::Job
    .where(strand: nil)
    .where.not(singleton: nil)
    .group(:singleton)
    .having("NOT BOOL_OR(next_in_strand)")
end

.blocked_strands ⇒ Object 



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# File 'lib/switchman_inst_jobs/jobs_migrator.rb', line 286

def blocked_strands
  ::Delayed::Job
    .where.not(strand: nil)
    .group(:strand)
    .having("NOT BOOL_OR(next_in_strand)")
end

.clear_callbacks! ⇒ Object 



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# File 'lib/switchman_inst_jobs/jobs_migrator.rb', line 19

def clear_callbacks!
  @before_move_callbacks = []
  @validation_callbacks = []
end

.clear_shard_cache(debug_message = nil, default:) ⇒ Object 



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# File 'lib/switchman_inst_jobs/jobs_migrator.rb', line 89

def clear_shard_cache(debug_message = nil, default:)
  ::Switchman.cache.delete_matched("shard/*")
  ::Switchman.cache.delete("default_shard") if default
  Rails.logger.debug { "Waiting for caches to clear #{debug_message}" }
  # Wait a little over the 60 second in-process shard cache clearing
  # threshold to ensure that all new stranded jobs are now being
  # enqueued with next_in_strand: false
  # @skip_cache_wait is for spec usage only
  sleep(65) unless @skip_cache_wait
end

.ensure_unblock_stranded_for(shards) ⇒ Object

if :migrate_strands ran on any shards that fell into scenario 1, then block_stranded never got flipped, so do that now.



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# File 'lib/switchman_inst_jobs/jobs_migrator.rb', line 76

def ensure_unblock_stranded_for(shards)
  shards = ::Switchman::Shard.where(id: shards, block_stranded: true).to_a
  return unless shards.any?

  ::Switchman::Shard.where(id: shards).update_all(block_stranded: false)
  clear_shard_cache(default: shards.any?(&:default?))

  # shards is an array of shard objects that is now stale cause block_stranded has been updated.
  shards.map(&:delayed_jobs_shard).uniq.each do |dj_shard|
    unblock_strands(dj_shard)
  end
end

.migrate_everything(batch_size: 1_000) ⇒ Object 



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# File 'lib/switchman_inst_jobs/jobs_migrator.rb', line 262

def migrate_everything(batch_size: 1_000)
  source_shard = ::Switchman::Shard.current(::Delayed::Backend::ActiveRecord::AbstractJob)
  scope = ::Delayed::Job.shard(source_shard).where(strand: nil)

  shard_map = build_shard_map(scope, source_shard)
  shard_map.each do |(target_shard, source_shard_ids)|
    batch_move_jobs(
      target_shard: target_shard,
      source_shard: source_shard,
      scope: scope.where(shard_id: source_shard_ids).where(locked_by: nil),
      batch_size: batch_size
    )
  end
end

.migrate_shards(shard_map) ⇒ Object 



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# File 'lib/switchman_inst_jobs/jobs_migrator.rb', line 38

def migrate_shards(shard_map)
  source_shards = Set[]
  target_shards = Hash.new([])
  shard_map.each do |(shard, target_shard)|
    shard = ::Switchman::Shard.find(shard) unless shard.is_a?(::Switchman::Shard)
    source_shards << shard.delayed_jobs_shard.id
    target_shard = target_shard.try(:id) || target_shard
    target_shards[target_shard] += [shard.id]

    @validation_callbacks&.each do |proc|
      proc.call(shard: shard, target_shard: ::Switchman::Shard.find(target_shard))
    end
  end

  # Do the updates in batches and then just clear redis instead of clearing them one at a time
  target_shards.each do |target_shard, shards|
    updates = { delayed_jobs_shard_id: target_shard, block_stranded: true }
    updates[:updated_at] = Time.zone.now if ::Switchman::Shard.column_names.include?("updated_at")
    ::Switchman::Shard.where(id: shards).update_all(updates)
  end
  clear_shard_cache(default: ::Switchman::Shard.exists?(id: target_shards.values.flatten, default: true))

  ::Switchman::Shard.clear_cache
  # rubocop:disable Style/CombinableLoops
  # We first migrate strands so that we can stop blocking strands before we migrate unstranded jobs
  source_shards.each do |s|
    ::Switchman::Shard.lookup(s).activate(::Delayed::Backend::ActiveRecord::AbstractJob) { migrate_strands }
  end

  source_shards.each do |s|
    ::Switchman::Shard.lookup(s).activate(::Delayed::Backend::ActiveRecord::AbstractJob) { migrate_everything }
  end
  ensure_unblock_stranded_for(shard_map.map(&:first))
  # rubocop:enable Style/CombinableLoops
end

.migrate_strands(batch_size: 1_000) ⇒ Object 



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# File 'lib/switchman_inst_jobs/jobs_migrator.rb', line 120

def migrate_strands(batch_size: 1_000)
  source_shard = ::Switchman::Shard.current(::Delayed::Backend::ActiveRecord::AbstractJob)

  # there are 4 scenarios to deal with here
  # 1) no running job, no jobs moved: do nothing
  # 2) running job, no jobs moved; create blocker with next_in_strand=false
  #    to prevent new jobs from immediately executing
  # 3) running job, jobs moved; set next_in_strand=false on the first of
  #    those (= do nothing since it should already be false)
  # 4) no running job, jobs moved: set next_in_strand=true on the first of
  #    those (= do nothing since it should already be true)
  handler = lambda { |scope, column, blocker_job_kwargs = {}, advisory_lock_cb = nil|
    shard_map = build_shard_map(scope, source_shard)
    shard_map.each do |(target_shard, source_shard_ids)|
      shard_scope = scope.where(shard_id: source_shard_ids)

      # 1) is taken care of because it should not show up here in strands
      values = shard_scope.distinct.order(column).pluck(column)

      target_shard.activate(::Delayed::Backend::ActiveRecord::AbstractJob) do
        values.each do |value|
          transaction_on([source_shard, target_shard]) do
            source_shard.activate(::Delayed::Backend::ActiveRecord::AbstractJob) do
              advisory_lock_cb&.call(value)
            end

            value_scope = shard_scope.where(**{ column => value })
            # we want to copy all the jobs except the one that is still running.
            jobs_scope = value_scope.where(locked_by: nil)

            # 2) and part of 3) are taken care of here by creating a blocker
            # job with next_in_strand = false. as soon as the current
            # running job is finished it should set next_in_strand
            # We lock it to ensure that the jobs worker can't delete it until we are done moving the strand
            # Since we only unlock it on the new jobs queue *after* deleting from the original
            # the lock ensures the blocker always gets unlocked
            first = value_scope.where.not(locked_by: nil).next_in_strand_order.lock.first
            if first
              create_blocker_job(
                queue: first.queue,
                shard_id: first.shard_id,
                **{ column => value },
                **blocker_job_kwargs
              )

              # the rest of 3) is taken care of here
              # make sure that all the jobs moved over are NOT next in strand
              ::Delayed::Job.where(next_in_strand: true, locked_by: nil, **{ column => value })
                            .update_all(next_in_strand: false)
            end

            # 4) is taken care of here, by leaving next_in_strand alone and
            # it should execute on the new shard
            batch_move_jobs(
              target_shard: target_shard,
              source_shard: source_shard,
              scope: jobs_scope,
              batch_size: batch_size
            ) do |job, new_job|
              # This ensures jobs enqueued on the old jobs shard run before jobs on the new jobs queue
              new_job.strand_order_override = job.strand_order_override - 1
            end
          end
        end
      end
    end
  }

  strand_scope = ::Delayed::Job.shard(source_shard).where.not(strand: nil)
  singleton_scope = ::Delayed::Job.shard(source_shard).where("strand IS NULL AND singleton IS NOT NULL")
  all_scope = ::Delayed::Job.shard(source_shard).where("strand IS NOT NULL OR singleton IS NOT NULL")

  singleton_blocker_additional_kwargs = {
    locked_at: DateTime.now,
    locked_by: ::Delayed::Backend::Base::ON_HOLD_BLOCKER
  }

  strand_advisory_lock_fn = lambda do |value|
    acquire_advisory_lock(:strand, value)
  end

  singleton_advisory_lock_fn = lambda do |value|
    acquire_advisory_lock(:singleton, value)
  end

  handler.call(strand_scope, :strand, {}, strand_advisory_lock_fn)
  handler.call(singleton_scope, :singleton, singleton_blocker_additional_kwargs, singleton_advisory_lock_fn)

  shard_map = build_shard_map(all_scope, source_shard)
  shard_map.each do |(target_shard, source_shard_ids)|
    target_shard.activate(::Delayed::Backend::ActiveRecord::AbstractJob) do
      updated = ::Switchman::Shard.where(id: source_shard_ids, block_stranded: true)
                                  .update_all(block_stranded: false)
      # If this is being manually re-run for some reason to clean something up, don't wait for nothing to happen
      unless updated.zero?
        clear_shard_cache("(#{source_shard.id} -> #{target_shard.id})",
                          default: ::Switchman::Shard.exists?(id: source_shard_ids,
                                                              default: true))
      end

      ::Switchman::Shard.clear_cache
      # At this time, let's unblock all the strands on the target shard that aren't being held by a blocker
      # but actually could have run and we just didn't know it because we didn't know if they had jobs
      # on the source shard
      unblock_strands(target_shard)
    end
  end
end

.run ⇒ Object

This method expects that all relevant shards already have block_stranded: true but otherwise jobs can be running normally



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# File 'lib/switchman_inst_jobs/jobs_migrator.rb', line 113

def run
  # Ensure this is never run with a dirty in-memory shard cache
  ::Switchman::Shard.clear_cache
  migrate_strands
  migrate_everything
end

.transaction_on(shards, &block) ⇒ Object 



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# File 'lib/switchman_inst_jobs/jobs_migrator.rb', line 24

def transaction_on(shards, &block)
  return yield if shards.empty?

  shard = shards.pop
  current_shard = ::Switchman::Shard.current(::Delayed::Backend::ActiveRecord::AbstractJob)
  shard.activate(::Delayed::Backend::ActiveRecord::AbstractJob) do
    ::Delayed::Job.transaction do
      current_shard.activate(::Delayed::Backend::ActiveRecord::AbstractJob) do
        transaction_on(shards, &block)
      end
    end
  end
end

.unblock_singleton!(singleton) ⇒ Object

Raises:



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# File 'lib/switchman_inst_jobs/jobs_migrator.rb', line 323

def unblock_singleton!(singleton)
  job_scope = ::Delayed::Job.where(strand: nil, singleton: singleton)
  raise JobsBlockedError if blocked_by_migrator?(job_scope)

  ::Delayed::Job.transaction do
    acquire_advisory_lock(:singleton, singleton)

    id, next_in_strand = job_scope
                         .group(:singleton)
                         .pick("MIN(id), BOOL_OR(next_in_strand)")

    if next_in_strand
      0
    elsif id
      ::Delayed::Job.where(id: id).update_all(next_in_strand: true)
    end
  end
end

.unblock_strand!(strand, new_parallelism: nil) ⇒ Object

Raises:



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# File 'lib/switchman_inst_jobs/jobs_migrator.rb', line 293

def unblock_strand!(strand, new_parallelism: nil)
  job_scope = ::Delayed::Job.where(strand: strand)
  raise JobsBlockedError if blocked_by_migrator?(job_scope)

  ::Delayed::Job.transaction do
    acquire_advisory_lock(:strand, strand)

    new_parallelism ||= job_scope.pick("MAX(max_concurrent)")
    if new_parallelism
      needed_jobs = new_parallelism - job_scope.where(next_in_strand: true).count
      if needed_jobs.positive?
        job_scope.where(next_in_strand: false,
                        locked_by: nil,
                        singleton: nil).order(:strand_order_override, :id)
                 .limit(needed_jobs).update_all(next_in_strand: true)
      else
        0
      end
    end
  end
end

.unblock_strands(target_shard, batch_size: 10_000) ⇒ Object 



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# File 'lib/switchman_inst_jobs/jobs_migrator.rb', line 229

def unblock_strands(target_shard, batch_size: 10_000)
  blocked_shard_ids = blocked_shards.pluck(:id)
  query = lambda { |column, scope|
    ::Delayed::Job
      .where(id: ::Delayed::Job.select("DISTINCT ON (#{column}) id")
        .where(scope)
        .where.not(shard_id: blocked_shard_ids)
        .where(
          ::Delayed::Job.select(1).from("#{::Delayed::Job.quoted_table_name} dj2")
          .where("dj2.next_in_strand = true OR dj2.source = 'JobsMigrator::StrandBlocker'")
          .where("dj2.#{column} = delayed_jobs.#{column}").arel.exists.not
        )
        .order(column, :strand_order_override, :id)).limit(batch_size)
  }

  target_shard.activate(::Delayed::Backend::ActiveRecord::AbstractJob) do
    # We only want to unlock stranded jobs where they don't belong to a blocked shard (if they *do* belong)
    # to a blocked shard, they must be part of a concurrent jobs migration from a different source shard to
    # this target shard, so we shouldn't unlock them yet.  We only ever unlock one job here to keep the
    # logic cleaner; if the job is n-stranded, after the first one runs, the trigger will unlock larger
    # batches

    loop do
      break if query.call(:strand, "strand IS NOT NULL").update_all(next_in_strand: true).zero?
    end

    loop do
      break if query.call(:singleton,
                          "strand IS NULL AND singleton IS NOT NULL").update_all(next_in_strand: true).zero?
    end
  end
end