90 lines
3.1 KiB
Ruby
90 lines
3.1 KiB
Ruby
# frozen_string_literal: true
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# For large tables, PostgreSQL can take a long time to count rows due to MVCC.
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# Implements a distinct and ordinary batch counter
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# Needs indexes on the column below to calculate max, min and range queries
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# For larger tables just set use higher batch_size with index optimization
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# See https://gitlab.com/gitlab-org/gitlab/-/merge_requests/22705
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# Examples:
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# extend ::Gitlab::Database::BatchCount
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# batch_count(User.active)
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# batch_count(::Clusters::Cluster.aws_installed.enabled, :cluster_id)
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# batch_distinct_count(::Project, :creator_id)
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module Gitlab
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module Database
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module BatchCount
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def batch_count(relation, column = nil, batch_size: nil)
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BatchCounter.new(relation, column: column).count(batch_size: batch_size)
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end
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def batch_distinct_count(relation, column = nil, batch_size: nil)
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BatchCounter.new(relation, column: column).count(mode: :distinct, batch_size: batch_size)
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end
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class << self
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include BatchCount
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end
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end
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class BatchCounter
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FALLBACK = -1
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MIN_REQUIRED_BATCH_SIZE = 2_000
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MAX_ALLOWED_LOOPS = 10_000
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SLEEP_TIME_IN_SECONDS = 0.01 # 10 msec sleep
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# Each query should take <<500ms https://gitlab.com/gitlab-org/gitlab/-/merge_requests/22705
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DEFAULT_DISTINCT_BATCH_SIZE = 100_000
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DEFAULT_BATCH_SIZE = 10_000
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def initialize(relation, column: nil)
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@relation = relation
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@column = column || relation.primary_key
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end
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def unwanted_configuration?(finish, batch_size, start)
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batch_size <= MIN_REQUIRED_BATCH_SIZE ||
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(finish - start) / batch_size >= MAX_ALLOWED_LOOPS ||
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start > finish
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end
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def count(batch_size: nil, mode: :itself)
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raise 'BatchCount can not be run inside a transaction' if ActiveRecord::Base.connection.transaction_open?
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raise "The mode #{mode.inspect} is not supported" unless [:itself, :distinct].include?(mode)
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# non-distinct have better performance
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batch_size ||= mode == :distinct ? DEFAULT_BATCH_SIZE : DEFAULT_DISTINCT_BATCH_SIZE
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start = @relation.minimum(@column) || 0
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finish = @relation.maximum(@column) || 0
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raise "Batch counting expects positive values only for #{@column}" if start < 0 || finish < 0
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return FALLBACK if unwanted_configuration?(finish, batch_size, start)
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counter = 0
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batch_start = start
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while batch_start <= finish
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begin
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counter += batch_fetch(batch_start, batch_start + batch_size, mode)
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batch_start += batch_size
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rescue ActiveRecord::QueryCanceled
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# retry with a safe batch size & warmer cache
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if batch_size >= 2 * MIN_REQUIRED_BATCH_SIZE
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batch_size /= 2
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else
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return FALLBACK
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end
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end
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sleep(SLEEP_TIME_IN_SECONDS)
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end
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counter
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end
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def batch_fetch(start, finish, mode)
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# rubocop:disable GitlabSecurity/PublicSend
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@relation.select(@column).public_send(mode).where(@column => start..(finish - 1)).count
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end
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end
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end
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end
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