63 lines
2.2 KiB
Ruby
63 lines
2.2 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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# We can optimize this by using various strategies for approximate counting.
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#
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# For example, we can use the reltuples count as described in https://wiki.postgresql.org/wiki/Slow_Counting.
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#
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# However, since statistics are not always up to date, we also implement a table sampling strategy
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# that performs an exact count but only on a sample of the table. See TablesampleCountStrategy.
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module Gitlab
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module Database
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module Count
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CONNECTION_ERRORS =
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if defined?(PG)
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[
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ActionView::Template::Error,
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ActiveRecord::StatementInvalid,
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PG::Error
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].freeze
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else
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[
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ActionView::Template::Error,
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ActiveRecord::StatementInvalid
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].freeze
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end
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# Takes in an array of models and returns a Hash for the approximate
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# counts for them.
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#
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# Various count strategies can be specified that are executed in
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# sequence until all tables have an approximate count attached
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# or we run out of strategies.
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#
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# Note that not all strategies are available on all supported RDBMS.
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#
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# @param [Array]
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# @return [Hash] of Model -> count mapping
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def self.approximate_counts(models, strategies: [])
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if strategies.empty?
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# ExactCountStrategy is the only strategy working on read-only DBs, as others make
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# use of tuple stats which use the primary DB to estimate tables size in a transaction.
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strategies = if ::Gitlab::Database.read_write?
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[TablesampleCountStrategy, ReltuplesCountStrategy, ExactCountStrategy]
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else
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[ExactCountStrategy]
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end
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end
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strategies.each_with_object({}) do |strategy, counts_by_model|
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models_with_missing_counts = models - counts_by_model.keys
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break counts_by_model if models_with_missing_counts.empty?
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counts = strategy.new(models_with_missing_counts).count
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counts.each do |model, count|
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counts_by_model[model] = 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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end
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end
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