Move strategies in their own files
This improves readability quite a bit.
This commit is contained in:
Andreas Brandl
parent
ff35cb45e9
commit
474fd9138c
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@ -50,161 +50,6 @@ module Gitlab
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end
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end
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end
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# This strategy performs an exact count on the model.
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#
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# This is guaranteed to be accurate, however it also scans the
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# whole table. Hence, there are no guarantees with respect
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# to runtime.
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#
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# Note that for very large tables, this may even timeout.
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class ExactCountStrategy
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attr_reader :models
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def initialize(models)
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@models = models
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end
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def count
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models.each_with_object({}) do |model, data|
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data[model] = model.count
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end
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end
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def self.enabled?
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true
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end
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end
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class PgClass < ActiveRecord::Base
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self.table_name = 'pg_class'
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end
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# This strategy counts based on PostgreSQL's statistics in pg_stat_user_tables.
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#
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# Specifically, it relies on the column reltuples in said table. An additional
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# check is performed to make sure statistics were updated within the last hour.
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#
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# Otherwise, this strategy skips tables with outdated statistics.
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#
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# There are no guarantees with respect to the accuracy of this strategy. Runtime
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# however is guaranteed to be "fast", because it only looks up statistics.
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class ReltuplesCountStrategy
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attr_reader :models
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def initialize(models)
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@models = models
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end
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# Returns a hash of the table names that have recently updated tuples.
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#
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# @returns [Hash] Table name to count mapping (e.g. { 'projects' => 5, 'users' => 100 })
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def count
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size_estimates
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rescue *CONNECTION_ERRORS
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{}
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end
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def self.enabled?
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Gitlab::Database.postgresql?
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end
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private
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def table_names
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models.map(&:table_name)
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end
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def size_estimates(check_statistics: true)
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table_to_model = models.each_with_object({}) { |model, h| h[model.table_name] = model }
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# Querying tuple stats only works on the primary. Due to load balancing, the
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# easiest way to do this is to start a transaction.
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ActiveRecord::Base.transaction do
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get_statistics(table_names, check_statistics: check_statistics).each_with_object({}) do |row, data|
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model = table_to_model[row.table_name]
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data[model] = row.estimate
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end
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end
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end
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# Generates the PostgreSQL query to return the tuples for tables
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# that have been vacuumed or analyzed in the last hour.
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#
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# @param [Array] table names
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# @returns [Hash] Table name to count mapping (e.g. { 'projects' => 5, 'users' => 100 })
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def get_statistics(table_names, check_statistics: true)
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time = "to_timestamp(#{1.hour.ago.to_i})"
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query = PgClass.joins("LEFT JOIN pg_stat_user_tables USING (relname)")
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.where(relname: table_names)
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.select('pg_class.relname AS table_name, reltuples::bigint AS estimate')
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if check_statistics
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query = query.where('last_vacuum > ? OR last_autovacuum > ? OR last_analyze > ? OR last_autoanalyze > ?',
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time, time, time, time)
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end
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query
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end
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end
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# A tablesample count executes in two phases:
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# * Estimate table sizes based on reltuples.
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# * Based on the estimate:
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# * If the table is considered 'small', execute an exact relation count.
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# * Otherwise, count on a sample of the table using TABLESAMPLE.
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#
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# The size of the sample is chosen in a way that we always roughly scan
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# the same amount of rows (see TABLESAMPLE_ROW_TARGET).
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#
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# There are no guarantees with respect to the accuracy of the result or runtime.
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class TablesampleCountStrategy < ReltuplesCountStrategy
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EXACT_COUNT_THRESHOLD = 100_000
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TABLESAMPLE_ROW_TARGET = 100_000
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def count
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estimates = size_estimates(check_statistics: false)
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models.each_with_object({}) do |model, count_by_model|
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count = perform_count(model, estimates[model])
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count_by_model[model] = count if count
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end
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rescue *CONNECTION_ERRORS
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{}
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end
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def self.enabled?
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Gitlab::Database.postgresql? && Feature.enabled?(:tablesample_counts)
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end
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private
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def perform_count(model, estimate)
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# If we estimate 0, we may not have statistics at all. Don't use them.
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return nil unless estimate && estimate > 0
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if estimate < EXACT_COUNT_THRESHOLD
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# The table is considered small, the assumption here is that
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# the exact count will be fast anyways.
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model.count
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else
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# The table is considered large, let's only count on a sample.
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tablesample_count(model, estimate)
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end
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end
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def tablesample_count(model, estimate)
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portion = (TABLESAMPLE_ROW_TARGET.to_f / estimate).round(4)
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inverse = 1 / portion
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query = <<~SQL
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SELECT (COUNT(*)*#{inverse})::integer AS count
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FROM #{model.table_name} TABLESAMPLE SYSTEM (#{portion * 100})
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SQL
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rows = ActiveRecord::Base.connection.select_all(query)
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Integer(rows.first['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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@ -0,0 +1,31 @@
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# frozen_string_literal: true
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module Gitlab
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module Database
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module Count
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# This strategy performs an exact count on the model.
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#
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# This is guaranteed to be accurate, however it also scans the
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# whole table. Hence, there are no guarantees with respect
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# to runtime.
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#
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# Note that for very large tables, this may even timeout.
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class ExactCountStrategy
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attr_reader :models
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def initialize(models)
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@models = models
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end
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def count
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models.each_with_object({}) do |model, data|
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data[model] = model.count
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end
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end
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def self.enabled?
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true
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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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@ -0,0 +1,79 @@
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# frozen_string_literal: true
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module Gitlab
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module Database
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module Count
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class PgClass < ActiveRecord::Base
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self.table_name = 'pg_class'
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end
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# This strategy counts based on PostgreSQL's statistics in pg_stat_user_tables.
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#
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# Specifically, it relies on the column reltuples in said table. An additional
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# check is performed to make sure statistics were updated within the last hour.
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#
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# Otherwise, this strategy skips tables with outdated statistics.
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#
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# There are no guarantees with respect to the accuracy of this strategy. Runtime
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# however is guaranteed to be "fast", because it only looks up statistics.
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class ReltuplesCountStrategy
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attr_reader :models
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def initialize(models)
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@models = models
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end
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# Returns a hash of the table names that have recently updated tuples.
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#
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# @returns [Hash] Table name to count mapping (e.g. { 'projects' => 5, 'users' => 100 })
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def count
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size_estimates
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rescue *CONNECTION_ERRORS
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{}
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end
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def self.enabled?
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Gitlab::Database.postgresql?
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end
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private
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def table_names
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models.map(&:table_name)
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end
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def size_estimates(check_statistics: true)
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table_to_model = models.each_with_object({}) { |model, h| h[model.table_name] = model }
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# Querying tuple stats only works on the primary. Due to load balancing, the
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# easiest way to do this is to start a transaction.
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ActiveRecord::Base.transaction do
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get_statistics(table_names, check_statistics: check_statistics).each_with_object({}) do |row, data|
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model = table_to_model[row.table_name]
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data[model] = row.estimate
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end
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end
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end
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# Generates the PostgreSQL query to return the tuples for tables
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# that have been vacuumed or analyzed in the last hour.
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#
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# @param [Array] table names
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# @returns [Hash] Table name to count mapping (e.g. { 'projects' => 5, 'users' => 100 })
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def get_statistics(table_names, check_statistics: true)
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time = 1.hour.ago
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query = PgClass.joins("LEFT JOIN pg_stat_user_tables USING (relname)")
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.where(relname: table_names)
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.select('pg_class.relname AS table_name, reltuples::bigint AS estimate')
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if check_statistics
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query = query.where('last_vacuum > ? OR last_autovacuum > ? OR last_analyze > ? OR last_autoanalyze > ?',
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time, time, time, time)
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end
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query
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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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@ -0,0 +1,66 @@
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# frozen_string_literal: true
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module Gitlab
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module Database
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module Count
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# A tablesample count executes in two phases:
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# * Estimate table sizes based on reltuples.
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# * Based on the estimate:
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# * If the table is considered 'small', execute an exact relation count.
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# * Otherwise, count on a sample of the table using TABLESAMPLE.
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#
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# The size of the sample is chosen in a way that we always roughly scan
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# the same amount of rows (see TABLESAMPLE_ROW_TARGET).
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#
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# There are no guarantees with respect to the accuracy of the result or runtime.
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class TablesampleCountStrategy < ReltuplesCountStrategy
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EXACT_COUNT_THRESHOLD = 100_000
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TABLESAMPLE_ROW_TARGET = 100_000
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def count
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estimates = size_estimates(check_statistics: false)
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models.each_with_object({}) do |model, count_by_model|
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count = perform_count(model, estimates[model])
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count_by_model[model] = count if count
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end
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rescue *CONNECTION_ERRORS
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{}
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end
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def self.enabled?
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Gitlab::Database.postgresql? && Feature.enabled?(:tablesample_counts)
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end
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private
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def perform_count(model, estimate)
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# If we estimate 0, we may not have statistics at all. Don't use them.
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return nil unless estimate && estimate > 0
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if estimate < EXACT_COUNT_THRESHOLD
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# The table is considered small, the assumption here is that
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# the exact count will be fast anyways.
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model.count
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else
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# The table is considered large, let's only count on a sample.
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tablesample_count(model, estimate)
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end
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end
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def tablesample_count(model, estimate)
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portion = (TABLESAMPLE_ROW_TARGET.to_f / estimate).round(4)
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inverse = 1 / portion
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query = <<~SQL
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SELECT (COUNT(*)*#{inverse})::integer AS count
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FROM #{model.table_name} TABLESAMPLE SYSTEM (#{portion * 100})
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SQL
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rows = ActiveRecord::Base.connection.select_all(query)
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Integer(rows.first['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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@ -0,0 +1,34 @@
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require 'spec_helper'
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describe Gitlab::Database::Count::ExactCountStrategy do
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before do
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create_list(:project, 3)
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create(:identity)
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end
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let(:models) { [Project, Identity] }
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subject { described_class.new(models).count }
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describe '#count' do
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it 'counts all models' do
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expect(models).to all(receive(:count).and_call_original)
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expect(subject).to eq({ Project => 3, Identity => 1 })
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end
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end
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describe '.enabled?' do
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it 'is enabled for PostgreSQL' do
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allow(Gitlab::Database).to receive(:postgresql?).and_return(true)
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expect(described_class.enabled?).to be_truthy
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end
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it 'is enabled for MySQL' do
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allow(Gitlab::Database).to receive(:postgresql?).and_return(false)
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expect(described_class.enabled?).to be_truthy
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end
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end
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end
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@ -0,0 +1,48 @@
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require 'spec_helper'
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describe Gitlab::Database::Count::ReltuplesCountStrategy do
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before do
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create_list(:project, 3)
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create(:identity)
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end
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let(:models) { [Project, Identity] }
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subject { described_class.new(models).count }
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describe '#count', :postgresql do
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context 'when reltuples is up to date' do
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before do
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ActiveRecord::Base.connection.execute('ANALYZE projects')
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ActiveRecord::Base.connection.execute('ANALYZE identities')
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end
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it 'uses statistics to do the count' do
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models.each { |model| expect(model).not_to receive(:count) }
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expect(subject).to eq({ Project => 3, Identity => 1 })
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end
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end
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context 'insufficient permissions' do
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it 'returns an empty hash' do
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allow(ActiveRecord::Base).to receive(:transaction).and_raise(PG::InsufficientPrivilege)
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expect(subject).to eq({})
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end
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end
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end
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describe '.enabled?' do
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it 'is enabled for PostgreSQL' do
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allow(Gitlab::Database).to receive(:postgresql?).and_return(true)
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expect(described_class.enabled?).to be_truthy
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end
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it 'is disabled for MySQL' do
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allow(Gitlab::Database).to receive(:postgresql?).and_return(false)
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expect(described_class.enabled?).to be_falsey
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end
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end
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end
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@ -0,0 +1,65 @@
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require 'spec_helper'
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describe Gitlab::Database::Count::TablesampleCountStrategy do
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before do
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create_list(:project, 3)
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create(:identity)
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end
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let(:models) { [Project, Identity] }
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let(:strategy) { described_class.new(models) }
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subject { strategy.count }
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describe '#count', :postgresql do
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let(:estimates) { { Project => threshold + 1, Identity => threshold - 1 } }
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let(:threshold) { Gitlab::Database::Count::TablesampleCountStrategy::EXACT_COUNT_THRESHOLD }
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before do
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allow(strategy).to receive(:size_estimates).with(check_statistics: false).and_return(estimates)
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end
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context 'for tables with an estimated small size' do
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it 'performs an exact count' do
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expect(Identity).to receive(:count).and_call_original
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expect(subject).to include({ Identity => 1 })
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end
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end
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context 'for tables with an estimated large size' do
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it 'performs a tablesample count' do
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expect(Project).not_to receive(:count)
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result = subject
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expect(result[Project]).to eq(3)
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end
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end
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context 'insufficient permissions' do
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it 'returns an empty hash' do
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allow(strategy).to receive(:size_estimates).and_raise(PG::InsufficientPrivilege)
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expect(subject).to eq({})
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end
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end
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end
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describe '.enabled?' do
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before do
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stub_feature_flags(tablesample_counts: true)
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end
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it 'is enabled for PostgreSQL' do
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allow(Gitlab::Database).to receive(:postgresql?).and_return(true)
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expect(described_class.enabled?).to be_truthy
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end
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it 'is disabled for MySQL' do
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allow(Gitlab::Database).to receive(:postgresql?).and_return(false)
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expect(described_class.enabled?).to be_falsey
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end
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end
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end
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@ -56,128 +56,4 @@ describe Gitlab::Database::Count do
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end
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end
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end
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describe Gitlab::Database::Count::ExactCountStrategy do
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subject { described_class.new(models).count }
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describe '#count' do
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it 'counts all models' do
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expect(models).to all(receive(:count).and_call_original)
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expect(subject).to eq({ Project => 3, Identity => 1 })
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end
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end
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describe '.enabled?' do
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it 'is enabled for PostgreSQL' do
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allow(Gitlab::Database).to receive(:postgresql?).and_return(true)
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expect(described_class.enabled?).to be_truthy
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end
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it 'is enabled for MySQL' do
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allow(Gitlab::Database).to receive(:postgresql?).and_return(false)
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expect(described_class.enabled?).to be_truthy
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end
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end
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end
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describe Gitlab::Database::Count::ReltuplesCountStrategy do
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subject { described_class.new(models).count }
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describe '#count', :postgresql do
|
||||
context 'when reltuples is up to date' do
|
||||
before do
|
||||
ActiveRecord::Base.connection.execute('ANALYZE projects')
|
||||
ActiveRecord::Base.connection.execute('ANALYZE identities')
|
||||
end
|
||||
|
||||
it 'uses statistics to do the count' do
|
||||
models.each { |model| expect(model).not_to receive(:count) }
|
||||
|
||||
expect(subject).to eq({ Project => 3, Identity => 1 })
|
||||
end
|
||||
end
|
||||
|
||||
context 'insufficient permissions' do
|
||||
it 'returns an empty hash' do
|
||||
allow(ActiveRecord::Base).to receive(:transaction).and_raise(PG::InsufficientPrivilege)
|
||||
|
||||
expect(subject).to eq({})
|
||||
end
|
||||
end
|
||||
end
|
||||
|
||||
describe '.enabled?' do
|
||||
it 'is enabled for PostgreSQL' do
|
||||
allow(Gitlab::Database).to receive(:postgresql?).and_return(true)
|
||||
|
||||
expect(described_class.enabled?).to be_truthy
|
||||
end
|
||||
|
||||
it 'is disabled for MySQL' do
|
||||
allow(Gitlab::Database).to receive(:postgresql?).and_return(false)
|
||||
|
||||
expect(described_class.enabled?).to be_falsey
|
||||
end
|
||||
end
|
||||
end
|
||||
|
||||
describe Gitlab::Database::Count::TablesampleCountStrategy do
|
||||
subject { strategy.count }
|
||||
let(:strategy) { described_class.new(models) }
|
||||
|
||||
describe '#count', :postgresql do
|
||||
let(:estimates) { { Project => threshold + 1, Identity => threshold - 1 } }
|
||||
let(:threshold) { Gitlab::Database::Count::TablesampleCountStrategy::EXACT_COUNT_THRESHOLD }
|
||||
|
||||
before do
|
||||
allow(strategy).to receive(:size_estimates).with(check_statistics: false).and_return(estimates)
|
||||
end
|
||||
|
||||
context 'for tables with an estimated small size' do
|
||||
it 'performs an exact count' do
|
||||
expect(Identity).to receive(:count).and_call_original
|
||||
|
||||
expect(subject).to include({ Identity => 1 })
|
||||
end
|
||||
end
|
||||
|
||||
context 'for tables with an estimated large size' do
|
||||
it 'performs a tablesample count' do
|
||||
expect(Project).not_to receive(:count)
|
||||
|
||||
result = subject
|
||||
expect(result[Project]).to eq(3)
|
||||
end
|
||||
end
|
||||
|
||||
context 'insufficient permissions' do
|
||||
it 'returns an empty hash' do
|
||||
allow(strategy).to receive(:size_estimates).and_raise(PG::InsufficientPrivilege)
|
||||
|
||||
expect(subject).to eq({})
|
||||
end
|
||||
end
|
||||
end
|
||||
|
||||
describe '.enabled?' do
|
||||
before do
|
||||
stub_feature_flags(tablesample_counts: true)
|
||||
end
|
||||
|
||||
it 'is enabled for PostgreSQL' do
|
||||
allow(Gitlab::Database).to receive(:postgresql?).and_return(true)
|
||||
|
||||
expect(described_class.enabled?).to be_truthy
|
||||
end
|
||||
|
||||
it 'is disabled for MySQL' do
|
||||
allow(Gitlab::Database).to receive(:postgresql?).and_return(false)
|
||||
|
||||
expect(described_class.enabled?).to be_falsey
|
||||
end
|
||||
end
|
||||
end
|
||||
end
|
||||
|
|
|
|||
Loading…
Reference in New Issue