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# frozen_string_literal: true
module Gitlab
module Database
module Count
class PgClass < ActiveRecord::Base
self.table_name = 'pg_class'
end
# This strategy counts based on PostgreSQL's statistics in pg_stat_user_tables.
#
# Specifically, it relies on the column reltuples in said table. An additional
# check is performed to make sure statistics were updated within the last hour.
#
# Otherwise, this strategy skips tables with outdated statistics.
#
# There are no guarantees with respect to the accuracy of this strategy. Runtime
# however is guaranteed to be "fast", because it only looks up statistics.
class ReltuplesCountStrategy
attr_reader :models
def initialize(models)
@models = models
end
# Returns a hash of the table names that have recently updated tuples.
#
# @returns [Hash] Table name to count mapping (e.g. { 'projects' => 5, 'users' => 100 })
def count
size_estimates
rescue *CONNECTION_ERRORS
{}
end
def self.enabled?
Gitlab::Database.postgresql?
end
private
# Models using single-type inheritance (STI) don't work with
# reltuple count estimates. We just have to ignore them and
# use another strategy to compute them.
def non_sti_models
models.reject { |model| sti_model?(model) }
end
def non_sti_table_names
non_sti_models.map(&:table_name)
end
def sti_model?(model)
model.column_names.include?(model.inheritance_column) &&
model.base_class != model
end
def table_names
models.map(&:table_name)
end
def size_estimates(check_statistics: true)
table_to_model = models.each_with_object({}) { |model, h| h[model.table_name] = model }
# Querying tuple stats only works on the primary. Due to load balancing, the
# easiest way to do this is to start a transaction.
ActiveRecord::Base.transaction do
get_statistics(non_sti_table_names, check_statistics: check_statistics).each_with_object({}) do |row, data|
model = table_to_model[row.table_name]
data[model] = row.estimate
end
end
end
# Generates the PostgreSQL query to return the tuples for tables
# that have been vacuumed or analyzed in the last hour.
#
# @param [Array] table names
# @returns [Hash] Table name to count mapping (e.g. { 'projects' => 5, 'users' => 100 })
def get_statistics(table_names, check_statistics: true)
time = 1.hour.ago
query = PgClass.joins("LEFT JOIN pg_stat_user_tables USING (relname)")
.where(relname: table_names)
.select('pg_class.relname AS table_name, reltuples::bigint AS estimate')
if check_statistics
query = query.where('last_vacuum > ? OR last_autovacuum > ? OR last_analyze > ? OR last_autoanalyze > ?',
time, time, time, time)
end
query
end
end
end
end
end
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