debian-mirror-gitlab/app/models/postgresql/replication_slot.rb

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2018-11-18 11:00:15 +05:30
# frozen_string_literal: true
module Postgresql
class ReplicationSlot < ActiveRecord::Base
self.table_name = 'pg_replication_slots'
# Returns true if the lag observed across all replication slots exceeds a
# given threshold.
#
# max - The maximum replication lag size, in bytes. Based on GitLab.com
# statistics it takes between 1 and 5 seconds to replicate around
# 100 MB of data.
def self.lag_too_great?(max = 100.megabytes)
lag_function = "#{Gitlab::Database.pg_wal_lsn_diff}" \
"(#{Gitlab::Database.pg_current_wal_insert_lsn}(), restart_lsn)::bigint"
# We force the use of a transaction here so the query always goes to the
# primary, even when using the EE DB load balancer.
sizes = transaction { pluck(lag_function) }
too_great = sizes.count { |size| size >= max }
# If too many replicas are falling behind too much, the availability of a
# GitLab instance might suffer. To prevent this from happening we require
# at least 1 replica to have data recent enough.
if sizes.any? && too_great.positive?
(sizes.length - too_great) <= 1
else
false
end
end
end
end