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# frozen_string_literal: true
module Gitlab
module Database
module LoadBalancing
# Module used for handling sticking connections to a primary, if
# necessary.
class Sticking
# The number of seconds after which a session should stop reading from
# the primary.
EXPIRATION = 30
def initialize(load_balancer)
@load_balancer = load_balancer
end
# Returns true if any caught up replica is found. This does not mean all replicas are caught up but the found
# caught up replica will be stored in the SafeRequestStore available as LoadBalancer#host for future queries.
# With use_primary_on_empty_location: true we will assume you need the primary if we can't find a matching
# location for the namespace, id pair. You should only use use_primary_on_empty_location in rare cases because
# we unstick once we find all replicas are caught up one time so it can be wasteful on the primary.
def find_caught_up_replica(namespace, id, use_primary_on_failure: true, use_primary_on_empty_location: false)
location = last_write_location_for(namespace, id)
result = if location
up_to_date_result = @load_balancer.select_up_to_date_host(location)
unstick(namespace, id) if up_to_date_result == LoadBalancer::ALL_CAUGHT_UP
up_to_date_result != LoadBalancer::NONE_CAUGHT_UP
else
# Some callers want to err on the side of caution and be really sure that a caught up replica was
# found. If we did not have any location to check then we must force `use_primary!` if they they
# use_primary_on_empty_location
!use_primary_on_empty_location
end
::Gitlab::Database::LoadBalancing::Session.current.use_primary! if !result && use_primary_on_failure
result
end
# Starts sticking to the primary for the given namespace and id, using
# the latest WAL pointer from the primary.
def stick(namespace, id)
with_primary_write_location do |location|
set_write_location_for(namespace, id, location)
end
::Gitlab::Database::LoadBalancing::Session.current.use_primary!
end
def bulk_stick(namespace, ids)
with_primary_write_location do |location|
ids.each do |id|
set_write_location_for(namespace, id, location)
end
end
::Gitlab::Database::LoadBalancing::Session.current.use_primary!
end
private
def with_primary_write_location
# When only using the primary, there's no point in getting write
# locations, as the primary is always in sync with itself.
return if @load_balancer.primary_only?
location = @load_balancer.primary_write_location
return if location.blank?
yield(location)
end
def unstick(namespace, id)
with_redis do |redis|
redis.del(redis_key_for(namespace, id))
end
end
def set_write_location_for(namespace, id, location)
with_redis do |redis|
redis.set(redis_key_for(namespace, id), location, ex: EXPIRATION)
end
end
def last_write_location_for(namespace, id)
with_redis do |redis|
redis.get(redis_key_for(namespace, id))
end
end
def redis_key_for(namespace, id)
name = @load_balancer.name
"database-load-balancing/write-location/#{name}/#{namespace}/#{id}"
end
def with_redis(&block)
Gitlab::Redis::DbLoadBalancing.with(&block)
end
end
end
end
end
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