class Hoodoo::TransientStore::MemcachedRedisMirror
Hoodoo::TransientStore
plugin supporting storage into both Memcached and Redis simultaneously.
The implementation uses Hoodoo::TransientStore::Memcached
and Hoodoo::TransientStore::Redis
to talk to the two storage engines.
When looking up data with get
, the requested item must be found in both storage engines. If it is found in only one, the other one is deleted to keep maximum pool space available in both and nil
will be returned for the lookup.
Note unusual requirements for the connection URI data provided to the initialize call.
The mirroring storage engine plug-in is useful if migrating from one of these engines to another without invalidating data present in the one from which you are migrating away. Change to using the mirrored storage engine for as long as the maximum item expiry period in the old engine, then once you know all old engine items must have been expired, cut over to just the new engine.
Attributes
Command an instance to allow get
to return values which are only found in one or the other storage engine, or in both.
Permitted values are:
:memcached
-
Only
Memcached
needs to have a value for a key :redis
-
Only
Redis
needs to have a value for a key both
-
Both engines must have the key
This is useful in migration scenarios where moving from Memcached
to Redis
or vice versa. If wishing to be able to still read old data only in Memcached
, set :memcached
; else :redis
. That way, data only in the old engine but not yet in the new is still considered valid and read back. For true mirroring which requires both stores to have the value, use :both
.
The default is :both
.
Public Class Methods
See Hoodoo::TransientStore::Base::new
for details.
Do not instantiate this class directly. Use Hoodoo::TransientStore::new
.
The storage_host_uri
parameter is necessarily unusual here. It must be either _a Hash_ with Symbol keys :memcached
and :redis
, or a serialised JSON string representing the same information. These values define the actual storage engine host URI for the respective engines. For example, to connect to locally running engines configured on their default ports, pass this Hash in storage_host_uri
:
{ :memcached => 'localhost:11211', :redis => 'redis://localhost:6379' }
…or:
"{
\"memcached\": \"localhost:11211\",
\"redis\": \"redis://localhost:6379\"
}"
See Hoodoo::TransientStore::Memcached::new
and Hoodoo::TransientStore::Redis::new
for details of connection URI requirements for those engines.
The value of the namespace
parameter applies equally to both engines.
Hoodoo::TransientStore::Base::new
# File lib/hoodoo/transient_store/transient_store/memcached_redis_mirror.rb, line 88 def initialize( storage_host_uri:, namespace: ) super # Pass all arguments through -> *not* 'super()' storage_host_uri = deserialize_and_symbolize( storage_host_uri ) if storage_host_uri.is_a?( String ) unless storage_host_uri.is_a?( Hash ) && storage_host_uri.has_key?( :memcached ) && storage_host_uri.has_key?( :redis ) raise 'Hoodoo::TransientStore::MemcachedRedisMirror: Bad storage host URI data passed to constructor' end @get_keys_from = :both @memcached_store = Hoodoo::TransientStore::Memcached.new( storage_host_uri: storage_host_uri[ :memcached ], namespace: namespace ) @redis_store = Hoodoo::TransientStore::Redis.new( storage_host_uri: storage_host_uri[ :redis ], namespace: namespace ) end
Public Instance Methods
See Hoodoo::TransientStore::Base#close
for details.
# File lib/hoodoo/transient_store/transient_store/memcached_redis_mirror.rb, line 178 def close @memcached_store.close() rescue nil # Rescue so that Redis "close()" is still attempted. @redis_store.close() end
See Hoodoo::TransientStore::Base#delete
for details.
# File lib/hoodoo/transient_store/transient_store/memcached_redis_mirror.rb, line 152 def delete( key: ) exception = nil begin @memcached_store.delete( key: key ) rescue => e exception = e end # But allow Redis delete to still be attempted... begin @redis_store.delete( key: key ) rescue => e exception ||= e end if exception.nil? return true else raise exception end end
See Hoodoo::TransientStore::Base#get
for details.
The requested item must be found in both Memcached
and Redis
. If it is found in only one, the other one is deleted to keep maximum pool space available in and nil
will be returned.
If get_keys_from
is configured for :both
and the data for some reason has ended up differing in the two stores - most likely because something modified just one of them (perhaps there is outdated code kicking around which is writing to just one) - then the Memcached
copy will “win” and the Redis
value will be ignored.
# File lib/hoodoo/transient_store/transient_store/memcached_redis_mirror.rb, line 125 def get( key: ) case @get_keys_from when :both memcached_result = @memcached_store.get( key: key ) redis_result = @redis_store.get( key: key ) if @get_keys_from == :both && ( memcached_result.nil? || redis_result.nil? ) delete( key: key ) return nil else return memcached_result end when :memcached return @memcached_store.get( key: key ) when :redis return @redis_store.get( key: key ) else raise "Hoodoo::TransientStore::Base\#get: Invalid prior value given in \#get_keys_from= of '#{ @get_keys_from.inspect }' - only ':both', ':memcached' or ':redis' are allowed" end end
See Hoodoo::TransientStore::Base#set
for details.
# File lib/hoodoo/transient_store/transient_store/memcached_redis_mirror.rb, line 106 def set( key:, payload:, maximum_lifespan: ) memcached_result = @memcached_store.set( key: key, payload: payload, maximum_lifespan: maximum_lifespan ) redis_result = @redis_store.set( key: key, payload: payload, maximum_lifespan: maximum_lifespan ) return memcached_result && redis_result end