Master-Replica databases result in multiple cached entities. #135
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langal
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Aug 15, 2019
noripyt#135 Have the table key generation look for a "CACHE_KEY" configuration in the Django DATABASES configs. If a "CACHE_KEY" value is found, then we use that instead of the "db_alias". This allows us to synch Master and Replicas to use the same key namespace to prevent "double-caching" and the need to invalidate 2 cache entries upon an update. The Django configuration would look like: DATABASES = { 'master': { 'CACHE_KEY': 'WE_ARE_ONE', 'ENGINE': 'django.db.backends.postgresql_psycopg2', 'NAME': DB_NAME, 'USER': DB_USER, 'PASSWORD': DB_PASSWORD, 'HOST': DB_HOST, 'PORT': DB_PORT, 'OPTIONS': { 'client_encoding': "UTF8" } }, 'replica' : { 'CACHE_KEY': 'WE_ARE_ONE', 'ENGINE': 'django.db.backends.postgresql_psycopg2', 'NAME': DB_NAME, 'USER': DB_USER, 'PASSWORD': DB_PASSWORD, 'HOST': DB_HOST, 'PORT': DB_PORT, 'OPTIONS': { 'client_encoding': "UTF8" } } }
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If we have both a master and replica database configured, cachalot uses separate database aliases as part of the cache key.
This results in the same "data"being cached twice.
It also makes cache invalidation trickier as we have to invalidate multiple cached entries.
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