The ShardSelector
Middleware
provides a framework for automatically swapping shards. Rails provides a basic framework to determine which shard to switch to and allows for applications to write custom strategies for swapping if needed.
The ShardSelector
takes a set of options (currently only `lock` is supported) that can be used by the middleware to alter behavior. `lock` is true by default and will prohibit the request from switching shards once inside the block. If `lock` is false, then shard swapping will be allowed. For tenant based sharding, `lock` should always be true to prevent application code from mistakenly switching between tenants.
Options can be set in the config:
config.active_record.shard_selector = { lock: true }
Applications must also provide the code for the resolver as it depends on application specific models. An example resolver would look like this:
config.active_record.shard_resolver = ->(request) { subdomain = request.subdomain tenant = Tenant.find_by_subdomain!(subdomain) tenant.shard }
# File activerecord/lib/active_record/middleware/shard_selector.rb, line 30 def initialize(app, resolver, options = {}) @app = app @resolver = resolver @options = options end
# File activerecord/lib/active_record/middleware/shard_selector.rb, line 38 def call(env) request = ActionDispatch::Request.new(env) shard = selected_shard(request) set_shard(shard) do @app.call(env) end end
© 2004–2021 David Heinemeier Hansson
Licensed under the MIT License.