8b5f64881c
After all our recent troubles with DBM I figured I'd benchmark the performance of DBM vs. JSON. At read time (what we care more about) the performance is pretty much identical and JSON is only 1.5x slower at write time. This seems worth it for the reliability increases to avoid messing with unreliable native code.
124 lines
2.6 KiB
Ruby
124 lines
2.6 KiB
Ruby
require "json"
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#
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# `CacheStoreDatabase` acts as an interface to a persistent storage mechanism
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# residing in the `HOMEBREW_CACHE`
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#
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class CacheStoreDatabase
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# Yields the cache store database.
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# Closes the database after use if it has been loaded.
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#
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# @param [Symbol] type
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# @yield [CacheStoreDatabase] self
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def self.use(type)
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database = CacheStoreDatabase.new(type)
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return_value = yield(database)
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database.close_if_open!
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return_value
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end
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# Sets a value in the underlying database (and creates it if necessary).
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def set(key, value)
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db[key] = value
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end
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# Gets a value from the underlying database (if it already exists).
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def get(key)
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return unless created?
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db[key]
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end
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# Gets a value from the underlying database (if it already exists).
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def delete(key)
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return unless created?
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db.delete(key)
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end
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# Closes the underlying database (if it is created and open).
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def close_if_open!
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return unless @db
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cache_path.atomic_write(JSON.dump(@db))
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end
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# Returns `true` if the cache file has been created for the given `@type`
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#
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# @return [Boolean]
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def created?
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cache_path.exist?
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end
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private
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# Lazily loaded database in read/write mode. If this method is called, a
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# database file with be created in the `HOMEBREW_CACHE` with name
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# corresponding to the `@type` instance variable
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#
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# @return [Hash] db
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def db
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@db ||= begin
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JSON.parse(cache_path.read) if created?
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rescue JSON::ParserError
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nil
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end
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@db ||= {}
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end
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# Creates a CacheStoreDatabase
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#
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# @param [Symbol] type
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# @return [nil]
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def initialize(type)
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@type = type
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end
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# The path where the database resides in the `HOMEBREW_CACHE` for the given
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# `@type`
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#
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# @return [String]
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def cache_path
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HOMEBREW_CACHE/"#{@type}.json"
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end
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end
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#
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# `CacheStore` provides methods to mutate and fetch data from a persistent
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# storage mechanism
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#
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class CacheStore
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# @param [CacheStoreDatabase] database
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# @return [nil]
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def initialize(database)
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@database = database
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end
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# Inserts new values or updates existing cached values to persistent storage
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# mechanism
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#
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# @abstract
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def update!(*)
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raise NotImplementedError
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end
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# Fetches cached values in persistent storage according to the type of data
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# stored
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#
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# @abstract
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def fetch_type(*)
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raise NotImplementedError
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end
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# Deletes data from the cache based on a condition defined in a concrete class
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#
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# @abstract
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def flush_cache!
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raise NotImplementedError
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end
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protected
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# @return [CacheStoreDatabase]
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attr_reader :database
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end
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