First implementation of FIFO/Stacked.
parent
d46e0d2ddf
commit
b38e3f31ba
|
@ -1,4 +1,5 @@
|
|||
require "file_utils"
|
||||
require "json"
|
||||
|
||||
require "./fifo.cr" # FIFO class to implement a cache policy.
|
||||
require "./dodb/*" # Databases and indexes (basic indexes, partitions, tags, etc.).
|
||||
|
|
|
@ -57,19 +57,18 @@ class DODB::Storage::Cached(V) < DODB::Storage(V)
|
|||
end
|
||||
end
|
||||
|
||||
# Getting data from the hash in RAM.
|
||||
# Gets data from the hash in RAM.
|
||||
def []?(key : Int32) : V?
|
||||
@data[key]
|
||||
rescue e
|
||||
# FIXME: rescues any error the same way.
|
||||
return nil
|
||||
self[key] rescue nil
|
||||
end
|
||||
|
||||
# :inherit:
|
||||
# Gets the data with the *key*.
|
||||
# In case the data is missing, returns an exception `DODB::MissingEntry`.
|
||||
#
|
||||
# Data needs to be cloned in case it will be modified, otherwise it will mess with indexes.
|
||||
#
|
||||
# WARNING: data isn't cloned.
|
||||
# WARNING: may raise a MissingEntry exception.
|
||||
def [](key : Int32) : V
|
||||
@data[key] rescue raise MissingEntry.new(key)
|
||||
end
|
||||
|
|
|
@ -1,15 +1,53 @@
|
|||
# Stacked database: only recently requested entries are kept in memory.
|
||||
#
|
||||
# Most recently used entries are in cache and put on the top of the stack.
|
||||
# Least recently used entries may be removed from the cache in order to keep the amount of memory used reasonable.
|
||||
#
|
||||
# This database is relevant for high demand applications;
|
||||
# which means both a high number of entries (data cannot fit entirely in RAM),
|
||||
# and a high number of requests.
|
||||
# Typically a retail website.
|
||||
# In such applications, the "keep the most recently used data in cache" policy works since new users
|
||||
# constantly push commonly requested data on top of the stack.
|
||||
#
|
||||
# ```
|
||||
# # Creates a DODB stacked database.
|
||||
# car_database = DODB::Storage::Stacked.new "/path/to/db"
|
||||
#
|
||||
# # Creates a (cached) index.
|
||||
# cars_by_name = car_database.new_index "name", &.name
|
||||
#
|
||||
# # Add a value in the database.
|
||||
# car_database << Car.new "Corvet"
|
||||
# ```
|
||||
# On the file-system:
|
||||
# ```plain
|
||||
# storage
|
||||
# ├── data
|
||||
# │ └── 0000000000
|
||||
# ├── indices
|
||||
# │ └── by_name <- the "name" basic index
|
||||
# │ └── Corvet -> ../../data/0000000000
|
||||
# ```
|
||||
#
|
||||
# NOTE: fast for frequently requested data and requires a stable (and configurable) amount of memory.
|
||||
# TODO: not yet implemented.
|
||||
class DODB::Storage::Stacked(V) < DODB::Storage::Cached(V)
|
||||
# The maximum number of accepted entries in the cache.
|
||||
property max_entries : Int32
|
||||
# The *stack* a simple FIFO instance where the key of the requested data is pushed.
|
||||
# In case the number of stored entries exceeds what is allowed, the least recently used entry is removed.
|
||||
property stack : FIFO(Int32)
|
||||
|
||||
# Initializes the `StackedDataBase` with a maximum number of entries in the cache.
|
||||
def initialize(directory_name : String, @max_entries : Int32 = 100_000)
|
||||
super directory_name
|
||||
@stack = FIFO(Int32).new @max_entries
|
||||
end
|
||||
|
||||
def [](key : Int32) : V
|
||||
val = @data[key] rescue raise MissingEntry.new(key)
|
||||
if entry_to_remove = @stack << key
|
||||
@data.delete entry_to_remove
|
||||
end
|
||||
val
|
||||
end
|
||||
end
|
||||
|
|
Loading…
Reference in New Issue