debian-mirror-gitlab/lib/gitlab/repository_hash_cache.rb

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2020-03-09 13:42:32 +05:30
# frozen_string_literal: true
# Interface to the Redis-backed cache store for keys that use a Redis HSET.
# This is currently used as an incremental cache by the `Repository` model
# for `#merged_branch_names`. It works slightly differently to the other
# repository cache classes in that it is intended to work with partial
# caches which can be updated with new data, using the Redis hash system.
module Gitlab
class RepositoryHashCache
attr_reader :repository, :namespace, :expires_in
RepositoryHashCacheError = Class.new(StandardError)
InvalidKeysProvidedError = Class.new(RepositoryHashCacheError)
InvalidHashProvidedError = Class.new(RepositoryHashCacheError)
# @param repository [Repository]
# @param extra_namespace [String]
# @param expires_in [Integer] expiry time for hash store keys
def initialize(repository, extra_namespace: nil, expires_in: 1.day)
@repository = repository
@namespace = "#{repository.full_path}"
@namespace += ":#{repository.project.id}" if repository.project
@namespace = "#{@namespace}:#{extra_namespace}" if extra_namespace
@expires_in = expires_in
end
# @param type [String]
# @return [String]
def cache_key(type)
"#{type}:#{namespace}:hash"
end
# @param key [String]
# @return [Integer] 0 or 1 depending on success
def delete(key)
with { |redis| redis.del(cache_key(key)) }
end
# Check if the provided hash key exists in the hash.
#
# @param key [String]
# @param h_key [String] the key to check presence in Redis
# @return [True, False]
def key?(key, h_key)
with { |redis| redis.hexists(cache_key(key), h_key) }
end
# Read the values of a set of keys from the hash store, and return them
# as a hash of those keys and their values.
#
# @param key [String]
# @param hash_keys [Array<String>] an array of keys to retrieve from the store
# @return [Hash] a Ruby hash of the provided keys and their values from the store
def read_members(key, hash_keys = [])
raise InvalidKeysProvidedError unless hash_keys.is_a?(Array) && hash_keys.any?
with do |redis|
# Fetch an array of values for the supplied keys
values = redis.hmget(cache_key(key), hash_keys)
# Turn it back into a hash
hash_keys.zip(values).to_h
end
end
# Write a hash to the store. All keys and values will be strings when stored.
#
# @param key [String]
# @param hash [Hash] the hash to be written to Redis
# @return [Boolean] whether all operations were successful or not
def write(key, hash)
raise InvalidHashProvidedError unless hash.is_a?(Hash) && hash.any?
full_key = cache_key(key)
with do |redis|
results = redis.pipelined do
# Set each hash key to the provided value
hash.each do |h_key, h_value|
redis.hset(full_key, h_key, h_value)
end
# Update the expiry time for this hset
redis.expire(full_key, expires_in)
end
results.all?
end
end
# A variation on the `fetch` pattern of other cache stores. This method
# allows you to attempt to fetch a group of keys from the hash store, and
# for any keys that are missing values a block is then called to provide
# those values, which are then written back into Redis. Both sets of data
# are then combined and returned as one hash.
#
# @param key [String]
# @param h_keys [Array<String>] the keys to fetch or add to the cache
# @yieldparam missing_keys [Array<String>] the keys missing from the cache
# @yieldparam new_values [Hash] the hash to be populated by the block
# @return [Hash] the amalgamated hash of cached and uncached values
def fetch_and_add_missing(key, h_keys, &block)
# Check the cache for all supplied keys
cache_values = read_members(key, h_keys)
# Find the results which returned nil (meaning they're not in the cache)
missing = cache_values.select { |_, v| v.nil? }.keys
if missing.any?
new_values = {}
# Run the block, which updates the new_values hash
yield(missing, new_values)
# Ensure all values are converted to strings, to ensure merging hashes
# below returns standardised data.
new_values = standardize_hash(new_values)
# Write the new values to the hset
write(key, new_values)
# Merge the two sets of values to return a complete hash
cache_values.merge!(new_values)
end
record_metrics(key, cache_values, missing)
cache_values
end
private
def with(&blk)
Gitlab::Redis::Cache.with(&blk) # rubocop:disable CodeReuse/ActiveRecord
end
# Take a hash and convert both keys and values to strings, for insertion into Redis.
#
# @param hash [Hash]
# @return [Hash] the stringified hash
def standardize_hash(hash)
hash.map { |k, v| [k.to_s, v.to_s] }.to_h
end
# Record metrics in Prometheus.
#
# @param key [String] the basic key, e.g. :merged_branch_names. Not record-specific.
# @param cache_values [Hash] the hash response from the cache read
# @param missing_keys [Array<String>] the array of missing keys from the cache read
def record_metrics(key, cache_values, missing_keys)
cache_hits = cache_values.delete_if { |_, v| v.nil? }
# Increment the counter if we have hits
metrics_hit_counter.increment(full_hit: missing_keys.empty?, store_type: key) if cache_hits.any?
# Track the number of hits we got
metrics_hit_histogram.observe({ type: "hits", store_type: key }, cache_hits.size)
metrics_hit_histogram.observe({ type: "misses", store_type: key }, missing_keys.size)
end
def metrics_hit_counter
@counter ||= Gitlab::Metrics.counter(
:gitlab_repository_hash_cache_hit,
"Count of cache hits in Redis HSET"
)
end
def metrics_hit_histogram
@histogram ||= Gitlab::Metrics.histogram(
:gitlab_repository_hash_cache_size,
"Number of records in the HSET"
)
end
end
end