Module: CacheStache::Instrumentation

Defined in:
lib/cache_stache/instrumentation.rb

Constant Summary collapse

INTERNAL_OPERATION_KEY =

Thread-local key to track when CacheStache is performing internal operations

:cache_stache_internal_operation
AFTER_REPLY_QUEUE_KEY = 
:cache_stache_after_reply_queue
MAX_AFTER_REPLY_EVENTS = 
1000

Class Attribute Summary collapse

Class Method Summary collapse

Class Attribute Details

.monitored_store_class ⇒ Object (readonly)

Returns the value of attribute monitored_store_class.



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# File 'lib/cache_stache/instrumentation.rb', line 11

def monitored_store_class
  @monitored_store_class
end

Class Method Details

.call(_name, _start, _finish, _id, payload) ⇒ Object 



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# File 'lib/cache_stache/instrumentation.rb', line 55

def call(_name, _start, _finish, _id, payload)
  # Skip if this is an internal CacheStache operation
  return if internal_operation?

  # Only track events from Rails.cache, not other ActiveSupport::Cache instances
  return unless payload[:store] == @monitored_store_class

  key = payload[:key] || payload[:name]
  return unless key
  # Belt-and-suspenders: also skip by key prefix in case thread-local wasn't set
  return if key.to_s.start_with?("cache_stache:")

  # Skip event based on sample_rate (e.g., 0.5 means record 50% of events)
  sample_rate = CacheStache.configuration.sample_rate
  return if sample_rate < 1.0 && rand >= sample_rate

  # Record hit or miss
  bucket_ts = (Time.current.to_i / CacheStache.configuration.bucket_seconds) * CacheStache.configuration.bucket_seconds
  hit = payload[:hit]

  increments = {
    "overall:hits" => hit ? 1 : 0,
    "overall:misses" => hit ? 0 : 1
  }

  # Add keyspace increments
  matching_keyspaces = CacheStache.configuration.matching_keyspaces(key)
  matching_keyspaces.each do |keyspace|
    increments["#{keyspace.name}:hits"] = hit ? 1 : 0
    increments["#{keyspace.name}:misses"] = hit ? 0 : 1
  end

  # Filter out zero-valued fields to reduce write amplification
  increments.reject! { |_k, v| v == 0 }

  if should_defer_instrumentation?
    enqueue_after_reply_event(bucket_ts, increments)
  else
    @cache_client.increment_stats(bucket_ts, increments)
  end
rescue => e
  Rails.logger.error("CacheStache instrumentation error: #{e.class}: #{e.message}")
  Rails.logger.error(e.backtrace.first(5).join("\n"))
end

.flush_after_reply_queue! ⇒ Object 



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# File 'lib/cache_stache/instrumentation.rb', line 100

def flush_after_reply_queue!
  return unless @cache_client
  queue = Thread.current[AFTER_REPLY_QUEUE_KEY]
  return unless queue.is_a?(Array) && !queue.empty?

  max = MAX_AFTER_REPLY_EVENTS
  dropped = [queue.size - max, 0].max
  events = queue.shift([queue.size, max].min)
  queue.clear

  Rails.logger.warn("CacheStache: Dropped #{dropped} after-reply events") if dropped.positive?

  combined = {}
  events.each do |(bucket_ts, increments)|
    combined[bucket_ts] ||= Hash.new(0)
    increments.each do |field, value|
      combined[bucket_ts][field] += value
    end
  end

  combined.each do |bucket_ts, increments|
    # Filter out zero-valued fields to reduce write amplification
    increments.reject! { |_k, v| v == 0 }
    @cache_client.increment_stats(bucket_ts, increments)
  end
rescue => e
  Rails.logger.error("CacheStache after-reply flush error: #{e.class}: #{e.message}")
  Rails.logger.error(e.backtrace.first(5).join("\n"))
end

.install! ⇒ Object 



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# File 'lib/cache_stache/instrumentation.rb', line 19

def install!
  return unless CacheStache.configuration.enabled
  return if @installed

  # Store cache_client as a class instance variable
  @cache_client = CacheClient.new
  @cache_client.store_config_metadata

  # Capture the Rails.cache store class name to filter events.
  # Note: This filters by class name, not instance. If multiple stores
  # use the same class (e.g., two RedisCacheStore instances), events
  # from all of them will be tracked.
  @monitored_store_class = Rails.cache.class.name

  # Subscribe to cache read events only (hits and misses)
  ActiveSupport::Notifications.subscribe("cache_read.active_support", self)

  @installed = true
  Rails.logger.info("CacheStache: Instrumentation installed for #{@monitored_store_class}")
end

.internal_operation? ⇒ Boolean

Returns true if we’re currently inside an internal CacheStache operation

Returns:

  • (Boolean) 


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# File 'lib/cache_stache/instrumentation.rb', line 51

def internal_operation?
  Thread.current[INTERNAL_OPERATION_KEY] == true
end

.reset! ⇒ Object 



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# File 'lib/cache_stache/instrumentation.rb', line 13

def reset!
  @installed = false
  @monitored_store_class = nil
  @cache_client = nil
end

.without_instrumentation ⇒ Object

Execute a block while marking it as an internal CacheStache operation. Cache operations inside this block will be ignored by instrumentation.



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# File 'lib/cache_stache/instrumentation.rb', line 42

def without_instrumentation
  previous_value = Thread.current[INTERNAL_OPERATION_KEY]
  Thread.current[INTERNAL_OPERATION_KEY] = true
  yield
ensure
  Thread.current[INTERNAL_OPERATION_KEY] = previous_value
end