Introduction

• Logs all cache tag invalidations.
• Sends cache tag invalidations to New Relic as Custom Events. Visualize and Analyze via New Relic Insights.
• Sends cache hits/misses to New Relic as Custom Events.

See the images that are attached to https://www.drupal.org/project/cache_metrics for example reports.

Per environment customization

In general, sites want this module enabled in Production and not on development environments. You can do that in Drupal 8.8+ with https://www.drupal.org/node/3079028.

Container parameters

This module is configured by container parameters (i.e. in a services,yml file). You can customize cache_metrics.new_relic.invalidations and cache_metrics.bins.blacklist. A blacklist value of '*' effectively disables cache hit/miss logging.

New Relic Insights

The default reporting tool is New Relic Insights. Some example NRQL

Cache Miss %

Shown as a table, displays the percentage of cache misses over all cache gets as well as the raw number of cache misses, faceted by cache bin.

SELECT
  ROUND((SUM(miss)/SUM(miss+hit))*100) AS 'Miss %',
  SUM(miss) AS 'Misses'
FROM CacheGet
FACET bin

Cache Hit %

Shown as a line graph, displays the cache hit percentage overtime faceted by cache bin.

SELECT
  ROUND((SUM(hit)/SUM(miss+hit))*100) AS 'Hit %'
FROM CacheGet
FACET bin
TIMESERIES LIMIT 40

Tag invalidations Over Time

Shown as an area graph, displays the raw number of tag invalidations grouped by tag name over time. This is useful for surfacing problematic tags (looking at you node_list). It's also useful for showing patterns of editorial activity.

SELECT
  count(tag)
FROM InvalidateTag
FACET tag
TIMESERIES
LIMIT 20

Raw tag invalidation counts

Shown as a pie chart, displays the number of cache invalidations faceted by cache tag. This is useful for targeting highly active cache tags that are know to be problematic (still looking at you node_list).

SELECT
  count(tag)
FROM InvalidateTag
FACET tag
LIMIT 20

URIs triggering invalidation

Shown as a pie chart, displays URIs on the site that are responsible for the most tag invalidations. When paired with logs and understanding what types of content appear here, can surface areas to target for optimization. Common culprits, perhaps unsurprisingly, are /node/add/ and /node/edit/.

SELECT
  count(uri) as 'Invalidations'
FROM InvalidateTag
FACET uri
LIMIT 8

Using an alternative analytics provider

In order to use something other than New Relic custom events,

1. Override the cache_metrics.cache_factory service. Change the isEnabled() method as needed, and also change the get() method to instantiate a different CacheBackendWrapper class. That class can extend this module's CacheBackendWrapper and override the record() method.
2. Override the cache_metrics.invalidator service and change the isEnabled() and record() methods to log elsewhere.

Reducing voluminous data logging

The hit/miss cache logging from this module can generate many thousands of events per minute on a popular site. Since the New Relic daemon buffers these events and send them every minute, this does not affect page performance. If you exceed NR limits, the daemon will automatically start sampling.

This module defaults to omitting cache gets to the config and discovery bins. Additional bins may be blacklisted via a service parameter.