How to monitor warmers efficiency
To assess the efficiency of the Page Cache Warmer, use the Statistical info block. To determine the current cache fill, use the Effective cache fill rate. To check how many pages were served from the cache when visited in the browser during the last 24 hours, use the Cache coverage (last 24h) line. To see how the cache fill has changed over the past 24 hours, use the Cache fill history graph. The average warming speed and cache type can be seen in Server info block.
Cache clearance by TTL
When the cache is cleared by TTL, the cache for a small group of pages is cleared and refilled, which can be seen on the chart as slight fluctuations along the horizontal line.
By default, the cache clearance frequency by TTL is 24 hours (86400 seconds). You can change the TTL in Stores -> Configuration -> Advanced -> System -> Full Page Cache -> TTL for public content.
Full page cache clearance
With manual cache clearing, there is a sharp drop on the chart over a short period of time. A similar graph will appear, for example, when Magento clears the cache after adding a new store view, importing new products, or performing another action that requires cache clearing and indexing.
If the site has many pages, cache clearing may occur in stages, which is expected behavior.
Cache clearance after page updates
By default, the extension tracks changes to products and other pages on the site and updates the cache after they are saved. The chart will look like the one shown below. The height and length of the peaks will depend on the number of URLs processed by your server.
To prevent unwanted cache flushes, enable the Forbid cache flushing option in the Caching and behavior settings. Cache clearance followed by refilling can also be triggered by Magento or third-party extensions. If enabling Forbid cache flushing did not stop cache clearing, check the default Magento logs to identify the cause.
Small number of cached pages
A low fill history level may occur if:
- Cron runs too infrequently. Increasing the frequency of cron jobs can increase the number of cached pages.
- There are too many URLS in Pages. Prioritize to warm only really popular pages.
- Conditions in Warm rules limit the number of pages being warmed. Review the rules and create additional rules if necessary.
- The cache is cleared too frequently. Use Cache flushes to identify the cause of cache clearing and reduce its frequency.
- There are non-cacheable blocks on the page or pages. Enable Forcibly make pages cacheable.
The fill history can also be affected by the Warming strategy and Warming Level. Try adjusting them to achieve better results.