The sum of a page's tags' invalidation counters, which is Drupal's own freshness test.
Drupal's DatabaseCacheTagsChecksum compares a stored checksum against this same sum, so a page
whose sum has not moved was not invalidated. Compared at serve time it trades a write per
affected page for a read per served page (free allows 5,000,000 rows read a day against 100,000
written). Zero for a page with no recorded tags, which is not a usable checksum; callers must
tell that case apart.
The sum of a page's tags' invalidation counters, which is Drupal's own freshness test.
Drupal's
DatabaseCacheTagsChecksumcompares a stored checksum against this same sum, so a page whose sum has not moved was not invalidated. Compared at serve time it trades a write per affected page for a read per served page (free allows 5,000,000 rows read a day against 100,000 written). Zero for a page with no recorded tags, which is not a usable checksum; callers must tell that case apart.