Query caches have historically used the last changed timestamp as a salt. While this has proven effective for most sites, it leads to an excessive number of caches which can be problematic on high-traffic and heavily updated sites. WordPress 6.9 introduces changes to how cache keys are created in order to ensure efficient use of object caches and help caches clean up after themselves.
These changes are compatible with existing implementations of persistent caching drop-ins. Vendors are not required to make any changes to their code to support these features in WordPress 6.9. As with other caching functions, the functions
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