Reducing repeated queries.
WHAT IT IS
Storing the results of database queries in memory, so repeated identical queries do not hit the database.
Distinct from page caching, which stores whole rendered pages.
WHY IT HELPS
A page running four hundred queries, many of them identical across requests, benefits enormously.
Particularly useful for logged-in traffic and for shops, where page caching cannot apply.
WHAT PROVIDES IT
Redis or Memcached, where available on your plan.
Some applications also have a file-based object cache, which is slower and still better than nothing.
CHECKING AVAILABILITY
Open a ticket and ask what is available on your plan. It varies.
CONFIGURING IT
A plugin connects the application to the cache. WordPress requires a drop-in file that the plugin installs.
WHAT TO WATCH
Stale data. A cache serving an outdated value after a change is the usual complaint.
Flush the object cache after configuration changes.
THE ORDER OF PRIORITY
Page caching first, since it eliminates the request entirely. Object caching second, for what page caching cannot cover.
