Caching

Heavy expressions (i.e. refering to several thousands of series) have long run times to compute.

The @cached:ttl(,resetTtl,invalidate) operator provides a means to store the results of expressions for a specified time to live (ttl). This way, you may access results of heavy expressions without the computational overhead. The maximum ttl is 24 hours. The @cached request stores and returns points based on the df/dt which was used.

Note that when relative dates like -1d or -5M are used for df/dt the requested date range will differ each time the request is made and the cached result may not be returned. Therefore, appending a 'b' to relative dates like -1db or -5Mb is recommended. See Date Input Notation for more info.  To maximize the chances of the cache being used, use MIN/MAX for df/dt. invalidate:The expression is only run if it's not cached.  This means if the result is within the ttl (time-to-live), it will not be re-run.  To force a rerun, use the optional invalidate keyword.  This forces the invalidation of the values in the cache. resetTtloverrides the ttl from the current time.  For example, calling @cached:20h at 00:00 will cache until 20:00.  Calling @cached:20h,resetTtl at 01:00 will reset the ttl to 21:00.

Example usage:

• The first @cached run should include :ttl in order to specify the lifetime of the cached result.
• At 00:00 =x@cached is run.  This does not hit the cache because it has never been cached before.  The expression is executed.
• At 01:00 =x@cached:5h is run.  This caches until 06:00. The expression is executed.
• At 01:10 =x@cached is run.  This retrieves from the cache (cache hit!), so the expression is not executed.
• At 03:30 =x@cached:5h is run.  This retrieves from the cache (cache hit) and does not change the ttl. ttl is still 06:00.
• At 06:15 =x@cached:5h is run.  This re-executes (no cache hit) because we are beyond the ttl and it sets the new ttl to be 11:15.
• At 10:00 =x@cached:5h,resetTtl is run.  This retrieves from the cache (cache hit) and moves the ttl to 15:00 without re-executing.
• At 11:30 =xis run.  This does not even try to get the cached values.  The expression is executed.
• At 11:00 =x@cached:5h,invalidate is run.  This re-executes the expression and caches the new values because we used the invalidate flag but keeps the ttl the same (15:00).
• At 12:00 =x@cached:5h,invalidate,resetTtl is run.  This re-executes because we used the invalidate flag and also moves the ttl to 17:00.