What data is cached in Atlas, and what are the details.

[benbelow]

Question from @daria-sorokina-da

"Caching - what's cached? where? which types of caches (in-memory?)? how to invalidate?"

[zabeen]

A package called LazyCache is used extensively to provide in-memory caches.

Two types of cache length are configured: Transient and Persistent

Transient Cache

• Counter intuitively this cache has an incredibly long lifetime (~10 years)
• It is "transient" as it will only be registered as a transient dependency in DI - meaning a new one is created whenever we need it
• This cache is used for caching configuration values for which we need the data to be consistent across a request, even if it is not difficult to re-calculate
  • e.g. which matching database is currently active

Persistent Cache

• This cache persists across search requests, and expires once per day
• It is used for quickly looking up metadata without needing to make a request to a third party store (e.g. Azure Storage)
  • e.g. HLA Metadata dictionary - all tables are cached in memory for quick lookup
  • e.g. MAC dictionary
  • e.g. HF sets in match prediction
• If the data in this cache becomes out of date, a service restart of all affected functions apps is necessary to force cache regeneration
  • see Invalidate HMD caches when a new version of the same nomenclature is updated #745 for an update that would force cache invalidation for HMD updates, similar logic could be applied for other cached metadata