node server API request cache - persistent

[Don-Isdale]

Overview

So far memory-cache is used in node server to cache results of API requests which are common, e.g. zoomed-out requests for featuresCounts, blockFeaturesLimits, paths{,ViaAliases}.
HighDensity data means that db queries can be sufficiently long that persistence of this cache is desirable.
There are a number of options - see resources below; the simplest change is to use flat-cache in place of memory-cache.

Branch : feature/requestCachePersistent

Resources

Caching in database

• node-cache-manager-mongodb
  https://github.com/v4l3r10/node-cache-manager-mongodb#readme
  https://www.npmjs.com/package/cache-manager-mongodb

• https://github.com/BryanDonovan/node-cache-manager
  Storage engines include Redis, mongoDb, etc.

• overview of use of Redis to cache in mongoDb :
  https://www.sitepoint.com/caching-a-mongodb-database-with-redis/

Simple caches

• overview of use of memory-cache, flat-cache, memcached :
  https://scotch.io/tutorials/how-to-optimize-node-requests-with-simple-caching-strategies

---

• used flat-cache in place of memory-cache (wrapped with an equivalent api so they are swappable)
  feature/requestCachePersistent : 5268acd 6066269