CODEWITHSUNDEEP
node.jsexpressrediscoordinates
César Bergamaschi
César Bergamaschi

Reputation: 21

Store and retrieve data from coordinates in Redis

I'm using Redis as a caching system to store data to avoid unnecessary consume on an API. What i was thinking is after get the result from the API, store the coordinate (as a key, for example) and the data on Redis and in a later search before consume the external api again, passing the a new coordinate check in Redis if matches with the saved coordinate (in meters, or anything) and if it matches, bring me the data stored.

I already searched for at least 1 hour and could not find any relevant results that fits my needs. For example, GEOADD could not help me because it doesn't expire automatically by Redis.

The only solution would be storing the coordinates as key (example: -51.356156,-50.356945) with a json value, and check with a functional programming all the keys (coordinates) if it's matches with an other coordinate. But it seens not elegant, also with bad performance.

Any ideas?

I'm using Redis in NodeJS (Express).

Upvotes: 1

Views: 735

Answers (1)

Itamar Haber
Itamar Haber

Reputation: 50052

If I understand correctly, you want to able to:

  1. Cache the API's response for a given tuple of coordinates
  2. Be able to perform an efficient radius search over the cached responses
  3. Use Redis' expiration to invalidate old cache entries

To satisfy #1, you've already outlined the right approach - store each API call under its own key. You can name the key by your coordinates, or use their geohash value (computing it can be done in the client or with a temporary element in Redis). Also don't forget setting a TTL on that key and the global maxmemory eviction policy for eviction to actually work.

The 2nd requirement calls for using a Geo Set. Store the coordinates and the key names in it. Perform your query by calling GEORADIUS and then fetch the relevant keys according to the reply.

While fetching the keys from #2's query, you may find some of them have been evicted from the keyspace but not in the Geo Set. Call ZREM for each of these to keep a semblance of sync between your index (the Geo Set) and the keyspace. Additionally, you can also run a periodic background task that ZSCAN's the Geo Set and does housekeeping. That should take care of #3.

Upvotes: 1

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