Question

THE INFO

Currently I have two tables I am working with- a POST table that holds data for a individual posts, and a FAVORITES table that holds data for users that opt to save favorite posts in their profile.

The tables look like this:

On the POSTS table there is only a primary key on id, no indexes that I have set. On Favorites I have a combined index that I was testing of (postid, deviceid).

The POSTS table contains approx. 10,000 entries.

The FAVORITES table contains approx. 4,680,500 entries.

The query I use to grab the favorites from a particular deviceid is:

SELECT post FROM POSTS 
WHERE id IN 
   (SELECT postid FROM favourites WHERE deviceid="12d4a4a4a4a4a4a");

THE PROBLEM:

With the amount of data being returned, and several devices having multiple favorites, the query can take upwards of 7-10 seconds to both COUNT favorites for a particular device and/or SELECT using the above query and subquery. When this happens during peak times, you can obviously imagine the issues that can cause.

Caching the query results is an option, but since the data is pretty specific in that the same user is not calling the query multiple times, but rather unique instances, I think there is a better solution. On another note, caching would need to be short lived, which would nullify its benefit.

I know the method of indexing, and I am familiar with foreign keys, but I’m not sure practically if and how they could be implemented between the query and the subquery to enhance performance.

Any advice/guidance is much appreciated.

Cheers,

Jared

Answer 1

SELECT post FROM POSTS 
INNER JOIN favourites ON POSTS.id=favourites.postid 
WHERE favourites.deviceid="12d4a4a4a4a4a4a");

split the index in favourites in 2 indices one on deviceid and one on postid