Speed up public stream and remove obsolete indexes

[CSammy]

Speeds up the public stream by a factor of 1000 on a production PostgreSQL database, it's lightning fast now. MySQL shows improvement as well.

[goobertron]

Whaouh – I can't test this, but this could be BIG. Sharing some love for this.

[SuperTux88]

Looks good to me, also improves MySQL performance by a factor of 10 on an old export of my prod DB on my dev-pod. Thanks for the analysis 🍪 Migration took around 15s on my dev-pod with MySQL, so should be OK for a minor release.

[SuperTux88]

Merged as a21cde4

Thanks again @CSammy 🍪

@goobertron you can now test the speed of it on the HQ-pod :)

[Flaburgan]

\o/ Now, to the user stream! 😛

[goobertron]

@goobertron you can now test the speed of it on the HQ-pod :)

I also haven't noticed a dramatic improvement on the HQ pod. From manual timing of how long the 'spinning wheel' is present, it's 7 seconds on the /public stream versus 9 seconds on the main /stream.

[koehn]

Ahh, I thought this was about the /stream query based on a conversation online. My bad; disregard my earlier comments.

[koehn]

Looking into the explain of the stream query, it's doing a full table scan on posts because created_at is a timestamp without time zone. Is there any reason we don't have a time zone on these columns?

[Stivovo]

/db/migrate/20181227235201_clean_up_posts_indexes.rb