During profiling looking up topic users popped up as a hot path, this
change more than halved the amount of work it does
It reduces object allocations and method calls and avoids repeate translation
of common terms
This adds support for DISCOURSE_ENABLE_PERFORMANCE_HTTP_HEADERS
when set to `true` this will turn on performance related headers
```text
X-Redis-Calls: 10 # number of redis calls
X-Redis-Time: 1.02 # redis time in seconds
X-Sql-Commands: 102 # number of SQL commands
X-Sql-Time: 1.02 # duration in SQL in seconds
X-Queue-Time: 1.01 # time the request sat in queue (depends on NGINX)
```
To get queue time NGINX must provide: HTTP_X_REQUEST_START
We do not recommend you enable this without thinking, it exposes information
about what your page is doing, usually you would only enable this if you
intend to strip off the headers further down the stream in a proxy
Previously as soon as any override was defined we would regress to the slow
path for locale lookups. Additionally if `raise: true` was specified which
rails likes to add in views we would bypass the cache
The new design manages to use the fast path for many more cases
Before the locking here was added, replying to a post and liking a post
at roughly the same time could cause a deadlock.
Liking a post grabs an update lock on the post and then on the topic (to
update like counts).
We now lock the replied to post before getting the topic lock so that we
can update the replied to post later without causing a deadlock.
The site settings beginning with "topic views heat" and "topic post like
heat" are set to defaults when installing Discourse, but there has not
been a process or guidance for updating these values based on
community activity.
This feature will update them once a month. The low, medium, and
high settings will be based on the minimums of the 45th, 25th, and
10th percentile topics respectively, so that 45% of topics will have
some "heat".
Disable automatic changes with the automatic_topic_heat_values setting.
This does two things
1. Our "index grace period" has been wound down to 1 day, there is no point
keeping a bloated index for a week, usually when people delete stuff they
mean for it to be removed
2. We were never dropping deleted posts from the index, only posts from
deleted topics
These changes speed up search a tiny bit and reduce background work.
