This greatly improves the performance of Project#external_issue_tracker
by moving most of the fields queried in Ruby to the database and letting
the database handle all logic. Prior to this change the process of
finding an external issue tracker was along the lines of the following:
1. Load all project services into memory.
2. Reduce the list to only services where "issue_tracker?" returns true
3. Reduce the list from step 2 to service where "default?" returns false
4. Find the first service where "activated?" returns true
This has to two big problems:
1. Loading all services into memory only to reduce the list down to a
single item later on is a waste of memory (and slow timing wise).
2. Calling Array#select followed by Array#reject followed by Array#find
allocates extra objects when this really isn't needed.
To work around this the following service fields have been moved to the
database (instead of being hardcoded):
* category
* default
This in turn means we can get the external issue tracker using the
following query:
SELECT *
FROM services
WHERE active IS TRUE
AND default IS FALSE
AND category = 'issue_tracker'
AND project_id = XXX
LIMIT 1
This coupled with memoizing the result (just as before this commit)
greatly reduces the time it takes for Project#external_issue_tracker to
complete. The exact reduction depends on one's environment, but locally
the execution time is reduced from roughly 230 ms to only 2 ms (= a
reduction of almost 180x).
Fixes gitlab-org/gitlab-ce#10771