Use a specialized class for querying events

This changes various controllers to use the new EventCollection class
for retrieving events. This class uses a JOIN LATERAL query on
PostgreSQL to retrieve queries in a more efficient way, while falling
back to a simpler / less efficient query for MySQL.

The EventCollection class also includes a limit on the number of events
to display to prevent malicious users from cycling through all events,
as doing so could put a lot of pressure on the database.

JOIN LATERAL is only supported on PostgreSQL starting with version 9.3.0
and as such this optimisation is only used when using PostgreSQL 9.3 or
newer.

1 files changed, 4 insertions, 0 deletions

diff --git a/lib/gitlab/database.rb b/lib/gitlab/database.rb
index d7dab584a44..e001d25e7b7 100644
--- a/lib/gitlab/database.rb
+++ b/lib/gitlab/database.rb
@@ -25,6 +25,10 @@ module Gitlab
       database_version.match(/\A(?:PostgreSQL |)([^\s]+).*\z/)[1]
     end
 
+    def self.join_lateral_supported?
+      postgresql? && version.to_f >= 9.3
+    end
+
     def self.nulls_last_order(field, direction = 'ASC')
       order = "#{field} #{direction}"