This new setup no longer loads any IDs into memory using "pluck",
instead using SQL UNIONs to merge the various datasets together. This
results in greatly improved query performance as well as a reduction of
memory usage.

The old setup was in particular problematic when requesting the
authorized projects _including_ public/internal projects as this would
result in roughly 65000 project IDs being loaded into memory. These IDs
would in turn be passed to other queries.

This removes the need for plucking any IDs into Ruby.

By moving the default sort order into a separate scope (and calling this
from the default scope) we can more easily re-apply a default order
without having to specify the exact column/ordering all over the place.

This allows retrieving of the list of authorized projects using a single
query, without having to load any IDs into Ruby. This in turn also means
we can remove the method User#authorized_projects_id.

This class can be used to join multiple AcitveRecord::Relation objects
together using a SQL UNION statement. ActiveRecord < 5.0 sadly doesn't
support UNION and existing Gems out there don't handle prepared
statements (e.g. they never incremented the variable bindings).

Instead of using MAX(events.updated_at) we can simply sort the events in
descending order by the "id" column and grab the first row. In other
words, instead of this:

    SELECT max(events.updated_at) AS max_id
    FROM events
    LEFT OUTER JOIN projects   ON projects.id   = events.project_id
    LEFT OUTER JOIN namespaces ON namespaces.id = projects.namespace_id
    WHERE events.author_id IS NOT NULL
    AND events.project_id IN (13083);

we can use this:

    SELECT events.updated_at AS max_id
    FROM events
    LEFT OUTER JOIN projects   ON projects.id   = events.project_id
    LEFT OUTER JOIN namespaces ON namespaces.id = projects.namespace_id
    WHERE events.author_id IS NOT NULL
    AND events.project_id IN (13083)
    ORDER BY events.id DESC
    LIMIT 1;

This has the benefit that on PostgreSQL a backwards index scan can be
used, which due to the "LIMIT 1" will at most process only a single row.
This in turn greatly speeds up the process of grabbing the latest update
time. This can be confirmed by looking at the query plans. The first
query produces the following plan:

    Aggregate  (cost=43779.84..43779.85 rows=1 width=12) (actual time=2142.462..2142.462 rows=1 loops=1)
      ->  Index Scan using index_events_on_project_id on events  (cost=0.43..43704.69 rows=30060 width=12) (actual time=0.033..2138.086 rows=32769 loops=1)
            Index Cond: (project_id = 13083)
            Filter: (author_id IS NOT NULL)
    Planning time: 1.248 ms
    Execution time: 2142.548 ms

The second query in turn produces the following plan:

    Limit  (cost=0.43..41.65 rows=1 width=16) (actual time=1.394..1.394 rows=1 loops=1)
      ->  Index Scan Backward using events_pkey on events  (cost=0.43..1238907.96 rows=30060 width=16) (actual time=1.394..1.394 rows=1 loops=1)
            Filter: ((author_id IS NOT NULL) AND (project_id = 13083))
            Rows Removed by Filter: 2104
    Planning time: 0.166 ms
    Execution time: 1.408 ms

According to the above plans the 2nd query is around 1500 times faster.
However, re-running the first query produces timings of around 80 ms,
making the 2nd query "only" around 55 times faster.

Documentation for Git LFS

Doc explaining how to use Git LFS, how to use Git LFS with GitLab, known issues and troubleshooting tips.

See merge request !1813

More labels since we get more specializations.

/cc @creamzy @ernstvn @dzaporozhets 

See merge request !1821

Correctly set comparison first commit when range includes a merge commit

Fixes #3207.

See merge request !1814

[ci skip]

See merge request !1705

Add notification to the former assignee upon unassignment

Replaces !1769

Fixes #3395

See merge request !1818

Prevent the last owner of a group from being able to delete themselves
by 'adding' themselves as a master

Replaces !1708.

Fixes #1111.

See merge request !1815

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

[ci skip]

See merge request !1816

[ci skip]

[ci skip]

Don't render note edit forms for visitors

Reverted #9820, github/task_list need a form, textarea for update.

Revert "Merge pull request #9820 from huacnlee/avoid-render-form-in-notes-list"

This reverts commit 63144cd0, reversing
changes made to 8ab5df9d.

Reverts https://github.com/gitlabhq/gitlabhq/pull/9820

See merge request !1804