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Alan Guo Xiang Tan 2f5e66b6f8
PERF: Optimise TopicTrackingState.report query to speed up query (#22871) 
In the query generated by `TopicTrackingState.report`, there are two
subqueies being executed. The first subquery fetches all the topics
that are new for a given user while the second subquery fetches all the topics with
unread posts for a given user. For the second subquery, there is a
filter `topics.updated_at >= user_stats.first_unread_at` which is used
as a performance optimisation to reduce the number of rows that PG has
to scan through the `topics` table.

However, we started to notice in production that the PG planner doesn't
always execute the filter first to reduce the number of rows that it has
to scan through. Running the following query in one of our production
instance,

```
EXPLAIN ANALYZE
SELECT
           DISTINCT topics.id as topic_id,
           u.id as user_id,
           topics.created_at,
           topics.updated_at,
           topics.highest_staff_post_number AS highest_post_number,
           last_read_post_number,
           c.id as category_id,
           c.topic_id AS category_topic_id,
           tu.notification_level,
           us.first_unread_at,
           GREATEST(
              CASE
              WHEN COALESCE(uo.new_topic_duration_minutes, 2880) = -1 THEN u.created_at
              WHEN COALESCE(uo.new_topic_duration_minutes, 2880) = -2 THEN COALESCE(
                u.previous_visit_at,u.created_at
              )
              ELSE ('2023-07-31 03:29:45.737630'::timestamp - INTERVAL '1 MINUTE' * COALESCE(uo.new_topic_duration_minutes, 2880))
              END, u.created_at, '2023-07-25 15:06:44'
           ) AS treat_as_new_topic_start_date
FROM topics
JOIN users u on u.id = 13455
JOIN user_stats AS us ON us.user_id = u.id
JOIN user_options AS uo ON uo.user_id = u.id
JOIN categories c ON c.id = topics.category_id
LEFT JOIN topic_users tu ON tu.topic_id = topics.id AND tu.user_id = u.id

WHERE u.id = 13455 AND
       topics.updated_at >= us.first_unread_at AND
      topics.archetype <> 'private_message' AND
      (("topics"."deleted_at" IS NULL AND (tu.last_read_post_number < topics.highest_staff_post_number) AND (COALESCE(tu.notification_level, 1) >= 2)) OR (1=0)) AND

      NOT (
  COALESCE((select array_agg(tag_id) from topic_tags where topic_tags.topic_id = topics.id), ARRAY[]::int[]) && ARRAY[451,452,453]
) AND

      topics.deleted_at IS NULL AND

      NOT (
        last_read_post_number IS NULL AND
        (
          topics.category_id IN (SELECT "categories"."id" FROM "categories" LEFT JOIN categories categories2 ON categories2.id = categories.parent_category_id LEFT JOIN category_users ON category_users.category_id = categories.id AND category_users.user_id = 13455 LEFT JOIN category_users category_users2 ON category_users2.category_id = categories2.id AND category_users2.user_id = 13455 WHERE ((category_users.id IS NULL AND COALESCE(category_users2.notification_level, 1) = 0) OR COALESCE(category_users.notification_level, 1) = 0))
          AND tu.notification_level <= 1
        )
      )
```

we get the following

```
                                                                                                                                                                                                                                                                                                                          QUERY PLAN
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 Unique  (cost=201606.06..201608.15 rows=76 width=60) (actual time=91.279..91.294 rows=14 loops=1)
   ->  Sort  (cost=201606.06..201606.25 rows=76 width=60) (actual time=91.278..91.284 rows=14 loops=1)
         Sort Key: topics.id, topics.created_at, topics.updated_at, topics.highest_staff_post_number, tu.last_read_post_number, c.id, c.topic_id, tu.notification_level, us.first_unread_at, (GREATEST(CASE WHEN (COALESCE(uo.new_topic_duration_minutes, 2880) = '-1'::integer) THEN u.created_at WHEN (COALESCE(uo.new_topic_duration_minutes, 2880) = '-2'::integer) THEN COALESCE(u.previous_visit_at, u.created_at) ELSE ('2023-07-31 03:29:45.73763'::timestamp without time zone - ('00:01:00'::interval * (COALESCE(uo.new_topic_duration_minutes, 2880))::double precision)) END, u.created_at, '2023-07-25 15:06:44'::timestamp without time zone))
         Sort Method: quicksort  Memory: 26kB
         ->  Hash Join  (cost=97519.51..201603.69 rows=76 width=60) (actual time=87.662..91.268 rows=14 loops=1)
               Hash Cond: (topics.id = tu.topic_id)
               Join Filter: ((tu.last_read_post_number < topics.highest_staff_post_number) AND ((tu.last_read_post_number IS NOT NULL) OR (NOT (hashed SubPlan 2)) OR (tu.notification_level > 1)))
               Rows Removed by Join Filter: 10
               ->  Nested Loop  (cost=1.54..104075.36 rows=3511 width=68) (actual time=0.055..3.609 rows=548 loops=1)
                     ->  Nested Loop  (cost=1.13..25.20 rows=1 width=32) (actual time=0.027..0.033 rows=1 loops=1)
                           ->  Nested Loop  (cost=0.71..16.76 rows=1 width=28) (actual time=0.020..0.023 rows=1 loops=1)
                                 ->  Index Scan using users_pkey on users u  (cost=0.42..8.44 rows=1 width=20) (actual time=0.010..0.012 rows=1 loops=1)
                                       Index Cond: (id = 13455)
                                 ->  Index Scan using user_stats_pkey on user_stats us  (cost=0.29..8.31 rows=1 width=12) (actual time=0.008..0.010 rows=1 loops=1)
                                       Index Cond: (user_id = 13455)
                           ->  Index Scan using index_user_options_on_user_id_and_default_calendar on user_options uo  (cost=0.42..8.44 rows=1 width=8) (actual time=0.007..0.008 rows=1 loops=1)
                                 Index Cond: (user_id = 13455)
                     ->  Nested Loop  (cost=0.41..104015.12 rows=3504 width=36) (actual time=0.026..3.503 rows=548 loops=1)
                           ->  Seq Scan on categories c  (cost=0.00..13.73 rows=73 width=8) (actual time=0.003..0.039 rows=73 loops=1)
                           ->  Index Only Scan using index_topics_on_updated_at_public on topics  (cost=0.41..1424.20 rows=48 width=28) (actual time=0.012..0.046 rows=8 loops=73)
                                 Index Cond: ((updated_at >= us.first_unread_at) AND (category_id = c.id))
                                 Filter: (NOT (COALESCE((SubPlan 1), '{}'::integer[]) && '{451,452,453}'::integer[]))
                                 Heap Fetches: 553
                                 SubPlan 1
                                   ->  Aggregate  (cost=4.31..4.32 rows=1 width=32) (actual time=0.002..0.002 rows=1 loops=548)
                                         ->  Index Only Scan using index_topic_tags_on_topic_id_and_tag_id on topic_tags  (cost=0.29..4.31 rows=1 width=4) (actual time=0.002..0.002 rows=1 loops=548)
                                               Index Cond: (topic_id = topics.id)
                                               Heap Fetches: 178
               ->  Hash  (cost=97222.14..97222.14 rows=19914 width=16) (actual time=87.545..87.546 rows=42884 loops=1)
                     Buckets: 65536 (originally 32768)  Batches: 1 (originally 1)  Memory Usage: 2387kB
                     ->  Bitmap Heap Scan on topic_users tu  (cost=1217.47..97222.14 rows=19914 width=16) (actual time=14.419..78.286 rows=42884 loops=1)
                           Recheck Cond: (user_id = 13455)
                           Filter: (COALESCE(notification_level, 1) >= 2)
                           Rows Removed by Filter: 15839
                           Heap Blocks: exact=45285
                           ->  Bitmap Index Scan on index_topic_users_on_user_id_and_topic_id  (cost=0.00..1212.49 rows=59741 width=0) (actual time=6.448..6.448 rows=58723 loops=1)
                                 Index Cond: (user_id = 13455)
               SubPlan 2
                 ->  Nested Loop Left Join  (cost=0.74..46.90 rows=1 width=4) (never executed)
                       Join Filter: (category_users2.category_id = categories2.id)
                       Filter: (((category_users.id IS NULL) AND (COALESCE(category_users2.notification_level, 1) = 0)) OR (COALESCE(category_users.notification_level, 1) = 0))
                       ->  Nested Loop Left Join  (cost=0.45..32.31 rows=73 width=16) (never executed)
                             Join Filter: (category_users.category_id = categories.id)
                             ->  Nested Loop Left Join  (cost=0.15..18.45 rows=73 width=8) (never executed)
                                   ->  Seq Scan on categories  (cost=0.00..13.73 rows=73 width=8) (never executed)
                                   ->  Memoize  (cost=0.15..0.28 rows=1 width=4) (never executed)
                                         Cache Key: categories.parent_category_id
                                         Cache Mode: logical
                                         ->  Index Only Scan using categories_pkey on categories categories2  (cost=0.14..0.27 rows=1 width=4) (never executed)
                                               Index Cond: (id = categories.parent_category_id)
                                               Heap Fetches: 0
                             ->  Materialize  (cost=0.29..11.69 rows=2 width=12) (never executed)
                                   ->  Index Scan using idx_category_users_user_id_category_id on category_users  (cost=0.29..11.68 rows=2 width=12) (never executed)
                                         Index Cond: (user_id = 13455)
                       ->  Materialize  (cost=0.29..11.69 rows=2 width=8) (never executed)
                             ->  Index Scan using idx_category_users_user_id_category_id on category_users category_users2  (cost=0.29..11.68 rows=2 width=8) (never executed)
                                   Index Cond: (user_id = 13455)
 Planning Time: 1.740 ms
 Execution Time: 91.414 ms
(59 rows)
```

From the execution plan, we can see the most of the time is spent
joining about 42888 rows in the `topics` table to the `topic_users` table.
However, we know that we only have to scan through a
subset of the `topics` table because the user's last unread at is '2023-07-20 11:33:05'.
If we filter the `topics` table with `topics.updated_at >= '2023-07-20 11:33:05'`, this would only
return about 1500 rows.

From our testing in production, the PG planner is able to execute a
better query plan when we avoid the unnecessary joins on `user_stats` just to be
able to get the user's `UserStat#first_unread_at`. Instead, we can just
pass the value of `UserStat#first_unread_at` directly as a query
parameter.

```
EXPLAIN ANALYZE
SELECT
           DISTINCT topics.id as topic_id,
           u.id as user_id,
           topics.created_at,
           topics.updated_at,
           topics.highest_staff_post_number AS highest_post_number,
           last_read_post_number,
           c.id as category_id,
           c.topic_id AS category_topic_id,
           tu.notification_level,
           GREATEST(
              CASE
              WHEN COALESCE(uo.new_topic_duration_minutes, 2880) = -1 THEN u.created_at
              WHEN COALESCE(uo.new_topic_duration_minutes, 2880) = -2 THEN COALESCE(
                u.previous_visit_at,u.created_at
              )
              ELSE ('2023-07-31 03:29:45.737630'::timestamp - INTERVAL '1 MINUTE' * COALESCE(uo.new_topic_duration_minutes, 2880))
              END, u.created_at, '2023-07-25 15:06:44'
           ) AS treat_as_new_topic_start_date
FROM topics
JOIN users u on u.id = 13455
JOIN user_options AS uo ON uo.user_id = u.id
JOIN categories c ON c.id = topics.category_id
LEFT JOIN topic_users tu ON tu.topic_id = topics.id AND tu.user_id = u.id

WHERE u.id = 13455 AND
       topics.updated_at >= '2023-07-20 11:33:05' AND
      topics.archetype <> 'private_message' AND
      (("topics"."deleted_at" IS NULL AND (tu.last_read_post_number < topics.highest_staff_post_number) AND (COALESCE(tu.notification_level, 1) >= 2)) OR (1=0)) AND

      NOT (
  COALESCE((select array_agg(tag_id) from topic_tags where topic_tags.topic_id = topics.id), ARRAY[]::int[]) && ARRAY[451,452,453]
) AND

      topics.deleted_at IS NULL AND

      NOT (
        last_read_post_number IS NULL AND
        (
          topics.category_id IN (SELECT "categories"."id" FROM "categories" LEFT JOIN categories categories2 ON categories2.id = categories.parent_category_id LEFT JOIN category_users ON category_users.category_id = categories.id AND category_users.user_id = 13455 LEFT JOIN category_users category_users2 ON category_users2.category_id = categories2.id AND category_users2.user_id = 13455 WHERE ((category_users.id IS NULL AND COALESCE(category_users2.notification_level, 1) = 0) OR COALESCE(category_users.notification_level, 1) = 0))
          AND tu.notification_level <= 1
        )
      );
```

Note how the filter is now `topics.updated_at >= '2023-07-20 11:33:05'`
instead of `topics.updated_at >= us.first_unread_at`. The modified query
above generates the following execution plan.

```
                                                                                                                                                                                                                                                                                                                QUERY PLAN
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 Unique  (cost=5189.86..5189.88 rows=1 width=52) (actual time=4.991..5.002 rows=14 loops=1)
   ->  Sort  (cost=5189.86..5189.86 rows=1 width=52) (actual time=4.990..4.994 rows=14 loops=1)
         Sort Key: topics.id, topics.created_at, topics.updated_at, topics.highest_staff_post_number, tu.last_read_post_number, c.id, c.topic_id, tu.notification_level, (GREATEST(CASE WHEN (COALESCE(uo.new_topic_duration_minutes, 2880) = '-1'::integer) THEN u.created_at WHEN (COALESCE(uo.new_topic_duration_minutes, 2880) = '-2'::integer) THEN COALESCE(u.previous_visit_at, u.created_at) ELSE ('2023-07-31 03:29:45.73763'::timestamp without time zone - ('00:01:00'::interval * (COALESCE(uo.new_topic_duration_minutes, 2880))::double precision)) END, u.created_at, '2023-07-25 15:06:44'::timestamp without time zone))
         Sort Method: quicksort  Memory: 26kB
         ->  Nested Loop  (cost=52.11..5189.85 rows=1 width=52) (actual time=0.093..4.974 rows=14 loops=1)
               ->  Nested Loop  (cost=51.70..5181.39 rows=1 width=60) (actual time=0.084..4.931 rows=14 loops=1)
                     ->  Nested Loop  (cost=51.28..5172.94 rows=1 width=44) (actual time=0.076..4.887 rows=14 loops=1)
                           ->  Nested Loop  (cost=0.41..1698.46 rows=59 width=36) (actual time=0.029..3.537 rows=548 loops=1)
                                 ->  Seq Scan on categories c  (cost=0.00..13.73 rows=73 width=8) (actual time=0.005..0.039 rows=73 loops=1)
                                 ->  Index Only Scan using index_topics_on_updated_at_public on topics  (cost=0.41..23.07 rows=1 width=28) (actual time=0.012..0.047 rows=8 loops=73)
                                       Index Cond: ((updated_at >= '2023-07-20 11:33:05'::timestamp without time zone) AND (category_id = c.id))
                                       Filter: (NOT (COALESCE((SubPlan 1), '{}'::integer[]) && '{451,452,453}'::integer[]))
                                       Heap Fetches: 552
                                       SubPlan 1
                                         ->  Aggregate  (cost=4.31..4.32 rows=1 width=32) (actual time=0.002..0.002 rows=1 loops=548)
                                               ->  Index Only Scan using index_topic_tags_on_topic_id_and_tag_id on topic_tags  (cost=0.29..4.31 rows=1 width=4) (actual time=0.002..0.002 rows=1 loops=548)
                                                     Index Cond: (topic_id = topics.id)
                                                     Heap Fetches: 178
                           ->  Index Scan using index_topic_users_on_user_id_and_topic_id on topic_users tu  (cost=50.86..58.88 rows=1 width=16) (actual time=0.002..0.002 rows=0 loops=548)
                                 Index Cond: ((user_id = 13455) AND (topic_id = topics.id))
                                 Filter: ((COALESCE(notification_level, 1) >= 2) AND (last_read_post_number < topics.highest_staff_post_number) AND ((last_read_post_number IS NOT NULL) OR (NOT (hashed SubPlan 2)) OR (notification_level > 1)))
                                 Rows Removed by Filter: 0
                                 SubPlan 2
                                   ->  Nested Loop Left Join  (cost=0.74..50.43 rows=1 width=4) (never executed)
                                         Join Filter: (category_users2.category_id = categories2.id)
                                         Filter: (((category_users.id IS NULL) AND (COALESCE(category_users2.notification_level, 1) = 0)) OR (COALESCE(category_users.notification_level, 1) = 0))
                                         ->  Nested Loop Left Join  (cost=0.45..35.84 rows=73 width=16) (never executed)
                                               Join Filter: (category_users.category_id = categories.id)
                                               ->  Nested Loop Left Join  (cost=0.15..21.97 rows=73 width=8) (never executed)
                                                     ->  Seq Scan on categories  (cost=0.00..13.73 rows=73 width=8) (never executed)
                                                     ->  Memoize  (cost=0.15..0.61 rows=1 width=4) (never executed)
                                                           Cache Key: categories.parent_category_id
                                                           Cache Mode: logical
                                                           ->  Index Only Scan using categories_pkey on categories categories2  (cost=0.14..0.60 rows=1 width=4) (never executed)
                                                                 Index Cond: (id = categories.parent_category_id)
                                                                 Heap Fetches: 0
                                               ->  Materialize  (cost=0.29..11.69 rows=2 width=12) (never executed)
                                                     ->  Index Scan using idx_category_users_user_id_category_id on category_users  (cost=0.29..11.68 rows=2 width=12) (never executed)
                                                           Index Cond: (user_id = 13455)
                                         ->  Materialize  (cost=0.29..11.69 rows=2 width=8) (never executed)
                                               ->  Index Scan using idx_category_users_user_id_category_id on category_users category_users2  (cost=0.29..11.68 rows=2 width=8) (never executed)
                                                     Index Cond: (user_id = 13455)
                     ->  Index Scan using users_pkey on users u  (cost=0.42..8.44 rows=1 width=20) (actual time=0.003..0.003 rows=1 loops=14)
                           Index Cond: (id = 13455)
               ->  Index Scan using index_user_options_on_user_id_and_default_calendar on user_options uo  (cost=0.42..8.44 rows=1 width=8) (actual time=0.002..0.002 rows=1 loops=14)
                     Index Cond: (user_id = 13455)
 Planning Time: 1.281 ms
 Execution Time: 5.092 ms
(48 rows)
```

With the new query, PG first does an index scan using the `index_topics_on_updated_at_public` index to filter away most of the topics making the subsequent joins much cheaper. Total query time has been reduced from ~90ms to ~5ms.

This optimisation will mostly affect users with very few/recent unread topics since a large `UserStat#firsts_unread_at` value will still mean scanning through a large portion of the `topics` table.
2023-07-31 12:21:41 +08:00
.devcontainer DEV: Replace postCreateCommand with postStartCommand (#16665) 2022-05-05 23:52:35 +02:00
.github FIX: specify chrome version (#22681) 2023-07-19 15:06:56 +10:00
.vscode-sample DEV: introduce Ember <template> tag support (.gjs) (#22719) 2023-07-20 21:01:12 +01:00
app PERF: Optimise TopicTrackingState.report query to speed up query (#22871) 2023-07-31 12:21:41 +08:00
bin DEV: Use runtime info to split test files for parallel testing (#22060) 2023-06-12 09:07:17 +08:00
config SECURITY: Don't reuse CSP nonce between anonymous requests 2023-07-28 12:53:44 +01:00
db DEV: Delete upload references upon deleting draft (#22851) 2023-07-31 10:16:23 +08:00
docs Update ADMIN-QUICK-START-GUIDE.md (#22788) 2023-07-27 08:44:38 -07:00
documentation DEV: Fix random typos (#20937) 2023-04-03 19:27:32 +02:00
images
lib DEV: Update code comment wording (#22861) 2023-07-28 11:47:22 -06:00
log
plugins FIX: Chat translation minor issues (#22869) 2023-07-31 11:44:32 +10:00
public DEV: Update diffhtml to 1.0.0-beta.29 again (#22365) 2023-07-03 19:38:43 +03:00
script FIX: user_id arg override in Slack import (#22713) 2023-07-20 11:22:43 +00:00
spec FIX: Can't dismiss unread posts in topics of a sub-subcategory (#22870) 2023-07-31 11:22:16 +08:00
test DEV: Run tests with new chrome headless (#21684) 2023-05-26 11:02:56 +02:00
vendor DEV: Update moment-timezone-with-data (#22313) 2023-06-28 11:33:55 +02:00
.editorconfig DEV: Update .editorconfig to match new hbs rules (#19816) 2023-01-10 16:21:16 +01:00
.eslintignore DEV: Chat service object initial implementation (#19814) 2023-02-13 13:09:57 +01:00
.eslintrc DEV: Await for all async MessageBus callbacks (#17966) 2022-08-17 12:44:48 +02:00
.git-blame-ignore-revs DEV: Add recent formatting commits to .git-blame-ignore-revs (#19799) 2023-01-09 14:51:48 +00:00
.gitattributes DEV: introduce Ember <template> tag support (.gjs) (#22719) 2023-07-20 21:01:12 +01:00
.gitignore DEV: introduce Ember <template> tag support (.gjs) (#22719) 2023-07-20 21:01:12 +01:00
.jsdoc DEV: Chat service object initial implementation (#19814) 2023-02-13 13:09:57 +01:00
.licensed.yml Build(deps): Bump nio4r from 2.5.8 to 2.5.9 (#20947) 2023-04-04 02:28:29 +02:00
.licensee.json DEV: Update eslint/prettier (#22226) 2023-06-21 20:59:03 +02:00
.npmrc
.prettierignore DEV: Chat service object initial implementation (#19814) 2023-02-13 13:09:57 +01:00
.prettierrc DEV: introduce Ember <template> tag support (.gjs) (#22719) 2023-07-20 21:01:12 +01:00
.rspec Add RSpec 4 compatibility (#17652) 2022-07-28 10:27:38 +08:00
.rspec_parallel
.rubocop.yml DEV: Enable unless cops 2023-02-21 10:30:48 +01:00
.ruby-gemset.sample
.ruby-version.sample DEV: Update recommended Ruby to 3.2.1 (#20444) 2023-02-24 12:51:34 -03:00
.streerc DEV: Apply syntax_tree formatting to app/* 2023-01-09 14:14:59 +00:00
.template-lintrc.js DEV: Fix no-negated-condition linting issues (#22808) 2023-07-26 19:53:37 +02:00
Brewfile
config.ru
CONTRIBUTING.md
COPYRIGHT.md
d
discourse.sublime-project
Gemfile DEV: moves logic from job to a service (#22691) 2023-07-27 10:25:41 +02:00
Gemfile.lock Build(deps): Bump zeitwerk from 2.6.9 to 2.6.10 (#22866) 2023-07-31 09:18:21 +08:00
jsconfig.base.json DEV: introduce Ember <template> tag support (.gjs) (#22719) 2023-07-20 21:01:12 +01:00
lefthook.yml DEV: Add syntax_tree check to lefthook (#19877) 2023-01-17 10:16:07 +10:00
LICENSE.txt
package.json DEV: introduce Ember <template> tag support (.gjs) (#22719) 2023-07-20 21:01:12 +01:00
Rakefile
README.md DEV: Update recommended Ruby to 3.2.1 (#20444) 2023-02-24 12:51:34 -03:00
translator.yml DEV: Add labels for plugin locale files (#19664) 2022-12-31 00:37:15 +01:00
yarn.lock DEV: introduce Ember <template> tag support (.gjs) (#22719) 2023-07-20 21:01:12 +01:00

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  • Ember.js — Our front end is an Ember.js app that communicates with the Rails API.
  • PostgreSQL — Our main data store is in Postgres.
  • Redis — We use Redis as a cache and for transient data.
  • BrowserStack — We use BrowserStack to test on real devices and browsers.

Plus lots of Ruby Gems, a complete list of which is at /main/Gemfile.

Contributing

Build Status

Discourse is 100% free and open source. We encourage and support an active, healthy community that
accepts contributions from the public – including you!

Before contributing to Discourse:

  1. Please read the complete mission statements on discourse.org. Yes we actually believe this stuff; you should too.
  2. Read and sign the Electronic Discourse Forums Contribution License Agreement.
  3. Dig into CONTRIBUTING.MD, which covers submitting bugs, requesting new features, preparing your code for a pull request, etc.
  4. Always strive to collaborate with mutual respect.
  5. Not sure what to work on? We've got some ideas.

We look forward to seeing your pull requests!

Security

We take security very seriously at Discourse; all our code is 100% open source and peer reviewed. Please read our security guide for an overview of security measures in Discourse, or if you wish to report a security issue.

The Discourse Team

The original Discourse code contributors can be found in AUTHORS.MD. For a complete list of the many individuals that contributed to the design and implementation of Discourse, please refer to the official Discourse blog and GitHub's list of contributors.

Copyright / License

Copyright 2014 - 2023 Civilized Discourse Construction Kit, Inc.

Licensed under the GNU General Public License Version 2.0 (or later);
you may not use this work except in compliance with the License.
You may obtain a copy of the License in the LICENSE file, or at:

https://www.gnu.org/licenses/old-licenses/gpl-2.0.txt

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.

Discourse logo and “Discourse Forum” ®, Civilized Discourse Construction Kit, Inc.

Accessibility

To guide our ongoing effort to build accessible software we follow the W3C’s Web Content Accessibility Guidelines (WCAG). If you'd like to report an accessibility issue that makes it difficult for you to use Discourse, email accessibility@discourse.org. For more information visit discourse.org/accessibility.

Dedication

Discourse is built with love, Internet style.