What is the context of this change?
Before 7c6a8f1c74, we were using
`preload(:tags)` on the topics relation but that was accidentally
removed in the refactor. This was discovered and fixed in
5bec894a8c but insteadl of using
`preload(:tags)` we ended up using `includes(:tags)`. The problem here
is that `includes(:tags)` can either result in `preload(:tags)` or
`eager_load(:tags)` but for some reason ActiveRecord is deciding to
`eager_load(:tags)` resulting in a joins to the `topic_tags` and `tags`
table which is not necessarily and leads to more inefficient queries.
When `includes(:tags)` is used, listing the latest topics ended up
generating the following sample queries to fetch the list of topics to display.
```
SELECT DISTINCT "topics"."pinned_at" AS alias_0, "topics"."id" FROM "topics" LEFT OUTER JOIN "categories" ON "categories"."id" = "topics"."category_id" LEFT OUTER JOIN "topic_tags" ON "topic_tags"."topic_id" = "topics"."id" LEFT OUTER JOIN "tags" ON "tags"."id" = "topic_tags"."tag_id" LEFT OUTER JOIN topic_users AS tu ON (topics.id = tu.topic_id AND tu.user_id = 29) LEFT JOIN category_users ON category_users.category_id = topics.category_id AND category_users.user_id = 29 WHERE "topics"."deleted_at" IS NULL AND (topics.archetype <> 'private_message') AND (COALESCE(categories.topic_id, 0) <> topics.id) AND (COALESCE(tu.notification_level,1) > 0) AND (topics.category_id = -1
OR
(COALESCE(category_users.notification_level, 1) <> 0 AND (topics.category_id IS NULL OR topics.category_id NOT IN(-1)))
OR tu.notification_level > 1) AND (pinned_globally AND pinned_at IS NOT NULL AND (topics.pinned_at > tu.cleared_pinned_at OR tu.cleared_pinned_at IS NULL)) ORDER BY "topics"."pinned_at" DESC LIMIT 30
SELECT "topics"."id" AS t0_r0, "topics"."title" AS t0_r1, "topics"."last_posted_at" AS t0_r2, "topics"."created_at" AS t0_r3, "topics"."updated_at" AS t0_r4, "topics"."views" AS t0_r5, "topics"."posts_count" AS t0_r6, "topics"."user_id" AS t0_r7, "topics"."last_post_user_id" AS t0_r8, "topics"."reply_count" AS t0_r9, "topics"."featured_user1_id" AS t0_r10, "topics"."featured_user2_id" AS t0_r11, "topics"."featured_user3_id" AS t0_r12, "topics"."deleted_at" AS t0_r13, "topics"."highest_post_number" AS t0_r14, "topics"."like_count" AS t0_r15, "topics"."incoming_link_count" AS t0_r16, "topics"."category_id" AS t0_r17, "topics"."visible" AS t0_r18, "topics"."moderator_posts_count" AS t0_r19, "topics"."closed" AS t0_r20, "topics"."archived" AS t0_r21, "topics"."bumped_at" AS t0_r22, "topics"."has_summary" AS t0_r23, "topics"."archetype" AS t0_r24, "topics"."featured_user4_id" AS t0_r25, "topics"."notify_moderators_count" AS t0_r26, "topics"."spam_count" AS t0_r27, "topics"."pinned_at" AS t0_r28, "topics"."score" AS t0_r29, "topics"."percent_rank" AS t0_r30, "topics"."subtype" AS t0_r31, "topics"."slug" AS t0_r32, "topics"."deleted_by_id" AS t0_r33, "topics"."participant_count" AS t0_r34, "topics"."word_count" AS t0_r35, "topics"."excerpt" AS t0_r36, "topics"."pinned_globally" AS t0_r37, "topics"."pinned_until" AS t0_r38, "topics"."fancy_title" AS t0_r39, "topics"."highest_staff_post_number" AS t0_r40, "topics"."featured_link" AS t0_r41, "topics"."reviewable_score" AS t0_r42, "topics"."image_upload_id" AS t0_r43, "topics"."slow_mode_seconds" AS t0_r44, "topics"."bannered_until" AS t0_r45, "topics"."external_id" AS t0_r46, "categories"."id" AS t1_r0, "categories"."name" AS t1_r1, "categories"."color" AS t1_r2, "categories"."topic_id" AS t1_r3, "categories"."topic_count" AS t1_r4, "categories"."created_at" AS t1_r5, "categories"."updated_at" AS t1_r6, "categories"."user_id" AS t1_r7, "categories"."topics_year" AS t1_r8, "categories"."topics_month" AS t1_r9, "categories"."topics_week" AS t1_r10, "categories"."slug" AS t1_r11, "categories"."description" AS t1_r12, "categories"."text_color" AS t1_r13, "categories"."read_restricted" AS t1_r14, "categories"."auto_close_hours" AS t1_r15, "categories"."post_count" AS t1_r16, "categories"."latest_post_id" AS t1_r17, "categories"."latest_topic_id" AS t1_r18, "categories"."position" AS t1_r19, "categories"."parent_category_id" AS t1_r20, "categories"."posts_year" AS t1_r21, "categories"."posts_month" AS t1_r22, "categories"."posts_week" AS t1_r23, "categories"."email_in" AS t1_r24, "categories"."email_in_allow_strangers" AS t1_r25, "categories"."topics_day" AS t1_r26, "categories"."posts_day" AS t1_r27, "categories"."allow_badges" AS t1_r28, "categories"."name_lower" AS t1_r29, "categories"."auto_close_based_on_last_post" AS t1_r30, "categories"."topic_template" AS t1_r31, "categories"."contains_messages" AS t1_r32, "categories"."sort_order" AS t1_r33, "categories"."sort_ascending" AS t1_r34, "categories"."uploaded_logo_id" AS t1_r35, "categories"."uploaded_background_id" AS t1_r36, "categories"."topic_featured_link_allowed" AS t1_r37, "categories"."all_topics_wiki" AS t1_r38, "categories"."show_subcategory_list" AS t1_r39, "categories"."num_featured_topics" AS t1_r40, "categories"."default_view" AS t1_r41, "categories"."subcategory_list_style" AS t1_r42, "categories"."default_top_period" AS t1_r43, "categories"."mailinglist_mirror" AS t1_r44, "categories"."minimum_required_tags" AS t1_r45, "categories"."navigate_to_first_post_after_read" AS t1_r46, "categories"."search_priority" AS t1_r47, "categories"."allow_global_tags" AS t1_r48, "categories"."reviewable_by_group_id" AS t1_r49, "categories"."read_only_banner" AS t1_r50, "categories"."default_list_filter" AS t1_r51, "categories"."allow_unlimited_owner_edits_on_first_post" AS t1_r52, "categories"."default_slow_mode_seconds" AS t1_r53, "categories"."uploaded_logo_dark_id" AS t1_r54, "tags"."id" AS t2_r0, "tags"."name" AS t2_r1, "tags"."created_at" AS t2_r2, "tags"."updated_at" AS t2_r3, "tags"."pm_topic_count" AS t2_r4, "tags"."target_tag_id" AS t2_r5, "tags"."description" AS t2_r6, "tags"."public_topic_count" AS t2_r7, "tags"."staff_topic_count" AS t2_r8 FROM "topics" LEFT OUTER JOIN "categories" ON "categories"."id" = "topics"."category_id" LEFT OUTER JOIN "topic_tags" ON "topic_tags"."topic_id" = "topics"."id" LEFT OUTER JOIN "tags" ON "tags"."id" = "topic_tags"."tag_id" LEFT OUTER JOIN topic_users AS tu ON (topics.id = tu.topic_id AND tu.user_id = 29) LEFT JOIN category_users ON category_users.category_id = topics.category_id AND category_users.user_id = 29 WHERE "topics"."deleted_at" IS NULL AND (topics.archetype <> 'private_message') AND (COALESCE(categories.topic_id, 0) <> topics.id) AND (COALESCE(tu.notification_level,1) > 0) AND (topics.category_id = -1
OR
(COALESCE(category_users.notification_level, 1) <> 0 AND (topics.category_id IS NULL OR topics.category_id NOT IN(-1)))
OR tu.notification_level > 1) AND (pinned_globally AND pinned_at IS NOT NULL AND (topics.pinned_at > tu.cleared_pinned_at OR tu.cleared_pinned_at IS NULL)) AND "topics"."id" = 7 ORDER BY "topics"."pinned_at" DESC
SELECT DISTINCT topics.bumped_at AS alias_0, "topics"."id" FROM "topics" LEFT OUTER JOIN "categories" ON "categories"."id" = "topics"."category_id" LEFT OUTER JOIN "topic_tags" ON "topic_tags"."topic_id" = "topics"."id" LEFT OUTER JOIN "tags" ON "tags"."id" = "topic_tags"."tag_id" LEFT OUTER JOIN topic_users AS tu ON (topics.id = tu.topic_id AND tu.user_id = 29) LEFT JOIN category_users ON category_users.category_id = topics.category_id AND category_users.user_id = 29 WHERE "topics"."deleted_at" IS NULL AND (topics.archetype <> 'private_message') AND (COALESCE(categories.topic_id, 0) <> topics.id) AND (COALESCE(tu.notification_level,1) > 0) AND (topics.category_id = -1
OR
(COALESCE(category_users.notification_level, 1) <> 0 AND (topics.category_id IS NULL OR topics.category_id NOT IN(-1)))
OR tu.notification_level > 1) AND (NOT ( pinned_globally AND pinned_at IS NOT NULL AND (topics.pinned_at > tu.cleared_pinned_at OR tu.cleared_pinned_at IS NULL) )) ORDER BY topics.bumped_at DESC LIMIT 30
SELECT "topics"."id" AS t0_r0, "topics"."title" AS t0_r1, "topics"."last_posted_at" AS t0_r2, "topics"."created_at" AS t0_r3, "topics"."updated_at" AS t0_r4, "topics"."views" AS t0_r5, "topics"."posts_count" AS t0_r6, "topics"."user_id" AS t0_r7, "topics"."last_post_user_id" AS t0_r8, "topics"."reply_count" AS t0_r9, "topics"."featured_user1_id" AS t0_r10, "topics"."featured_user2_id" AS t0_r11, "topics"."featured_user3_id" AS t0_r12, "topics"."deleted_at" AS t0_r13, "topics"."highest_post_number" AS t0_r14, "topics"."like_count" AS t0_r15, "topics"."incoming_link_count" AS t0_r16, "topics"."category_id" AS t0_r17, "topics"."visible" AS t0_r18, "topics"."moderator_posts_count" AS t0_r19, "topics"."closed" AS t0_r20, "topics"."archived" AS t0_r21, "topics"."bumped_at" AS t0_r22, "topics"."has_summary" AS t0_r23, "topics"."archetype" AS t0_r24, "topics"."featured_user4_id" AS t0_r25, "topics"."notify_moderators_count" AS t0_r26, "topics"."spam_count" AS t0_r27, "topics"."pinned_at" AS t0_r28, "topics"."score" AS t0_r29, "topics"."percent_rank" AS t0_r30, "topics"."subtype" AS t0_r31, "topics"."slug" AS t0_r32, "topics"."deleted_by_id" AS t0_r33, "topics"."participant_count" AS t0_r34, "topics"."word_count" AS t0_r35, "topics"."excerpt" AS t0_r36, "topics"."pinned_globally" AS t0_r37, "topics"."pinned_until" AS t0_r38, "topics"."fancy_title" AS t0_r39, "topics"."highest_staff_post_number" AS t0_r40, "topics"."featured_link" AS t0_r41, "topics"."reviewable_score" AS t0_r42, "topics"."image_upload_id" AS t0_r43, "topics"."slow_mode_seconds" AS t0_r44, "topics"."bannered_until" AS t0_r45, "topics"."external_id" AS t0_r46, "categories"."id" AS t1_r0, "categories"."name" AS t1_r1, "categories"."color" AS t1_r2, "categories"."topic_id" AS t1_r3, "categories"."topic_count" AS t1_r4, "categories"."created_at" AS t1_r5, "categories"."updated_at" AS t1_r6, "categories"."user_id" AS t1_r7, "categories"."topics_year" AS t1_r8, "categories"."topics_month" AS t1_r9, "categories"."topics_week" AS t1_r10, "categories"."slug" AS t1_r11, "categories"."description" AS t1_r12, "categories"."text_color" AS t1_r13, "categories"."read_restricted" AS t1_r14, "categories"."auto_close_hours" AS t1_r15, "categories"."post_count" AS t1_r16, "categories"."latest_post_id" AS t1_r17, "categories"."latest_topic_id" AS t1_r18, "categories"."position" AS t1_r19, "categories"."parent_category_id" AS t1_r20, "categories"."posts_year" AS t1_r21, "categories"."posts_month" AS t1_r22, "categories"."posts_week" AS t1_r23, "categories"."email_in" AS t1_r24, "categories"."email_in_allow_strangers" AS t1_r25, "categories"."topics_day" AS t1_r26, "categories"."posts_day" AS t1_r27, "categories"."allow_badges" AS t1_r28, "categories"."name_lower" AS t1_r29, "categories"."auto_close_based_on_last_post" AS t1_r30, "categories"."topic_template" AS t1_r31, "categories"."contains_messages" AS t1_r32, "categories"."sort_order" AS t1_r33, "categories"."sort_ascending" AS t1_r34, "categories"."uploaded_logo_id" AS t1_r35, "categories"."uploaded_background_id" AS t1_r36, "categories"."topic_featured_link_allowed" AS t1_r37, "categories"."all_topics_wiki" AS t1_r38, "categories"."show_subcategory_list" AS t1_r39, "categories"."num_featured_topics" AS t1_r40, "categories"."default_view" AS t1_r41, "categories"."subcategory_list_style" AS t1_r42, "categories"."default_top_period" AS t1_r43, "categories"."mailinglist_mirror" AS t1_r44, "categories"."minimum_required_tags" AS t1_r45, "categories"."navigate_to_first_post_after_read" AS t1_r46, "categories"."search_priority" AS t1_r47, "categories"."allow_global_tags" AS t1_r48, "categories"."reviewable_by_group_id" AS t1_r49, "categories"."read_only_banner" AS t1_r50, "categories"."default_list_filter" AS t1_r51, "categories"."allow_unlimited_owner_edits_on_first_post" AS t1_r52, "categories"."default_slow_mode_seconds" AS t1_r53, "categories"."uploaded_logo_dark_id" AS t1_r54, "tags"."id" AS t2_r0, "tags"."name" AS t2_r1, "tags"."created_at" AS t2_r2, "tags"."updated_at" AS t2_r3, "tags"."pm_topic_count" AS t2_r4, "tags"."target_tag_id" AS t2_r5, "tags"."description" AS t2_r6, "tags"."public_topic_count" AS t2_r7, "tags"."staff_topic_count" AS t2_r8 FROM "topics" LEFT OUTER JOIN "categories" ON "categories"."id" = "topics"."category_id" LEFT OUTER JOIN "topic_tags" ON "topic_tags"."topic_id" = "topics"."id" LEFT OUTER JOIN "tags" ON "tags"."id" = "topic_tags"."tag_id" LEFT OUTER JOIN topic_users AS tu ON (topics.id = tu.topic_id AND tu.user_id = 29) LEFT JOIN category_users ON category_users.category_id = topics.category_id AND category_users.user_id = 29 WHERE "topics"."deleted_at" IS NULL AND (topics.archetype <> 'private_message') AND (COALESCE(categories.topic_id, 0) <> topics.id) AND (COALESCE(tu.notification_level,1) > 0) AND (topics.category_id = -1
OR
(COALESCE(category_users.notification_level, 1) <> 0 AND (topics.category_id IS NULL OR topics.category_id NOT IN(-1)))
OR tu.notification_level > 1) AND (NOT ( pinned_globally AND pinned_at IS NOT NULL AND (topics.pinned_at > tu.cleared_pinned_at OR tu.cleared_pinned_at IS NULL) )) AND "topics"."id" IN (477, 481, 480, 479, 478, 467, 466, 230, 209, 183, 173, 179, 168, 139, 102, 144, 150, 118, 126, 88, 63, 46, 117, 171, 45, 77, 154, 158, 43, 79) ORDER BY topics.bumped_at DESC
```
Note how there are two extra queries which has to select `DISTINCT
topics.pinned_at` and `DISTINCT topics.bumped_at` because of the
unnecessary left joins to the `topic_tags` and `tags` table result in
duplicated rows in the topic tables. As a result, PG is not able to
use our indexes to effectively execute the query.
Comparing this to the queries being executed when `preload(:tags)` is
used.
```
SELECT "topics"."id" AS t0_r0, "topics"."title" AS t0_r1, "topics"."last_posted_at" AS t0_r2, "topics"."created_at" AS t0_r3, "topics"."updated_at" AS t0_r4, "topics"."views" AS t0_r5, "topics"."posts_count" AS t0_r6, "topics"."user_id" AS t0_r7, "topics"."last_post_user_id" AS t0_r8, "topics"."reply_count" AS t0_r9, "topics"."featured_user1_id" AS t0_r10, "topics"."featured_user2_id" AS t0_r11, "topics"."featured_user3_id" AS t0_r12, "topics"."deleted_at" AS t0_r13, "topics"."highest_post_number" AS t0_r14, "topics"."like_count" AS t0_r15, "topics"."incoming_link_count" AS t0_r16, "topics"."category_id" AS t0_r17, "topics"."visible" AS t0_r18, "topics"."moderator_posts_count" AS t0_r19, "topics"."closed" AS t0_r20, "topics"."archived" AS t0_r21, "topics"."bumped_at" AS t0_r22, "topics"."has_summary" AS t0_r23, "topics"."archetype" AS t0_r24, "topics"."featured_user4_id" AS t0_r25, "topics"."notify_moderators_count" AS t0_r26, "topics"."spam_count" AS t0_r27, "topics"."pinned_at" AS t0_r28, "topics"."score" AS t0_r29, "topics"."percent_rank" AS t0_r30, "topics"."subtype" AS t0_r31, "topics"."slug" AS t0_r32, "topics"."deleted_by_id" AS t0_r33, "topics"."participant_count" AS t0_r34, "topics"."word_count" AS t0_r35, "topics"."excerpt" AS t0_r36, "topics"."pinned_globally" AS t0_r37, "topics"."pinned_until" AS t0_r38, "topics"."fancy_title" AS t0_r39, "topics"."highest_staff_post_number" AS t0_r40, "topics"."featured_link" AS t0_r41, "topics"."reviewable_score" AS t0_r42, "topics"."image_upload_id" AS t0_r43, "topics"."slow_mode_seconds" AS t0_r44, "topics"."bannered_until" AS t0_r45, "topics"."external_id" AS t0_r46, "categories"."id" AS t1_r0, "categories"."name" AS t1_r1, "categories"."color" AS t1_r2, "categories"."topic_id" AS t1_r3, "categories"."topic_count" AS t1_r4, "categories"."created_at" AS t1_r5, "categories"."updated_at" AS t1_r6, "categories"."user_id" AS t1_r7, "categories"."topics_year" AS t1_r8, "categories"."topics_month" AS t1_r9, "categories"."topics_week" AS t1_r10, "categories"."slug" AS t1_r11, "categories"."description" AS t1_r12, "categories"."text_color" AS t1_r13, "categories"."read_restricted" AS t1_r14, "categories"."auto_close_hours" AS t1_r15, "categories"."post_count" AS t1_r16, "categories"."latest_post_id" AS t1_r17, "categories"."latest_topic_id" AS t1_r18, "categories"."position" AS t1_r19, "categories"."parent_category_id" AS t1_r20, "categories"."posts_year" AS t1_r21, "categories"."posts_month" AS t1_r22, "categories"."posts_week" AS t1_r23, "categories"."email_in" AS t1_r24, "categories"."email_in_allow_strangers" AS t1_r25, "categories"."topics_day" AS t1_r26, "categories"."posts_day" AS t1_r27, "categories"."allow_badges" AS t1_r28, "categories"."name_lower" AS t1_r29, "categories"."auto_close_based_on_last_post" AS t1_r30, "categories"."topic_template" AS t1_r31, "categories"."contains_messages" AS t1_r32, "categories"."sort_order" AS t1_r33, "categories"."sort_ascending" AS t1_r34, "categories"."uploaded_logo_id" AS t1_r35, "categories"."uploaded_background_id" AS t1_r36, "categories"."topic_featured_link_allowed" AS t1_r37, "categories"."all_topics_wiki" AS t1_r38, "categories"."show_subcategory_list" AS t1_r39, "categories"."num_featured_topics" AS t1_r40, "categories"."default_view" AS t1_r41, "categories"."subcategory_list_style" AS t1_r42, "categories"."default_top_period" AS t1_r43, "categories"."mailinglist_mirror" AS t1_r44, "categories"."minimum_required_tags" AS t1_r45, "categories"."navigate_to_first_post_after_read" AS t1_r46, "categories"."search_priority" AS t1_r47, "categories"."allow_global_tags" AS t1_r48, "categories"."reviewable_by_group_id" AS t1_r49, "categories"."read_only_banner" AS t1_r50, "categories"."default_list_filter" AS t1_r51, "categories"."allow_unlimited_owner_edits_on_first_post" AS t1_r52, "categories"."default_slow_mode_seconds" AS t1_r53, "categories"."uploaded_logo_dark_id" AS t1_r54 FROM "topics" LEFT OUTER JOIN "categories" ON "categories"."id" = "topics"."category_id" LEFT OUTER JOIN topic_users AS tu ON (topics.id = tu.topic_id AND tu.user_id = 29) LEFT JOIN category_users ON category_users.category_id = topics.category_id AND category_users.user_id = 29 WHERE "topics"."deleted_at" IS NULL AND (topics.archetype <> 'private_message') AND (COALESCE(categories.topic_id, 0) <> topics.id) AND (COALESCE(tu.notification_level,1) > 0) AND (topics.category_id = -1
OR
(COALESCE(category_users.notification_level, 1) <> 0 AND (topics.category_id IS NULL OR topics.category_id NOT IN(-1)))
OR tu.notification_level > 1) AND (pinned_globally AND pinned_at IS NOT NULL AND (topics.pinned_at > tu.cleared_pinned_at OR tu.cleared_pinned_at IS NULL)) ORDER BY "topics"."pinned_at" DESC LIMIT 30
SELECT "topic_tags".* FROM "topic_tags" WHERE "topic_tags"."topic_id" = 7
SELECT "topics"."id" AS t0_r0, "topics"."title" AS t0_r1, "topics"."last_posted_at" AS t0_r2, "topics"."created_at" AS t0_r3, "topics"."updated_at" AS t0_r4, "topics"."views" AS t0_r5, "topics"."posts_count" AS t0_r6, "topics"."user_id" AS t0_r7, "topics"."last_post_user_id" AS t0_r8, "topics"."reply_count" AS t0_r9, "topics"."featured_user1_id" AS t0_r10, "topics"."featured_user2_id" AS t0_r11, "topics"."featured_user3_id" AS t0_r12, "topics"."deleted_at" AS t0_r13, "topics"."highest_post_number" AS t0_r14, "topics"."like_count" AS t0_r15, "topics"."incoming_link_count" AS t0_r16, "topics"."category_id" AS t0_r17, "topics"."visible" AS t0_r18, "topics"."moderator_posts_count" AS t0_r19, "topics"."closed" AS t0_r20, "topics"."archived" AS t0_r21, "topics"."bumped_at" AS t0_r22, "topics"."has_summary" AS t0_r23, "topics"."archetype" AS t0_r24, "topics"."featured_user4_id" AS t0_r25, "topics"."notify_moderators_count" AS t0_r26, "topics"."spam_count" AS t0_r27, "topics"."pinned_at" AS t0_r28, "topics"."score" AS t0_r29, "topics"."percent_rank" AS t0_r30, "topics"."subtype" AS t0_r31, "topics"."slug" AS t0_r32, "topics"."deleted_by_id" AS t0_r33, "topics"."participant_count" AS t0_r34, "topics"."word_count" AS t0_r35, "topics"."excerpt" AS t0_r36, "topics"."pinned_globally" AS t0_r37, "topics"."pinned_until" AS t0_r38, "topics"."fancy_title" AS t0_r39, "topics"."highest_staff_post_number" AS t0_r40, "topics"."featured_link" AS t0_r41, "topics"."reviewable_score" AS t0_r42, "topics"."image_upload_id" AS t0_r43, "topics"."slow_mode_seconds" AS t0_r44, "topics"."bannered_until" AS t0_r45, "topics"."external_id" AS t0_r46, "categories"."id" AS t1_r0, "categories"."name" AS t1_r1, "categories"."color" AS t1_r2, "categories"."topic_id" AS t1_r3, "categories"."topic_count" AS t1_r4, "categories"."created_at" AS t1_r5, "categories"."updated_at" AS t1_r6, "categories"."user_id" AS t1_r7, "categories"."topics_year" AS t1_r8, "categories"."topics_month" AS t1_r9, "categories"."topics_week" AS t1_r10, "categories"."slug" AS t1_r11, "categories"."description" AS t1_r12, "categories"."text_color" AS t1_r13, "categories"."read_restricted" AS t1_r14, "categories"."auto_close_hours" AS t1_r15, "categories"."post_count" AS t1_r16, "categories"."latest_post_id" AS t1_r17, "categories"."latest_topic_id" AS t1_r18, "categories"."position" AS t1_r19, "categories"."parent_category_id" AS t1_r20, "categories"."posts_year" AS t1_r21, "categories"."posts_month" AS t1_r22, "categories"."posts_week" AS t1_r23, "categories"."email_in" AS t1_r24, "categories"."email_in_allow_strangers" AS t1_r25, "categories"."topics_day" AS t1_r26, "categories"."posts_day" AS t1_r27, "categories"."allow_badges" AS t1_r28, "categories"."name_lower" AS t1_r29, "categories"."auto_close_based_on_last_post" AS t1_r30, "categories"."topic_template" AS t1_r31, "categories"."contains_messages" AS t1_r32, "categories"."sort_order" AS t1_r33, "categories"."sort_ascending" AS t1_r34, "categories"."uploaded_logo_id" AS t1_r35, "categories"."uploaded_background_id" AS t1_r36, "categories"."topic_featured_link_allowed" AS t1_r37, "categories"."all_topics_wiki" AS t1_r38, "categories"."show_subcategory_list" AS t1_r39, "categories"."num_featured_topics" AS t1_r40, "categories"."default_view" AS t1_r41, "categories"."subcategory_list_style" AS t1_r42, "categories"."default_top_period" AS t1_r43, "categories"."mailinglist_mirror" AS t1_r44, "categories"."minimum_required_tags" AS t1_r45, "categories"."navigate_to_first_post_after_read" AS t1_r46, "categories"."search_priority" AS t1_r47, "categories"."allow_global_tags" AS t1_r48, "categories"."reviewable_by_group_id" AS t1_r49, "categories"."read_only_banner" AS t1_r50, "categories"."default_list_filter" AS t1_r51, "categories"."allow_unlimited_owner_edits_on_first_post" AS t1_r52, "categories"."default_slow_mode_seconds" AS t1_r53, "categories"."uploaded_logo_dark_id" AS t1_r54 FROM "topics" LEFT OUTER JOIN "categories" ON "categories"."id" = "topics"."category_id" LEFT OUTER JOIN topic_users AS tu ON (topics.id = tu.topic_id AND tu.user_id = 29) LEFT JOIN category_users ON category_users.category_id = topics.category_id AND category_users.user_id = 29 WHERE "topics"."deleted_at" IS NULL AND (topics.archetype <> 'private_message') AND (COALESCE(categories.topic_id, 0) <> topics.id) AND (COALESCE(tu.notification_level,1) > 0) AND (topics.category_id = -1
OR
(COALESCE(category_users.notification_level, 1) <> 0 AND (topics.category_id IS NULL OR topics.category_id NOT IN(-1)))
OR tu.notification_level > 1) AND (NOT ( pinned_globally AND pinned_at IS NOT NULL AND (topics.pinned_at > tu.cleared_pinned_at OR tu.cleared_pinned_at IS NULL) )) ORDER BY topics.bumped_at DESC LIMIT 30
SELECT "topic_tags".* FROM "topic_tags" WHERE "topic_tags"."topic_id" IN (477, 481, 480, 479, 478, 467, 466, 230, 209, 183, 173, 179, 168, 139, 102, 144, 150, 118, 126, 88, 63, 46, 117, 171, 45, 77, 154, 158, 43, 79)
SELECT "tags"."id", "tags"."name", "tags"."created_at", "tags"."updated_at", "tags"."pm_topic_count", "tags"."target_tag_id", "tags"."description", "tags"."public_topic_count", "tags"."staff_topic_count" FROM "tags" WHERE "tags"."id" IN (10, 20, 26, 7, 27, 28, 30, 19, 9, 4, 15, 29, 14, 18, 11, 25, 1, 21, 8, 22, 5, 32)
```
We end up with queries that are much more efficient as those queries can
effectively use the indexes.
If you're familiar with how Rails works and are comfortable setting up your own environment, you can also try out the Discourse Advanced Developer Guide, which is aimed primarily at Ubuntu and macOS environments.
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
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:
Please read the complete mission statements on discourse.org. Yes we actually believe this stuff; you should too.
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.
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:
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.
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93cc9276ea
