PERF: Improve performance of queries when loading a topic list (#22949)

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.

lib/topic_query.rb

@@ -750,7 +750,9 @@ class TopicQuery
     end
 
     if SiteSetting.tagging_enabled
-      result = result.includes(:tags)
+      # Use `preload` here instead since `includes` can end up calling `eager_load` which can unnecessarily lead to
+      # joins on the `topic_tags` and `tags` table leading to a much slower query.
+      result = result.preload(:tags)
       result = filter_by_tags(result)
     end