Improve performance of Search API (Advanced): users scope
## Summary
In https://gitlab.com/groups/gitlab-org/-/epics/3166 a performance issue was raised around the response time of the Advanced Search API. This issue deals specifically with the `users` scope, at the Global, Group, and Project levels. Below are results of a performance test that was run on the [10k reference architecture](https://docs.gitlab.com/ee/administration/scaling/#up-to-10000-users):
```
API - Global Search
✓ { endpoint:users }............: avg=8298.67ms min=31.19ms med=10539.07ms max=12639.17ms p(90)=11797.77ms p(95)=11981.41ms
```
```
API - Group Search
✓ { endpoint:users }............: avg=11049.06ms min=573.63ms med=10853.37ms max=23765.19ms p(90)=17645.64ms p(95)=19981.77ms
```
```
API - Project Search
✓ { endpoint:users }............: avg=3262.30ms min=198.66ms med=3525.94ms max=7031.63ms p(90)=4491.66ms p(95)=4967.65ms
```
## Improvements
As seen [here](https://gitlab.com/gitlab-org/gitlab/-/blob/master/ee/lib/gitlab/elastic/search_results.rb#L14), this scope does not query Elasticsearch. Rather, the database is used for search, via the [`UsersFinder`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/finders/users_finder.rb).
#### Global
<details>
<summary>Queries</summary>
```
Started GET "/api/v4/search?scope=users&search=reported"
PersonalAccessToken Load (0.3ms) SELECT "personal_access_tokens".* FROM "personal_access_tokens" WHERE "personal_access_tokens"."token_digest" = '' LIMIT 1
↳ app/models/concerns/token_authenticatable_strategies/digest.rb:8:in `find_token_authenticatable'
User Load (0.5ms) SELECT "users".* FROM "users" WHERE "users"."id" = 1 LIMIT 1
↳ lib/gitlab/auth/auth_finders.rb:103:in `find_user_from_access_token'
License Load (0.2ms) SELECT "licenses".* FROM "licenses" ORDER BY "licenses"."id" DESC LIMIT 1
↳ ee/app/models/license.rb:268:in `load_license'
User Load (0.9ms) SELECT "users".* FROM "users" WHERE (("users"."name" ILIKE '%reported%' OR "users"."username" ILIKE '%reported%') OR "users"."email" = 'reported') ORDER BY CASE
WHEN users.name = 'reported' THEN 0
WHEN users.username = 'reported' THEN 1
WHEN users.email = 'reported' THEN 2
ELSE 3
END
, "users"."name" ASC LIMIT 20 OFFSET 0
↳ app/services/search_service.rb:75:in `redact_unauthorized_results'
(0.5ms) SELECT COUNT(*) FROM "users" WHERE (("users"."name" ILIKE '%reported%' OR "users"."username" ILIKE '%reported%') OR "users"."email" = 'reported') AND 1=1
↳ lib/gitlab/pagination/offset_pagination.rb:47:in `add_pagination_headers'
User Load (0.8ms) SELECT "users".* FROM "users" WHERE (("users"."name" ILIKE '%reported%' OR "users"."username" ILIKE '%reported%') OR "users"."email" = 'reported') AND 1=1 ORDER BY CASE
WHEN users.name = 'reported' THEN 0
WHEN users.username = 'reported' THEN 1
WHEN users.email = 'reported' THEN 2
ELSE 3
END
, "users"."name" ASC LIMIT 20 OFFSET 0
↳ lib/api/search.rb:75:in `block (2 levels) in <class:Search>'
```
</details>
It looks like the same query for Users is being run twice. The only difference between the queries is that the second one has `AND 1=1`.
#### Group
<details>
<summary>Queries</summary>
```
Started GET "/api/v4/groups/28/search?scope=users&search=root"
ApplicationSetting Load (0.8ms) SELECT "application_settings".* FROM "application_settings" ORDER BY "application_settings"."id" DESC LIMIT 1
↳ app/models/concerns/cacheable_attributes.rb:19:in `current_without_cache'
PersonalAccessToken Load (0.2ms) SELECT "personal_access_tokens".* FROM "personal_access_tokens" WHERE "personal_access_tokens"."token_digest" = '' LIMIT 1
↳ app/models/concerns/token_authenticatable_strategies/digest.rb:8:in `find_token_authenticatable'
User Load (0.5ms) SELECT "users".* FROM "users" WHERE "users"."id" = 1 LIMIT 1
↳ lib/gitlab/auth/auth_finders.rb:103:in `find_user_from_access_token'
(0.2ms) SELECT "features"."key" FROM "features"
↳ lib/feature.rb:15:in `feature_names'
License Load (0.2ms) SELECT "licenses".* FROM "licenses" ORDER BY "licenses"."id" DESC LIMIT 1
↳ ee/app/models/license.rb:268:in `load_license'
Group Load (0.4ms) SELECT "namespaces".* FROM "namespaces" WHERE "namespaces"."type" = 'Group' AND "namespaces"."id" = 28 LIMIT 1
↳ lib/api/helpers.rb:128:in `find_group'
IpRestriction Load (0.2ms) SELECT "ip_restrictions".* FROM "ip_restrictions" WHERE "ip_restrictions"."group_id" = 28
↳ ee/lib/gitlab/ip_restriction/enforcer.rb:31:in `allows_address?'
Group Load (0.4ms) SELECT "namespaces".* FROM "namespaces" WHERE "namespaces"."type" = 'Group' AND "namespaces"."id" = 28 LIMIT 1
↳ app/services/search_service.rb:34:in `group'
Route Load (0.3ms) SELECT "routes".* FROM "routes" WHERE "routes"."source_id" = 28 AND "routes"."source_type" = 'Namespace' LIMIT 1
↳ app/models/concerns/routable.rb:77:in `full_path'
(0.9ms) SELECT "projects"."id" FROM "projects" INNER JOIN routes rs ON rs.source_id = projects.id AND rs.source_type = 'Project' WHERE (EXISTS (SELECT 1 FROM "project_authorizations" WHERE "project_authorizations"."user_id" = 1 AND (project_authorizations.project_id = projects.id)) OR projects.visibility_level IN (0,10,20)) AND "projects"."archived" = FALSE AND (rs.path LIKE 'h5bp/%') ORDER BY "projects"."id" DESC
↳ ee/app/services/ee/search/group_service.rb:15:in `elastic_projects'
User Load (10.5ms) SELECT "users".* FROM "users" WHERE (("users"."name" ILIKE '%root%' OR "users"."username" ILIKE '%root%') OR "users"."email" = 'root') AND "users"."id" IN (SELECT "users"."id" FROM ((SELECT "users".* FROM "users" WHERE "users"."id" IN (SELECT "members"."user_id" FROM "members" LEFT OUTER JOIN "users" ON "members"."user_id" = "users"."id" WHERE "members"."type" = 'GroupMember' AND "members"."source_type" = 'Namespace' AND "users"."state" = 'active' AND "members"."requested_at" IS NULL AND "members"."source_id" IN (WITH RECURSIVE "base_and_ancestors" AS ((SELECT "namespaces".* FROM "namespaces" WHERE "namespaces"."type" = 'Group' AND "namespaces"."id" = 28)
UNION
(SELECT "namespaces".* FROM "namespaces", "base_and_ancestors" WHERE "namespaces"."type" = 'Group' AND "namespaces"."id" = "base_and_ancestors"."parent_id")), "base_and_descendants" AS ((SELECT "namespaces".* FROM "namespaces" WHERE "namespaces"."type" = 'Group' AND "namespaces"."id" = 28)
UNION
(SELECT "namespaces".* FROM "namespaces", "base_and_descendants" WHERE "namespaces"."type" = 'Group' AND "namespaces"."parent_id" = "base_and_descendants"."id")) SELECT "namespaces"."id" FROM ((SELECT "namespaces".* FROM "base_and_ancestors" AS "namespaces" WHERE "namespaces"."type" = 'Group')
UNION
(SELECT "namespaces".* FROM "base_and_descendants" AS "namespaces" WHERE "namespaces"."type" = 'Group')) namespaces WHERE "namespaces"."type" = 'Group')))
UNION
(SELECT "users".* FROM "users" INNER JOIN "members" ON "members"."source_type" = 'Project' AND "members"."user_id" = "users"."id" AND "members"."type" = 'ProjectMember' AND "members"."requested_at" IS NULL INNER JOIN "projects" ON "projects"."id" = "members"."source_id" INNER JOIN "namespaces" ON "namespaces"."id" = "projects"."namespace_id" AND "namespaces"."type" = 'Group' WHERE "namespaces"."id" IN (WITH RECURSIVE "base_and_descendants" AS ((SELECT "namespaces".* FROM "namespaces" WHERE "namespaces"."type" = 'Group' AND "namespaces"."id" = 28)
UNION
(SELECT "namespaces".* FROM "namespaces", "base_and_descendants" WHERE "namespaces"."type" = 'Group' AND "namespaces"."parent_id" = "base_and_descendants"."id")) SELECT "id" FROM "base_and_descendants" AS "namespaces"))) users) AND "users"."id" IN (SELECT members.user_id FROM "namespaces" INNER JOIN "members" ON "members"."source_type" = 'Namespace' AND "members"."source_id" = "namespaces"."id" AND "members"."source_type" = 'Namespace' AND "members"."type" = 'GroupMember' AND "members"."requested_at" IS NULL INNER JOIN "users" ON "users"."id" = "members"."user_id" WHERE "namespaces"."type" = 'Group' ORDER BY "namespaces"."id" DESC) ORDER BY CASE
WHEN users.name = 'root' THEN 0
WHEN users.username = 'root' THEN 1
WHEN users.email = 'root' THEN 2
ELSE 3
END
, "users"."name" ASC LIMIT 20 OFFSET 0
↳ app/services/search_service.rb:75:in `redact_unauthorized_results'
(8.7ms) SELECT COUNT(*) FROM "users" WHERE (("users"."name" ILIKE '%root%' OR "users"."username" ILIKE '%root%') OR "users"."email" = 'root') AND "users"."id" IN (SELECT "users"."id" FROM ((SELECT "users".* FROM "users" WHERE "users"."id" IN (SELECT "members"."user_id" FROM "members" LEFT OUTER JOIN "users" ON "members"."user_id" = "users"."id" WHERE "members"."type" = 'GroupMember' AND "members"."source_type" = 'Namespace' AND "users"."state" = 'active' AND "members"."requested_at" IS NULL AND "members"."source_id" IN (WITH RECURSIVE "base_and_ancestors" AS ((SELECT "namespaces".* FROM "namespaces" WHERE "namespaces"."type" = 'Group' AND "namespaces"."id" = 28)
UNION
(SELECT "namespaces".* FROM "namespaces", "base_and_ancestors" WHERE "namespaces"."type" = 'Group' AND "namespaces"."id" = "base_and_ancestors"."parent_id")), "base_and_descendants" AS ((SELECT "namespaces".* FROM "namespaces" WHERE "namespaces"."type" = 'Group' AND "namespaces"."id" = 28)
UNION
(SELECT "namespaces".* FROM "namespaces", "base_and_descendants" WHERE "namespaces"."type" = 'Group' AND "namespaces"."parent_id" = "base_and_descendants"."id")) SELECT "namespaces"."id" FROM ((SELECT "namespaces".* FROM "base_and_ancestors" AS "namespaces" WHERE "namespaces"."type" = 'Group')
UNION
(SELECT "namespaces".* FROM "base_and_descendants" AS "namespaces" WHERE "namespaces"."type" = 'Group')) namespaces WHERE "namespaces"."type" = 'Group')))
UNION
(SELECT "users".* FROM "users" INNER JOIN "members" ON "members"."source_type" = 'Project' AND "members"."user_id" = "users"."id" AND "members"."type" = 'ProjectMember' AND "members"."requested_at" IS NULL INNER JOIN "projects" ON "projects"."id" = "members"."source_id" INNER JOIN "namespaces" ON "namespaces"."id" = "projects"."namespace_id" AND "namespaces"."type" = 'Group' WHERE "namespaces"."id" IN (WITH RECURSIVE "base_and_descendants" AS ((SELECT "namespaces".* FROM "namespaces" WHERE "namespaces"."type" = 'Group' AND "namespaces"."id" = 28)
UNION
(SELECT "namespaces".* FROM "namespaces", "base_and_descendants" WHERE "namespaces"."type" = 'Group' AND "namespaces"."parent_id" = "base_and_descendants"."id")) SELECT "id" FROM "base_and_descendants" AS "namespaces"))) users) AND "users"."id" IN (SELECT members.user_id FROM "namespaces" INNER JOIN "members" ON "members"."source_type" = 'Namespace' AND "members"."source_id" = "namespaces"."id" AND "members"."source_type" = 'Namespace' AND "members"."type" = 'GroupMember' AND "members"."requested_at" IS NULL INNER JOIN "users" ON "users"."id" = "members"."user_id" WHERE "namespaces"."type" = 'Group' ORDER BY "namespaces"."id" DESC) AND 1=1
↳ lib/gitlab/pagination/offset_pagination.rb:47:in `add_pagination_headers'
User Load (9.6ms) SELECT "users".* FROM "users" WHERE (("users"."name" ILIKE '%root%' OR "users"."username" ILIKE '%root%') OR "users"."email" = 'root') AND "users"."id" IN (SELECT "users"."id" FROM ((SELECT "users".* FROM "users" WHERE "users"."id" IN (SELECT "members"."user_id" FROM "members" LEFT OUTER JOIN "users" ON "members"."user_id" = "users"."id" WHERE "members"."type" = 'GroupMember' AND "members"."source_type" = 'Namespace' AND "users"."state" = 'active' AND "members"."requested_at" IS NULL AND "members"."source_id" IN (WITH RECURSIVE "base_and_ancestors" AS ((SELECT "namespaces".* FROM "namespaces" WHERE "namespaces"."type" = 'Group' AND "namespaces"."id" = 28)
UNION
(SELECT "namespaces".* FROM "namespaces", "base_and_ancestors" WHERE "namespaces"."type" = 'Group' AND "namespaces"."id" = "base_and_ancestors"."parent_id")), "base_and_descendants" AS ((SELECT "namespaces".* FROM "namespaces" WHERE "namespaces"."type" = 'Group' AND "namespaces"."id" = 28)
UNION
(SELECT "namespaces".* FROM "namespaces", "base_and_descendants" WHERE "namespaces"."type" = 'Group' AND "namespaces"."parent_id" = "base_and_descendants"."id")) SELECT "namespaces"."id" FROM ((SELECT "namespaces".* FROM "base_and_ancestors" AS "namespaces" WHERE "namespaces"."type" = 'Group')
UNION
(SELECT "namespaces".* FROM "base_and_descendants" AS "namespaces" WHERE "namespaces"."type" = 'Group')) namespaces WHERE "namespaces"."type" = 'Group')))
UNION
(SELECT "users".* FROM "users" INNER JOIN "members" ON "members"."source_type" = 'Project' AND "members"."user_id" = "users"."id" AND "members"."type" = 'ProjectMember' AND "members"."requested_at" IS NULL INNER JOIN "projects" ON "projects"."id" = "members"."source_id" INNER JOIN "namespaces" ON "namespaces"."id" = "projects"."namespace_id" AND "namespaces"."type" = 'Group' WHERE "namespaces"."id" IN (WITH RECURSIVE "base_and_descendants" AS ((SELECT "namespaces".* FROM "namespaces" WHERE "namespaces"."type" = 'Group' AND "namespaces"."id" = 28)
UNION
(SELECT "namespaces".* FROM "namespaces", "base_and_descendants" WHERE "namespaces"."type" = 'Group' AND "namespaces"."parent_id" = "base_and_descendants"."id")) SELECT "id" FROM "base_and_descendants" AS "namespaces"))) users) AND "users"."id" IN (SELECT members.user_id FROM "namespaces" INNER JOIN "members" ON "members"."source_type" = 'Namespace' AND "members"."source_id" = "namespaces"."id" AND "members"."source_type" = 'Namespace' AND "members"."type" = 'GroupMember' AND "members"."requested_at" IS NULL INNER JOIN "users" ON "users"."id" = "members"."user_id" WHERE "namespaces"."type" = 'Group' ORDER BY "namespaces"."id" DESC) AND 1=1 ORDER BY CASE
WHEN users.name = 'root' THEN 0
WHEN users.username = 'root' THEN 1
WHEN users.email = 'root' THEN 2
ELSE 3
END
, "users"."name" ASC LIMIT 20 OFFSET 0
↳ lib/api/search.rb:96:in `block (2 levels) in <class:Search>'
```
</details>
The query to find Users seems quite complex, and does take longer relative to the Global query. Again, it looks like the same query is being performed twice.
#### Project
<details>
<summary>Queries</summary>
```
Started GET "/api/v4/projects/1/search?scope=users&search=root"
(0.4ms) SELECT EXTRACT(EPOCH FROM (now() - pg_last_xact_replay_timestamp()))::float as lag
↳ app/models/concerns/cacheable_attributes.rb:19:in `current_without_cache'
ApplicationSetting Load (2.5ms) SELECT "application_settings".* FROM "application_settings" ORDER BY "application_settings"."id" DESC LIMIT 1
↳ app/models/concerns/cacheable_attributes.rb:19:in `current_without_cache'
PersonalAccessToken Load (0.8ms) SELECT "personal_access_tokens".* FROM "personal_access_tokens" WHERE "personal_access_tokens"."token_digest" = '' LIMIT 1
↳ app/models/concerns/token_authenticatable_strategies/digest.rb:8:in `find_token_authenticatable'
User Load (2.5ms) SELECT "users".* FROM "users" WHERE "users"."id" = 1 LIMIT 1
↳ lib/gitlab/auth/auth_finders.rb:103:in `find_user_from_access_token'
(0.4ms) SELECT "features"."key" FROM "features"
↳ lib/feature.rb:15:in `feature_names'
License Load (0.4ms) SELECT "licenses".* FROM "licenses" ORDER BY "licenses"."id" DESC LIMIT 1
↳ ee/app/models/license.rb:268:in `load_license'
Project Load (3.1ms) SELECT "projects".* FROM "projects" WHERE "projects"."pending_delete" = FALSE AND "projects"."id" = 1 LIMIT 1
↳ lib/api/helpers.rb:108:in `find_project'
Group Load (1.4ms) SELECT "namespaces".* FROM "namespaces" WHERE "namespaces"."type" = 'Group' AND "namespaces"."id" = 22 AND "namespaces"."type" = 'Group' LIMIT 1
↳ ee/app/policies/ee/project_policy.rb:308:in `block (2 levels) in <module:ProjectPolicy>'
IpRestriction Load (0.4ms) SELECT "ip_restrictions".* FROM "ip_restrictions" WHERE "ip_restrictions"."group_id" = 22
↳ ee/lib/gitlab/ip_restriction/enforcer.rb:31:in `allows_address?'
Project Load (0.6ms) SELECT "projects".* FROM "projects" WHERE "projects"."id" = 1 LIMIT 1
↳ app/services/search_service.rb:20:in `project'
Route Load (0.6ms) SELECT "routes".* FROM "routes" WHERE "routes"."source_id" = 1 AND "routes"."source_type" = 'Project' LIMIT 1
↳ app/models/concerns/routable.rb:77:in `full_path'
User Load (2.7ms) SELECT "users".* FROM "users" WHERE (("users"."name" ILIKE '%root%' OR "users"."username" ILIKE '%root%') OR "users"."email" = 'root') AND "users"."id" IN (SELECT "users"."id" FROM "users" INNER JOIN "project_authorizations" ON "users"."id" = "project_authorizations"."user_id" WHERE "project_authorizations"."project_id" = 1) ORDER BY CASE
WHEN users.name = 'root' THEN 0
WHEN users.username = 'root' THEN 1
WHEN users.email = 'root' THEN 2
ELSE 3
END
, "users"."name" ASC LIMIT 20 OFFSET 0
↳ app/services/search_service.rb:75:in `redact_unauthorized_results'
(1.2ms) SELECT COUNT(*) FROM "users" WHERE (("users"."name" ILIKE '%root%' OR "users"."username" ILIKE '%root%') OR "users"."email" = 'root') AND "users"."id" IN (SELECT "users"."id" FROM "users" INNER JOIN "project_authorizations" ON "users"."id" = "project_authorizations"."user_id" WHERE "project_authorizations"."project_id" = 1) AND 1=1
↳ lib/gitlab/pagination/offset_pagination.rb:47:in `add_pagination_headers'
User Load (1.4ms) SELECT "users".* FROM "users" WHERE (("users"."name" ILIKE '%root%' OR "users"."username" ILIKE '%root%') OR "users"."email" = 'root') AND "users"."id" IN (SELECT "users"."id" FROM "users" INNER JOIN "project_authorizations" ON "users"."id" = "project_authorizations"."user_id" WHERE "project_authorizations"."project_id" = 1) AND 1=1 ORDER BY CASE
WHEN users.name = 'root' THEN 0
WHEN users.username = 'root' THEN 1
WHEN users.email = 'root' THEN 2
ELSE 3
END
, "users"."name" ASC LIMIT 20 OFFSET 0
↳ lib/api/search.rb:117:in `block (2 levels) in <class:Search>'
```
</details>
Same issue with duplicate query.
issue
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