62 lines
2.3 KiB
Markdown
62 lines
2.3 KiB
Markdown
---
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stage: Data Stores
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group: Database
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info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
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---
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# Database query comments with Marginalia
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The [Marginalia gem](https://github.com/basecamp/marginalia) is used to add
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query comments containing application related context information to PostgreSQL
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queries generated by ActiveRecord.
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It is very useful for tracing problematic queries back to the application source.
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An engineer during an on-call incident has the full context of a query
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and its application source from the comments.
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## Metadata information in comments
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Queries generated from **Rails** include the following metadata in comments:
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- `application`
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- `correlation_id`
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- `endpoint_id`
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- `line`
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Queries generated from **Sidekiq** workers include the following metadata
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in comments:
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- `application`
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- `jid`
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- `correlation_id`
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- `endpoint_id`
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- `line`
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`endpoint_id` is a single field that can represent any endpoint in the application:
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- For Rails controllers, it's the controller and action. For example, `Projects::BlobController#show`.
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- For Grape API endpoints, it's the route. For example, `/api/:version/users/:id`.
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- For Sidekiq workers, it's the worker class name. For example, `UserStatusCleanup::BatchWorker`.
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`line` is not present in production logs due to the additional overhead required.
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Examples of queries with comments:
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- Rails:
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```sql
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/*application:web,controller:blob,action:show,correlation_id:01EZVMR923313VV44ZJDJ7PMEZ,endpoint_id:Projects::BlobController#show*/ SELECT "routes".* FROM "routes" WHERE "routes"."source_id" = 75 AND "routes"."source_type" = 'Namespace' LIMIT 1
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```
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- Grape:
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```sql
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/*application:web,correlation_id:01EZVN0DAYGJF5XHG9N4VX8FAH,endpoint_id:/api/:version/users/:id*/ SELECT COUNT(*) FROM "users" INNER JOIN "user_follow_users" ON "users"."id" = "user_follow_users"."followee_id" WHERE "user_follow_users"."follower_id" = 1
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```
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- Sidekiq:
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```sql
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/*application:sidekiq,correlation_id:df643992563683313bc0a0288fb55e23,jid:15fbc506590c625d7664b074,endpoint_id:UserStatusCleanup::BatchWorker,line:/app/workers/user_status_cleanup/batch_worker.rb:19:in `perform'*/ SELECT $1 AS one FROM "user_statuses" WHERE "user_statuses"."clear_status_at" <= $2 LIMIT $3
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```
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