57 lines
1.8 KiB
Markdown
57 lines
1.8 KiB
Markdown
# 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 will have 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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- `controller`
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- `action`
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- `correlation_id`
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- `line`
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Queries generated from **Sidekiq** workers will include the following metadata
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in comments:
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- `application`
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- `jid`
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- `job_class`
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- `correlation_id`
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- `line`
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Examples of queries with comments as observed in `development.log`:
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1. Rails:
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```sql
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SELECT "project_features".* FROM "project_features" WHERE "project_features"."project_id" = $1 LIMIT $2 [["project_id", 5], ["LIMIT", 1]] /*application:web,controller:jobs,action:trace,correlation_id:rYF4mey9CH3,line:/app/policies/project_policy.rb:504:in `feature_available?'*/
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```
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1. Sidekiq:
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```sql
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SELECT "ci_pipelines".* FROM "ci_pipelines" WHERE "ci_pipelines"."id" = $1 LIMIT $2 [["id", 64], ["LIMIT", 1]] /*application:sidekiq,jid:e7d6668a39a991e323009833,job_class:ExpireJobCacheWorker,correlation_id:rYF4mey9CH3,line:/app/workers/expire_job_cache_worker.rb:14:in `perform'*/
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```
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## Enable/Disable the feature
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Enabling or disabling the feature requires a **restart/SIGHUP** of the Web and
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Sidekiq workers, as the feature flag's state is memoized upon starting up.
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The `feature_flag` for this feature is **disabled** by default. You can enable
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or disable it with:
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```ruby
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Feature.enable(:marginalia)
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Feature.disable(:marginalia)
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```
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