Active Record Query Logs¶ ↑

Automatically append comments to SQL queries with runtime information tags. This can be used to trace troublesome SQL statements back to the application code that generated these statements.

Query logs can be enabled via Rails configuration in config/application.rb or an initializer:

config.active_record.query_log_tags_enabled = true

By default the name of the application, the name and action of the controller, or the name of the job are logged. The default format is SQLCommenter. The tags shown in a query comment can be configured via Rails configuration:

config.active_record.query_log_tags = [ :application, :controller, :action, :job ]

Active Record defines default tags available for use:

• application

• pid

• socket

• db_host

• database

• source_location

WARNING: Calculating the source_location of a query can be slow, so you should consider its impact if using it in a production environment.

Also see config.active_record.verbose_query_logs.

Action Controller adds default tags when loaded:

• controller

• action

• namespaced_controller

Active Job adds default tags when loaded:

• job

New comment tags can be defined by adding them in a Hash to the tags Array. Tags can have dynamic content by setting a Proc or lambda value in the Hash, and can reference any value stored by Rails in the context object. ActiveSupport::CurrentAttributes can be used to store application values. Tags with nil values are omitted from the query comment.

context includes the following keys:

• controller - current Action Controller instance, if available

• job - current Active Job instance, if available

• connection - current database connection

• sql - current SQL query

Escaping is performed on the string returned, however untrusted user input should not be used.

Example:

config.active_record.query_log_tags = [
  :namespaced_controller,
  :action,
  :job,
  {
    request_id: ->(context) { context[:controller]&.request&.request_id },
    job_id: ->(context) { context[:job]&.job_id },
    tenant_id: -> { Current.tenant&.id },
    static: "value",
  },
]

WARNING: SQL query can contain sensitive data and using :sql directly as a query log tag is unsafe because it will log the query unfiltered.

Example:

# unsafe
config.active_record.query_log_tags = [:sql]

# safe
config.active_record.query_log_tags = [sql_length: ->(context) { context[:sql].length } ]

By default the name of the application, the name and action of the controller, or the name of the job are logged using the SQLCommenter format. This can be changed via config.active_record.query_log_tags_format

The format can also be overridden per connection pool through the query_log_tags key of a database.yml entry. Connections checked out from that pool use the configured format, while setting query_log_tags to false instead opts the pool out of tagging entirely. Pools without any explicit configuration fall back to the global defaults:

production:
  primary:
    database: primary
  analytics:
    database: analytics
    query_log_tags:
      format: sqlcommenter
  replica:
    database: replica
    replica: true
    query_log_tags: false

Tag comments can be prepended to the query:

config.active_record.query_log_tags_prepend_comment = true

Whether the comment is prepended can also be overridden per connection pool with a prepend_comment key under query_log_tags in a database.yml entry. Connections checked out from that pool use the configured value, while pools without any explicit configuration fall back to the global default:

production:
  primary:
    database: primary
  analytics:
    database: analytics
    query_log_tags:
      prepend_comment: true

For applications where the content will not change during the lifetime of the request or job execution, the tags can be cached for reuse in every query:

config.active_record.cache_query_log_tags = true