Question

I have a select statement,

SELECT `metrics`.* 
FROM `metrics` 
WHERE `metrics`.`engine` = 0 
  AND (`metrics`.connection_id = 27874) 
  AND (`metrics`.`id` > 181586235) 
ORDER BY `metrics`.`id` ASC LIMIT 1000

which is generated by find_each being called on a relation (e.g. metric.engines.find_each). This select statement scans 15 million records each time it is run.

I’d like to make this lighter on the database by telling the query only to look for a range of metrics.ids (e.g. metrics.id > 1 AND metrics.id < 1000).

Is there a way to do this with find_each?

Answer 1

find_each can be applied to scopes like all finder methods:

Metric.where("metrics.id between 1 and 1000"]).find_each { ... }

EDIT: If you need to process all records but don’t want to load them all at once, you can use the find_in_batches method:

Metric.find_in_batches do |batch|
  batch.each { ... }
end