Mysql – Why does MYSQL higher LIMIT offset slow the query down

limitMySQLperformancesql-order-by

Scenario in short: A table with more than 16 million records [2GB in size]. The higher LIMIT offset with SELECT, the slower the query becomes, when using ORDER BY *primary_key*

So 

SELECT * FROM large ORDER BY `id`  LIMIT 0, 30

takes far less than 

SELECT * FROM large ORDER BY `id` LIMIT 10000, 30

That only orders 30 records and same eitherway. So it's not the overhead from ORDER BY.
Now when fetching the latest 30 rows it takes around 180 seconds. How can I optimize that simple query?

Best Answer

I had the exact same problem myself. Given the fact that you want to collect a large amount of this data and not a specific set of 30 you'll be probably running a loop and incrementing the offset by 30.

So what you can do instead is:

  1. Hold the last id of a set of data(30) (e.g. lastId = 530)
  2. Add the condition WHERE id > lastId limit 0,30

So you can always have a ZERO offset. You will be amazed by the performance improvement.

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