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Why does MySQL higher limit offset slow the query?
The higher LIMIT offset with SELECT, the slower the query becomes, when using ORDER BY *primary_key* 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?
When to use limit 0, 30 in MySQL?
Logically speaking, in the LIMIT 0, 30 version, only 30 rows need to be retrieved. In the LIMIT 10000, 30 version, 10000 rows are evaluated and 30 rows are returned. There can be some optimization can be done my the data-reading process, but consider the following:
How many rows does MySQL have to fetch to return 30?
Although it might be that way in actuality, MySQL cannot assume that there are no holes/gaps/deleted ids. So, as bobs noted, MySQL will have to fetch 10000 rows (or traverse through 10000th entries of the index on id) before finding the 30 to return.
Why does MySQL not go to The 10000th record?
MySQL cannot go directly to the 10000th record (or the 80000th byte as your suggesting) because it cannot assume that it’s packed/ordered like that (or that it has continuous values in 1 to 10000). Although it might be that way in actuality, MySQL cannot assume that there are no holes/gaps/deleted ids.
Why is order by with limit and offset slow-faster?
We tested the following OFFSET values with the following query, to present the performance deterioration as the OFFSET grows. The query was executed on a table that holds user performed events (an analytics table) with 150,000 records. The data is real user information and not auto generated.
How does an ORDER BY clause affect the query plan?
An ORDER BY clause can affect the query plan, because if there is an index that can provide the results in the order that matches the ORDER BY clause, then the optimizer may choose to use it. Because of that, the access order may change, which means most of the query plan will change.
When do you change the access order in a query plan?
Because of that, the access order may change, which means most of the query plan will change. In you inspect the query plan before and after adding the ORDER BY clause you are bound to see are rather big difference.
Is it possible to have a zero offset in MySQL?
So you can always have a ZERO offset. You will be amazed by the performance improvement. MySQL cannot go directly to the 10000th record (or the 80000th byte as your suggesting) because it cannot assume that it’s packed/ordered like that (or that it has continuous values in 1 to 10000).
How can I improve the performance of my SQL query?
Yes, you can improve query performance simply by replacing your SELECT * with actual column names. Do not use * in your SQL queries, instead, use actual column names that you want to return . The database may scan column names and replace * with actual columns of the table.
When to use the offset capability in MySQL?
This query should be extremely quick, because it’s using a covering index. We do not recommend using the OFFSET capability in MySQL to implement paging capabilities. When data grows, you’ll probably start noticing performance issues. Instead, consider using the Seek Method described above.