Mysql 5.5 Innodb慢插入查询问题

Question

I have a stored procedure which inserts around 3K rows in a temporary table. This SP used to take 3 seconds on Mysql 5.1 (windows desktop), the same SP was taking around 2 mins on Mysql 5.5.

I tried lot of things like optimizing innodb by changing innodb_buffer_pool_size etc but nothing worked and then I read something on stackoverflow which solved my problem.

START TRANSACTION; 
CALL sp();
COMMIT;

The above code solved the issue and now I am back to 3 secs execution time. Can someone please tell me what exactly is happening here. Why do I have to add start transaction in 5.5 for fast execution? Why didnt I need this in 5.1

Answer 1

I would guess it's due to autocommit being disabled by running

START TRANSACTION; 

You can verify it by disabling autocommit manually and then run your proc.

SET autocommit=0;

Answer 2

I added the following line in my mysql.ini file

innodb_flush_log_at_trx_commit=0

It seems to have solved the issue, the procedure runs fast now. Ideally innodb_flush_log_at_trx_commit should be 1 for ACID compliance.

Answer 3

When you insert a row into an InnoDB table, MySQL builds the primary_key and updates indexes for that row. This is done for each row and can slow down your inserts considerably. By wrapping them up in a transaction, you're essentially forcing it to first insert all the rows, and then rebuild keys and indexes in one shot. Hence the performance gain.