10.14 Factors affecting the speed of INSERT statements

The time to insert a record consists of:

  • Connect: (3)
  • Sending query to server: (2)
  • Parsing query: (2)
  • Inserting record: (1 x size of record)
  • Inserting indexes: (1 x indexes)
  • Close: (1)

Where (number) is proportional time. This does not take into consideration the initial overhead to open tables (which is done once for each concurrently-running query).

The size of the table slows down the insertion of indexes by N log N (B-trees).

You can speed up insertions by locking your table and/or using multiple value lists with INSERT statements. Using multiple value lists can be up to 5 times faster than using separate inserts.

mysql> INSERT INTO a VALUES (1,23),(2,34),(4,33);
mysql> INSERT INTO a VALUES (8,26),(6,29);

The main speed difference is that the index buffer is flushed to disk only once, after all INSERT statements have completed. Normally there would be as many index buffer flushes as there are different INSERT statements. Locking is not needed if you can insert all rows with a single statement.

Locking will also lower the total time of multi-connection tests, but the maximum wait time for some threads will go up (because they wait for locks). For example:

thread 1 does 1000 inserts
thread 2, 3, and 4 does 1 insert
thread 5 does 1000 inserts

If you don't use locking, 2, 3 and 4 will finish before 1 and 5. If you use locking, 2, 3 and 4 probably will not finish before 1 or 5, but the total time should be about 40% faster.

As INSERT, UPDATE and DELETE operations are very fast in MySQL, you will obtain better overall performance by adding locks around everything that does more than about 5 inserts or updates in a row. If you do very many inserts in a row, you could do a LOCK TABLES followed by a UNLOCK TABLES once in a while (about each 1000 rows) to allow other threads access to the table. This would still result in a nice performance gain.

Of course, LOAD DATA INFILE is much faster still.

If you are inserting a lot of rows from different clients, you can get higher speed by using the INSERT DELAYED statement. INSERT.