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MySQL - Speed of INSERT Queries
The time to insert a record consists approximately of:
Connect: (3)
Sending query to server: (2)
Parsing query: (2)
Inserting record: (1 x size of record)
Inserting indexes: (1 x number of indexes)
Close: (1)
where the numbers are somewhat proportional to the overall 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).
Some ways to speed up inserts:
If you are inserting many rows from the same client at the same time, use multiple value lists INSERT statements. This is
much faster (many times in some cases) than using separate INSERT statements.
If you are inserting a lot of rows from different clients, you can get higher speed by using the INSERT DELAYED statement.
Note that with MyISAM you can insert rows at the same time SELECTs are running if there are no deleted rows in the tables.
When loading a table from a text file, use LOAD DATA INFILE. This is usually 20 times faster than using a lot of INSERT
statements.
It is possible with some extra work to make LOAD DATA INFILE run even faster when the table has many indexes. Use the
following procedure:
Optionally create the table with CREATE TABLE. For example, using mysql or Perl-DBI.
Execute a FLUSH TABLES statement or the shell command mysqladmin flush-tables.
Use myisamchk --keys-used=0 -rq /path/to/db/tbl_name. This will remove all usage of all indexes from the table.
Insert data into the table with LOAD DATA INFILE. This will not update any indexes and will therefore be very fast.
If you are going to only read the table in the future, run myisampack on it to make it smaller.
Re-create the indexes with myisamchk -r -q /path/to/db/tbl_name. This will create the index tree in memory before writing it
to disk, which is much faster because it avoids lots of disk seeks. The resulting index tree is also perfectly balanced.
Execute a FLUSH TABLES statement or the shell command mysqladmin flush-tables.
This procedure will be built into LOAD DATA INFILE in some future version of MySQL.
You can speed up insertions by locking your tables:
mysql> LOCK TABLES a WRITE;
mysql> INSERT INTO a VALUES (1,23),(2,34),(4,33);
mysql> INSERT INTO a VALUES (8,26),(6,29);
mysql> UNLOCK TABLES;
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 an 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 for loading data.
To get some more speed for both LOAD DATA INFILE and INSERT, enlarge the key buffer.
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