MySQL optimizing INSERT speed being slowed down because of indices

Question

MySQL Docs say :

The size of the table slows down the insertion of indexes by log N, assuming B-tree indexes.

Does this mean that for insertion of each new row, the insertion speed will be slowed down by a factor of log N where N, I assume is number of rows? even if I insert all rows in just one query? i.e. :

INSERT INTO mytable VALUES (1,1,1), (2,2,2),  (3,3,3), .... ,(n,n,n)

Where n is ~70,000

I currently have ~1.47 million rows in a table with the following structure :

CREATE TABLE mytable (
   `id` INT,
   `value` MEDIUMINT(5),
   `date` DATE,
   PRIMARY_KEY(`id`,`date`)
) ENGINE = InnoDB

When I insert in the above mentioned fashion in a transaction, the commit time taken is ~275 seconds. How can I optimize this, since new data is to be added everyday and the insert time will just keep on slowing down.

Also, is there anything apart from just queries that might help? maybe some configuration settings?

Possible Method 1 - Removing Indices

I read that removing indices just before insert might help insert speed. And after inserts, I add the index again. But here the only index is primary key, and dropping it won't help much in my opinion. Also, while the primary key is dropped , all the select queries will be crippling slow.

I do not know of any other possible methods.

Edit : Here are a few tests on inserting ~60,000 rows in the table with ~1.47 mil rows:

Using the plain query described above : 146 seconds

Using MySQL's LOAD DATA infile : 145 seconds

Using MySQL's LOAD DATA infile and splitting the csv files as suggested by David Jashi in his answer: 136 seconds for 60 files with 1000 rows each, 136 seconds for 6 files with 10,000 rows each

Removing and re-adding primary key : key removal took 11 seconds, 0.8 seconds for inserting data BUT 153 seconds for re-adding primary key, totally taking ~165 seconds

Solution 1

If you want fast inserts, first thing you need is proper hardware. That assumes sufficient amount of RAM, an SSD instead of mechanical drives and rather powerful CPU.

Since you use InnoDB, what you want is to optimize it since default config is designed for slow and old machines.

Here's a great read about configuring InnoDB

After that, you need to know one thing - and that's how databases do their stuff internally, how hard drives work and so on. I'll simplify the mechanism in the following description:

A transaction is MySQL waiting for the hard drive to confirm that it wrote the data. That's why transactions are slow on mechanical drives, they can do 200-400 input-output operations per second. Translated, that means you can get 200ish insert queries per second using InnoDB on a mechanical drive. Naturally, this is simplified explanation, just to outline what's happening, it's not the full mechanism behind transaction.

Since a query, especially the one corresponding to size of your table, is relatively small in terms of bytes - you're effectively wasting precious IOPS on a single query.

If you wrap multiple queries (100 or 200 or more, there's no exact number, you have to test) in a single transaction and then commit it - you'll instantly achieve more writes per second.

Percona guys are achieving 15k inserts a second on a relatively cheap hardware. Even 5k inserts a second isn't bad. The table such as yours is small, I've done tests on a similar table (3 columns more) and I managed to get to 1 billion records without noticeable issues, using 16gb ram machine with a 240GB SSD (1 drive, no RAID, used for testing purposes).

TL;DR: - follow the link above, configure your server, get an SSD, wrap multiple inserts in 1 transactions and profit. And don't turn indexing off and then on, it's not applicable always, because at some point you will spend processing and IO time to build them.

Solution 2

Dropping index will sure help anyway. Also consider using LOAD DATA. You can find some comparison and benchmarks here

Also, when constructing PRIMARY KEY, use fields, that come first in your table, sequentially, i.e. switch places of second and third fields in structure.

Solution 3

If you are doing a bulk insert of a million rows, then dropping the index, doing the insert, and rebuilding the index will probably be faster. However, if your problem is that single row inserts are taking too long then you have other problems (like not enough memory) and dropping the index will not help much.

Solution 4

Building/rebuilding the index is what you're trying to speed up. If you must have this table/key structure, faster hardware and/or tweaking the server configuration to speed up the index build is likely the answer - be sure your server and settings are such that it can be accomplished in memory.

Otherwise, think about making trade-offs with the structure that would improve insert speeds. Alternatively, think about ways you can happily live with a 3 minute insert.

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