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I have a table with 100M rows. I am able update my table like 850 updates / minute. How to speed this up?

I am using following approach:

mysql -uroot < query_file

where query_file contains 1M update queries.

The queries are like:

update table a set col1=1 where col2="something";

Please note, that the value of col2 is different for each query.

What would be the fastest approach to bulk update this mysql table (Innodb)?

Moreover, can I optimize this query like by col2 as a primary key or unique or index or anything else, you can suggest?

UPDATE:

Table has 8 columns.

Right now, the Primary key is a combination of url_hash(16) and domain name(say col 1 and col 6). Though, I am planning to add auto-increment id column as the primary key (col2 in the above example)

Table has 4 BTREE Type index:

  • Index 1 on say col 1 and col 6 <-- primary key
  • Index 2 on say col 1, col 3 and col 4
  • Index 3 on say col 1, col 5
  • Index 4 on say col 4
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4 questions: Do you have an index on col2? Do you have a lot of other indexes? Will those updates change all queries or just a subset? Is the new value of col1 always different from the old value? –  Jannes Feb 10 '12 at 22:08
    
Indexes detail added above. Each update are going to do just one unique row in the table. col1 value can only be 1 or 0. It might be possible that col1's old and new value are same. –  dragosrsupercool Feb 10 '12 at 22:58
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2 Answers 2

The first thing you need to determine about col2 is if it can be a PRIMARY KEY.

Run this query

SELECT COUNT(1),col2 FROM table GROUP BY col2 HAVING COUNT(1) > 1;

If nothing comes back, then col2 can be a UNIQUE KEY. If even one row comes back, then col2 cannot be a UNIQUE KEY. You can create an index on it.

Since this query would take a while without an index, just go ahead and index it

ALTER TABLE table ADD INDEX col2 (col2);

but that might take a very long time.

You may need a temp table to accomplish this:

Step 01) Create a table that will hold the one million col2 values

DROP TABLE IF EXISTS col2values;
CREATE TABLE col2values ENGINE=InnoDB SELECT col2 FROM table WHERE 1=2;
ALTER TABLE col2value ADD PRIMARY KEY (col2);

Step 02) You can load the col2values table with the one million col2 values

Step 03) Index col2

CREATE TABLE table2 LIKE table;
ALTER TABLE table2 ADD INDEX col2 (col2);
INSERT INTO table2 SELECT * FROM table;
DROP TABLE table;
ALTER TABLE table2 RENAME table;

Step 04) Perform update using INNER JOIN

UPDATE col2values A
INNER JOIN table B
USING (col2)
SET B.col1=1;

In the above steps

  • Step 03 needs to be done only once
  • Step 03 is done with 5 lines rather than ALTER TABLE table ADD INDEX col2 (col2); because it would require a full rollback operation should anything go wrong.
  • All other steps are your bulk insert steps going forward

Give it a Try !!!

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Adding an index for col2 will definitely help you a lot. PRIMARY KEY or UNIQUE would be best in your case.

It's usually (always?) better to have a single (auto-increment) numeric column as the primary key. You can make col1+col6 a UNIQUE key instead.

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