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Simple bash shell script for running batch MySQL jobs

By Barrett Griffith · Tuesday, October 16, 2012

Tags: shell, mysql

The other day I needed to run a simple mysql job to backup and delete some database records on a live server. Being a live server, it is important to make sure you aren't asking the database to take on jobs that could potentially lock it up. Better to run a batch job. Running a batch is simple. You can call it right from the mysql console with:

source [path_to]/[the_batch_script].sql

But what if there are millions of records that need deleting? Bash shell script to the rescue.

Here is the idea of the SQL job that needed to get run a few times:

START TRANSACTION;

/* Find what you want to delete and put a LIMIT on your batch size */
CREATE TEMPORARY TABLE records_to_delete_temp SELECT id from `records` where ..... limit 1000;

/* Creating backup table to archive spam orders */
CREATE TABLE IF NOT EXISTS `records_backup` LIKE `records`;
INSERT INTO `records_backup` SELECT * from `records` where id in (select id from `records_to_delete_temp`);

/* Delete Dependents - If your records have foreign key dependencies, delete them first */
DELETE FROM `dependent_1` where record_id in (select id from `records_to_delete_temp`);
DELETE FROM `dependent_2` where record_id in (select id from `records_to_delete_temp`);

/* Delete the records */
DELETE FROM `records` where id in (select id from `records_to_delete_temp`);

/* Return count of remaining records - the where clause should be the same as the original select for the records to delete */
SELECT COUNT(*) from `records` where .... ;

COMMIT ;

Note:

SELECT COUNT(*)

This will return the remaining record count to the shell script.

And the shell script...

ret=$(mysql -u [user] -p[password] --skip-column-names [database_name]  < [the_batch_script].sql)

while [ $ret -gt 0 ]
do
  echo "rows left: $ret"
  sleep 3
  ret=$(mysql -u [user] -p[password] --skip-column-names [database_name]  < [the_batch_script].sql)
done

Notes:

--skip-column-names

This is the little nugget that gives you clean output from the mysql script. Without --skip-column-names you will have to get more creative with parsing the returned table.

-p[password]

Just a friendly reminder, no space after the -p option.

Should you really be running batches to remove millions of records from a live server with a shell script?

Just because you can doesn't mean you should. Before pulling the trigger, back up, consider what could go wrong, have a plan in place to address the possible failure.

Find something fun for your hands to do while bash takes care of running the jobs. At the least, cross your fingers!

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