PHP MySQL - Update 6.5m rows performance issues - php

Question

I am working with a MySQL table and I need to increment a value in one column for each row, of which there are over 6.5m.
The col type is varchar and can contain an integer or a string (i.e. +1). The table type is MyISAM.
I have attempted this with PHP:
$adjust_by = 1;
foreach ($options as $option) {
$original_turnaround = $option['turnaround'];
$adjusted_turnaround = $option['turnaround'];
if (preg_match('/\+/i', $original_turnaround)) {
$tmp = intval($original_turnaround);
$tmp += $adjust_by;
$adjusted_turnaround = '+'.$tmp;
} else {
$adjusted_turnaround += $adjust_by;
}
if (!array_key_exists($option['optionid'], $adjusted)) {
$adjusted[$option['optionid']] = array();
}
$adjusted[$option['optionid']][] = array(
'original_turn' => $original_turnaround,
'adjusted_turn' => $adjusted_turnaround
);
}//end fe options
//update turnarounds:
if (!empty($adjusted)) {
foreach ($adjusted as $opt_id => $turnarounds) {
foreach ($turnarounds as $turn) {
$update = "UPDATE options SET turnaround = '".$turn['adjusted_turn']."' WHERE optionid = '".$opt_id."' and turnaround = '".$turn['original_turn']."'";
run_query($update);
}
}
}
For obvious reasons there are serious performance issues with this approach. Running this in my local dev environment leads to numerous errors and eventually the server crashing.
Another thing I need to consider is when this is run in a production environment. This is for an ecommerce store, and I cannot have a huge update like this lock the database or cause any other issues.
One possible solution I have found is this: Fastest way to update 120 Million records
But creating another table comes with it's own issues. The codebase is not in a good state, similar queries are run on this table in loads of places so I would have to modify a large number of queries and files to make this approach work.
What are my options (if there are any)?

Answer 1

You can do this task with SQL.
With CAST you can convert a string into integer.
With IF and SUBSTR you can check if string contains +.
With CONCAT you will add (merge a two values into one string) + to your calculated result (if it will be necessary).
Just try this SQL:
"UPDATE `options` SET `turnaround` = CONCAT(IF(SUBSTR(`turnaround`, 1, 1) = '+', '+', ''), CAST(`turnaround` AS SIGNED) + " + $adjust_by + ") WHERE 1";

Answer 2

can't you just say
UPDATE whatevertable SET whatever = whatever + 1?
Try it and see, I'm pretty sure it will work!
EDIT: You have strings OR integers? Your DB design is flawed, this probably won't work, but would have been the correct answer had your DB design been more strict.

Answer 3

You probably don't have, but need, this 'composite' index (in either order):
INDEX(optionid, turnaround)
Please provide SHOW CREATE TABLE.
Another, slight, performance boost is to explicitly LOCK TABLE WRITE before that update loop. And UNLOCK afterwards. Caution: This only applies to MyISAM.
You would be much better off with InnoDB.