Do not use BLOB in JobsDB and PilotAgentsDB tables

[fstagni]

@TaykYoku has debugged this further and got to the bottom of it on slack: https://lhcbdirac.slack.com/archives/C3AGWCA8J/p1625147097062700

In summary, the JobParameters table is using BLOB for the value when it should be using a text type.

Originally posted by @chrisburr in #5246 (comment)

[fstagni]

Self reminder: there are several BLOB and MEDIUMBLOB (mis)used instead of TEXT or VARCHAR, especially in JobDB and PilotAgentsDB. The change should be tested on a DB clone first.

[fstagni]

For reference, changes to be tested:

use JobDB;
ALTER TABLE `JobJDLs` MODIFY COLUMN `JDL` MEDIUMTEXT, MODIFY COLUMN `JobRequirements` TEXT, MODIFY COLUMN `OriginalJDL` MEDIUMTEXT;
ALTER TABLE `JobParameters` MODIFY COLUMN `Value` TEXT;
ALTER TABLE `OptimizerParameters` MODIFY COLUMN `Value` MEDIUMTEXT;
ALTER TABLE `AtticJobParameters` MODIFY COLUMN `Value` TEXT;
ALTER TABLE `SiteMask` MODIFY COLUMN `Comment` TEXT;
ALTER TABLE `SiteMaskLogging` MODIFY COLUMN `Comment` TEXT;
ALTER TABLE `HeartBeatLoggingInfo` MODIFY COLUMN `Value` TEXT;
use PilotAgentsDB;
ALTER TABLE `PilotAgents` MODIFY COLUMN `GridRequirements` TEXT;
ALTER TABLE `PilotOutput` MODIFY COLUMN `StdOutput` MEDIUMTEXT, MODIFY COLUMN `StdError` MEDIUMTEXT;

[chrisburr]

I don't know how MySQL handles this internally but can this be made faster by doing it with a single ALTER TABLE command?

[fstagni]

IIUC you can alter only one table at a time.