Wordpress Misbehaving After Customization

[transfield]

Hi,
I have a Wordpress 4.0.2 site. I engaged a programmer to do some customization to it. He wrote all the php code into the functions.php of my theme. I didn’t realize that this was a bad move as I was new to Wordpress customization & I relied upon him for his ‘expert’ advice.

While the codes are all working fine the side effect of his work is as follows:

1. The site is sluggish
2. It throws up some hidden javascript errors that prevents other Wordpress plugins from functioning
3. WordPress’ admin-ajax.php has been blocked from loading
4. It is loading jquery multiple times from an external google api link
5. I can’t update / change my theme anymore for fear that the functions.php file will no longer work on the new theme
6. The searchability is unstable
7. I dare not upgrade my version of Worpress for fear that something might get messed up

Additional Info
One of the core functions of this Wordpress site is to query an external Mysql database containing approximately 20 million records. Could this be a contributory factor to the sluggishness of the site?

Under such circumstances, what is the best way to maintain all the customization but improve the performance of this site?

Thanks for your advice.

[oddz]

Sounds you like you need to seek out someone more qualified and/or migrate to a new system that is more adequate in handling a database of 20 million records because that beyond certainty is not Wordpress. Maybe I’m not understanding correctly but you have a MySQL database with 20 million rows running on Wordpress. The fact the site even runs is amazing.

[transfield]

Thanks for your advice oddz. The 20 million records are in a separate Mysql database, not the Wordpress Mysql database. Is there a problem with this arrangement?

How about the codes in functions.php. What do I do with them?

Thanks.

[oddz]

I’m not sure because I stay as far away from Wordpress as possible. The whole thing is a dirty mess, scales horribly and ecosystem is plagued with fraud developers who barely know what they are doing. Good luck on resolving your problems.