Too much memory use is causing mySQL to crash

Hi Team,

Please could you help me with this issue that my host and I are struggling with?

I used to host my blog https://cadsetterout.com/ on a shared server. I was experiencing a lot of 505 errors.

Checking the logs I could see that I was the subject of CPU throttling, because my blog was using too much memory.

My host recommended moving to a VPS, which I have now done – hoping that the shear amount of traffic to my blog was causing the problem ?? (1000 – 1500 hits per day)

Since I moved to a VPS I’ve been having a different problem ‘Cannot connect with database error’.

My host has identified (by logging in with Putty) that a couple of scripts are being called that using too much memory to pull data from mySQL. This causes Ommkiller to shut down the thing using the most memory – mySQL, which causes the database error…

(apologies if my technical language isn’t quite correct – I hope you get the gist)

They showed my how to log in with Putty. I can see that (almost) every time I click on a link on my site a script is called that uses 4-8m of memory. I’m guessing that if too many people are on the site at the same time, the scripts are being called too often causing mySQL to crash?

So – we’ve identified that something has been causing this problem for some time, both on a shared server and on a VPS. My site is 6 years old, so who knows what sort of crud could be blocking the system!

Do you have any tips on how I can diagnose which scripts are pulling too much memory and causing the error?

So far I have tried:
Upping the PHP memory to 256m – 64m for any one script
Using sucuri to slow down wordpress Heartbeat
Blocking Cron jobs, and setting up a once a day Cron schedule
Getting rid of as many plugins as possible.
Turning off as many jetpack options as possible.
Increasing the amount of time between scans for Succuri and Wordfence

I am using WP-Total cache and MaxCDN

Thanks in advance for any clues that you can give me which would allow me to progress!