Hi, I run into this issue today many times :
"Link to database cannot be established: SQLSTATE[HY000] [1135] Can't create a new thread (errno 11 "Resource temporarily unavailable"); if you are not out of available memory, you can consult the manual for a possible OS-dependent bug"
This does not seem to happen to any specified page, it happens to both front-end and back-end pages or tabs. The resource seems to be temporarily unavailable or Mysql out of memory for a sec but if I refresh the page right after it will load no problem.
I tried to disable non PrestaShop modules and disable all overrides in debug mode but it still occurs. I also contacted my hosting provider, they don't think it's a server side issue and everything looks OK on their side. I did a bit googling and found this happen to someone else before here and some similar issue with Mysql . Some suggested it will fix it by change PHP to 5.3 but no luck in my case, I am using PHP7 by the way.
There is also suggest of changing this /etc/security/limits.conf will work but I can't connect to my host via SSH for some reason. I will keep on trying this next.
If anyone knows what's happening or seen it before please let me know.
Any help would be much appreciated.