For info, I have a hard limit of 5 MB I/O per second. It’s not a lot but as my sites are optimized, I never went above 3MB per second before enabling redis plugin.
Redis requires additional compute and memory to run, I’d suggest upgrading your account. Typically people run Redis on 2GB servers. it can be tight when only 1GB RAM is available.
I’ve never heard about I/O per sec as a limiting metric, what host are you using.
I am with sawebhosts.co.za. Definitely something weird is going on. Tried many many many times. In the end, it always results in high i/o.
I did a LOT of testing and found that this happens when turning it on for any two sites on one hosting package. I have a domain and subdomain; no matter what I do, it works with either as long as only one uses redis at a time. Specifying a DB or prefix does nothing to change this. I suspect it’s because the server uses virtualization.
So, the only option is to select which site must be accelerated and turn redis on there. I hope this helps anyone else on shared hosting that uses virtualization.
@tillkruess thanks for all the support!!
Thanks for the report. TBH it’s the first time I’ve heard that someone is restricted by I/O, typically people run a VPS with >2GB of memory.
Some sites use a lot more object cache keys and will thus transfer a lot more data. You can see the average cache size per page in the metrics under “Bytes”.
@tillkruess, it’s not that it has high I/O. The hosting runs on cagefs virtualization, and cannot handle a domain and subdomain both using redis on that virtualized instance. It becomes screwy, and starts creating excessively high i/o.
With two sites, and only the one site on redis, the i/o is an average 400kb per second. But as soon as I switch on redis for both sites, the i/o is maxed out. I also start receiving random fatal WordPress errors, which goes away when I turn redis off an only let it run on one site at a time. And no, they are not sharing the same database. So, looks like cagefs cannot support redis for two sites on one virtualized instance.
Update: It’s working on both.
There are two php versions available on a virtualized instance, alt-php (provided by CloudLinux) & ea-php (shipped by cPanel).
I was using ea-php which cannot work with two redis on one instance. I switched to alt-php and everything is happy happy happy!
