Need Advice on Very Low Hit Rate Topic is solved

FAQ, getting help, user experience about PrimoCache
Post Reply
Mingyuan
Level 3
Level 3
Posts: 10
Joined: Mon Jul 26, 2021 7:17 am

Need Advice on Very Low Hit Rate

Post by Mingyuan »

I've been using PrimoCache for over a month and the hit rates are very low. I have 3 Caching Tasks running: a C: drive on which the OS and my "service apps" (apps that start at bootup and keep running as long as the PC is on), cached C: by 8 gig of RAM. The D: drive is a SSD on which all other apps are installed and is cached by 16 gig of RAM. A bunch of HDDs on which I store tons of databases but only access a small portion at a time, cached by 2 gig of RAM and 256 gig L2.

The caching works absolutely awesome on the HDDs, without looking at the numbers I can notice a huge improvement just by using it. However, I only get about 10% hit rate on the D: drive and below 1% on C:. I used all default setting except changing block size to 16KB. Is this what I should get or is there anything I can do to make it better?

Thank you guys in advance!
User avatar
Jaga
Contributor
Contributor
Posts: 692
Joined: Sat Jan 25, 2014 1:11 am

Re: Need Advice on Very Low Hit Rate

Post by Jaga »

Hit Rate simply relies on the same data (blocks) being read multiple times, and there being enough cache space to hold most used blocks. Are you using prefetch at Windows boot? It can help quite a bit to keep hit rate higher.

Hard to say on the database volume, since it also has L2 caching. But the bottom line for hit rate: the more the same data is used, the better the result. I find different apps respond differently as well. Some apps/games cache well and consistently give me 90% or higher. Others just don't like to play nice and sit under 50% all the time. But I don't fault Primocache, since I've been using it going on 8 or so years now and it's done a great job.

Also - it can take time to fully populate the cache(s) so that hitrate finally starts to climb, sometimes just days, other times weeks.

If you want to post some screenshots of config screens it might help to give other tips on what might be changed.
InquiringMind
Level SS
Level SS
Posts: 477
Joined: Wed Oct 06, 2010 11:10 pm

Re: Need Advice on Very Low Hit Rate

Post by InquiringMind »

Mingyuan wrote: Mon Aug 23, 2021 11:29 am The caching works absolutely awesome on the HDDs, without looking at the numbers I can notice a huge improvement just by using it. However, I only get about 10% hit rate on the D: drive and below 1% on C:. I used all default setting except changing block size to 16KB. Is this what I should get or is there anything I can do to make it better?
Windows' own file cache takes precedence over PrimoCache, so it could be that this is dealing with C: and D: (a way to test is to use a utility that can flush the Windows cache such as this, and then seeing if the PrimoCache hit rate improves afterwards).

Unfortunately, there doesn't seem to be an easy way to disable Windows' own file caching (though I'd like to point Romex's programmers at this for a possible workaround) - but if you find this to be the cause, at least you can take the memory used for L1 caching on C: and D: and re-allocate it to your HDDs.
User avatar
Support
Support Team
Support Team
Posts: 3622
Joined: Sun Dec 21, 2008 2:42 am

Re: Need Advice on Very Low Hit Rate

Post by Support »

For L1 cache, enabling Prefetch might help.
Post Reply