Capacity & RAM

Re: Capacity & RAM

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Lotta questions in this thread. Rather than respond to them with a flurry of posts to the list, let me address them all here.

At 9:30 AM -0600 11/5/99, Steve Dannaway wrote:
>This addition will take my DNS to almost 2.5 millions hits per month.
>So after much ado, the question is: Can a 7500 handle this type of load?
>If not, what would be the minimum recommended machine that you would
>use.

That's nothing.
2.5M hits/mo = ~80K hits/day = ~3.5K hits/hr = ~1 hit/sec.

Even if your traffic varies by up to a factor of 10 from this average during the course of the day, a Mac IIci could probably handle this without trouble. (For those who don't remember the IIci, it's a 25MHz 68030 with a really nice case design.) Any PowerPC should be able to go to sleep under this kind of load.

At 11:23 AM -0500 11/5/99, andrew kagan wrote:
>Run, don't walk, to v. 2.2.1 before you do anything else!

Agreed. We fixed some bugs and added a nice log window between these two versions.

At 10:16 AM -0600 11/5/99, Jerry Pasker-Systems Admin. wrote:
>I've been running
>my primary on a 6220 CD, (75Mhz 603, and the slowest PowerMac ever made)
>with 24MB of RAM (12 allocated to QDNS Pro 2.2.1) and have found that under
>a pretty good load (3-10 quirries per seccond) less RAM is better than more
>RAM. I'm only assuming that it's faster to search 1.5MB of cached records,
>and then resolve a name using an external server(s) than it is to sort
>through 11.5MB of cached records.
>
>I'm sure there has to be a guideline to setting RAM on different speeds of
>machines. Or is more allways better? Can anyone clarify this?

In theory, more RAM is better, up to the point where the available RAM is not all used. Beyond that, more RAM is simply unused. You can check the free memory reading in the status window.

However, that is a slow machine.

Keep in mind that, no matter how fast the machine, there will be a point where more RAM will slow it down. This is true of any type of system that stores data in a table in RAM. Furthermore, when resolving outside queries, QuickDNS Pro can also find the same answers by the usual resolution routine, so the point of inefficiency can be even lower, especially for slow machines.

It sounds like you've empirically found your answer.

>Here's a good question for the DNS gods..... why is a zone transfer faster
>from a 25Mhz Performa 600 (2MB allocated to QDNS Pro) (250+ records,
>500ms) than the 75Mhz Performa 6220 (same 250+ records 2200+ ms)

I can only guess.

The 68K processor family is pretty well designed for a CISC architecture. The 603 (not the 603e) kinda sucks as a RISC processor. When you look at the numbers in the Apple Spec database, it looks like the 6220 should outperform the 630 about 2:1. Anyone who's ever used both will probably tell you that it's really the other way 'round.

Keep in mind that, although the Performa has a faster memory bus, in reality the RAM is running at 16MHz (60 ns) or slower on both systems. QuickDNS Pro is very much affected by RAM speed.

BTW: According the the Apple Spec database, the 600 is a 32 MHz '030 with a 16 MHz bus.

>What are QDNS Pro's upper limits in terms of resolving DNS quiires?

That depends on the machine and the OS, of course. The faster the machine & OS, the higher the capacity.

At 11:41 AM -0500 11/5/99, andrew kagan wrote:
>I think it has more to do with disk cache, bus speed, processor activity,
>process priority and a zillion other issues than the actual ram allocated to
>QDNS...unless you've throttled the ram allocation under the minimum.

Disk cache is totally unrelated, except as it affects other processes (including virtual memory, if you're using it). QuickDNS Pro holds *everything* in memory.

That isn't quite true, actually: QuickDNS does scan its Primary Data folder once per minute, so it spends quite a bit of time waiting for the OS to tell it the modification times of the files therein. Luckily, as a heavily multithreaded application, it spends that time serving.

>What do queries have to do with zone transfers? Any upper limits will be
>determined by the hardware, not the software, at this point...unless you're
>running an authoritative root server.

A zone transfer is sent as a series of query responses, specially formatted. Each record is sent individually, if you can believe it. And software does indeed affect upper limits - just compare MacDNS to QuickDNS Pro.

At 9:47 AM -0800 11/5/99, eric@micromaniac.com wrote:
>I'm curious...what are recommended memory settings for QuickDNS Pro 2.2.1?

When you first start QuickDNS Pro, look at the free memory reading in the status window. It should be at least 1 MB (1048576), in order to have some room to cache outside entries. Beyond that, see the discussion above regarding more and less memory on the Performa 6220.

Any additional memory you give it translates directly to more memory for caching.

>I host about 10 domains (plus their CNAME stuff), and our LAN and dial-ups
>also our DNS (never more than 5 users at a time). A few domains have good
>traffic from time to time, but otherwise the overall traffic is low to
>moderate.
>
>The suggested size is 2278K, and I've never seen a delay (except for the
>first external look-ups outside of my DNS after restarts, which is probably
>normal). I currently have them at 4M each. I have plenty of RAM to crank
>them up ten-fold, but I doubt we'd ever "fill them up" since we restart our
>servers once a week.

When the first query for an outside name comes in, QuickDNS uses its list of root servers (the hint list) to query a root server for a new list of root servers. This way, any changes in the roots from its internal list are noticed before it starts resolving any outside queries.

The root servers have been very busy lately; many of them are becoming unuseable during peak load times. It's kind of a problem.

If you have a decently fast server, you can load QDNS up on memory until it never runs out of free memory (as indicated in the status window).

At 12:26 PM -0500 11/5/99, Kurt Anderson wrote:
>We have a 603e/200 MacOS 8.6 with 80megs of RAM, 40 goes to QuickDNS Pro
>2.2.1 and I've found when the available memory goes below 25 megs things
>get dicey (crashed/hung in the past) so I reboot the server when it hits
>this watermark.
>
>Am I giving it too much RAM? The box only does DNS. It's doing primary
>for about 2K+ domains.

Please contact support@menandmice.com so we can help you determine the cause of the crashing. It shouldn't have any trouble going below 25MB of free memory.

Until then, try turning down its memory allocation using the 1MB initially free algorithm described above. Then when you're satisfied that it's stable, increase the memory allocation by a few MB at a time, so that you get good speed (and good caching) without sacrificing stability.
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Chris Buxton cbuxton@menandmice.com
Men & Mice http://www.menandmice.com
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