bert hubert finally blogs

Shopping, pizza, SSHFP

Posted by bert hubert Mon, 03 Apr 2006 20:33:00 GMT

Last week I received an invitation to become a member of a superstore. Due to planning idiocies, large supermarkets aren’t allowed outside of city centers (get this) here in The Netherlands, so you need to be a ‘member’, which is only possible if you have a business. Luckily I have several.

But the odd thing was that I already was a member. But they did send a 20 euro discount voucher! So I went there today to ‘apply’ for membership, and they duly discovered I already was a member. Could I still cash my discount voucher?

Much pondering, calling of supervisors, issuing of stamps later, it was decided I could. 20 euros is no small thing so I immediately splurged lots more on vital stuff like…

Pizza

.. several kinds of ready-made pizza products. Avid readers of this blog will know that I have a worrying addiction to these ancient flat-breads, so why would I try pre-made stuff? Well, I can be stupendously lazy at times, that’s why. I’ve not yet met a good programmer who isn’t lazy, so this is good news.

On to the vital stats. The ‘Nestle’ perishable pizza bottom looks expensive, well made, and even _is_ expensive. When prepared in my pizza oven, it even looks perfect, very thin, very Neapolitan. It tastes likes carton though.

I also tried a smaller no-brand pizza bottom which is thicker and looks less professional, but which tasted a lot better. Nothing compared to my home made dough though.

I bought several bottles of varying kinds of ‘pasta sauce’ and it turns out they are all fine. My new pizzas don’t have a lot of sauce on them, I find that even the very cheap ready-made sauce is very good.

All in all, a worthwhile experience.

PowerDNS

A day that didn’t really go anywhere. Spent quite some time fighting different-endian PCAP files. PowerDNS contains technology to replay recorded DNS streams for verification and analysis purposes, for which it needs to be able to parse tcpdump files. It turns out these come in both big- and little-endian flavours.

Furthermore, Solaris has a 2*64-bit struct timeval, whereas pcap files use regular 32-bit time_t values. So I had to abstract that all out. Didn’t commit it to SVN yet as part of the code doesn’t work yet.

Peter Zijlstra previously educated me on the use of ‘clock algorithms’ for cache pruning. PowerDNS currently prunes based on the TTL of records, which is probably not the best thing to do. A long-lived record has no need to outstay a shorter lived one if it is never queried.

My local sources now put a record in the back of a linked list every time it is accessed or created (many thanks to Joaquín Mª López Muñoz for explaining how this works). When we want to prune, we start with the least used records, which are at the beginning.

When the recursor tries to find a record in the cache and finds it to be expired, it can simply ignore it. It will be refreshed soon anyhow.

It would appear this could speed up PowerDNS a lot, and also enable us to limit ourselves to a fixed amount of memory used (see below).

Also, implemented RFC 4255, SSHFP, which took all of 30 minutes, counting the implementation of hex-encoded records. Without that infrastructure, it would’ve taken 3 minutes.

This does not do anything yet - the recursor does not need to know about SSHFP and the authoritative nameserver doesn’t use the innovative ‘MOADNSParser’ yet. I’ll probably change that before 2.9.21.

Unix

I also spent some time trying to get the linux implementation of getrusage fill out the ‘integral’ memory fields. Turns out no OS I have access to uses these fields as their definition has traditionally been crap. SuSv3 also doesn’t mention these fields at all. So that was some lost effort. It appears you’ll have to do something different on each unix to discover real memory usage.

In working on this, I managed to get UML compiled and working without too much work, which is a first. The UML defconfig is not very good though, will send Jeff Dike a patch.

I did discover mallinfo(2) today, which is present in all unixes it appears, and provides information on the memory allocation subsystem. The numbers nedmalloc output here appear to be bogus though.