In dump (and ufsdump, and other close cousins) you can specify thefilesystem that you want to dump in two ways: by the name of itsmountpoint, or by the name of the (raw) device that it's on. One ofmy little twitches is that I always specify thefilesystem to dump by its mountpoint. Like a lot of my little twitches,this has a history behind it.

The problem is that at least some old versions of dump were perfectlywilling to write their output to

This week, we:

• got 15,790 messages from 280 different IP addresses.
• handled 23,657 sessions from 1,340 different IP addresses.
• received 248,408 connections from at least 73,118 different IPaddresses.
• hit a highwater of 17 connections being checked at once.

Volume is up again from last week ,although the number of different IPs is down slightly.

I have an embarrassing confession: my home Internet connection is stilla dialup 28.8Kbps PPP link. (Back when I first set it up, this was onlyslightly behind the times, as 33.3Kbps modems had just come out.)

For a long time this was fine, because all I really did with it wastext-based stuff, mostly sshing to my machines at the university; whileI did do some web surfing, pretty much all of the sites I visitedregularly were

Recently, nothings askedan interesting question in a comment here :

[...] why, under the hood, deep down, is something like memcachednecessary? Why isn't the SQL server's cache as effective?

I think that one of the reasons for this is that highly aggressivecaching in an SQL server is much harder than it looks.

In database servers, caches have to be transparent ;non-transparent caches would implicitly break ACID guarantees. Now contemplate theproblem of completely correct cache invalidation that

One of the divisions in caching is between what I will call transparentand non-transparent caches. Transparent caches are ones where the onlything you are supposed to notice is faster speed; non-transparent cachesrequire you to manage them explicitly, especially cache invalidation.Operating system disk caches are an example of transparent caches, atleast in theory.

(At some level every cache is non-transparent, because it has to bemanaged by someone's code. So this is just a question of how a cache

It's not that complex software systems are inherently fragile for theusual reason, because they have more places and pieces to go wrongthan simple systems do; unlike physical machines, computer softwarehas no mechanical wear and thus doesn't just break on its own (barringintrinsic flaws). Living in a digital world, computer software thatworks keeps working forever until something changes.

The real problem with complex systems is that it's very hard for peopleto keep track of all of the interrelationships, and thus

Using DHCP to assign IP addresses is pretty popular in environments withlots of machines. You'd think that student labs, full of generic machines,would thus be a great environment for DHCP, but actually I disagree; Ibelieve that (normal) DHCP is not a great match for a lab environment.

The problem with DHCP is that it ties the IP address to the wrongthing. In a lab environment you don't want a machine's IP addressto be tied to its hardware; you want

In the spirit of previous cleverness ,here's a simple new technique:

Have your web spider make up random Referer headers.

This wasn't Referer spamming, since the websites in the Referer headerswere completely random URLs, apparently drawn from legitimate sitesaround the Internet (often repeated). Nor were the websites ones thatactually linked to us, or had any relationship to the URLs that werebeing crawled.

Even in low volume this is a sure-fire ticket to our kernel level IPfilters, since it

Textareas are one of those treacherous areas of web programming, becauseit is really easy to get them 95% right and then never notice thatyou've fumbled the remaining 5%. The problem area is textareas withinitial content, for example blog comment previews ;what almost completely works is to just put the raw content into thetextarea in your HTML. This approach makes intuitive sense and evenworks fine if you test by throwing markup in, like '

this is atest

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