ccan/mem’s memeqzero iteration

On Thursday I was writing some code, and I wanted to test if an array was all zero.  First I checked if ccan/mem had anything, in case I missed it, then jumped on IRC to ask the author (and overall CCAN co-maintainer) David Gibson about it. We bikeshedded around names: memallzero? memiszero? memeqz? memeqzero() won …

Broadband Speeds, New Data

Thanks to edmundedgar on reddit I have some more accurate data to update my previous bandwidth growth estimation post: OFCOM UK, who released their November 2014 report on average broadband speeds.  Whereas Akamai numbers could be lowered by the increase in mobile connections, this directly measures actual broadband speeds. Extracting the figures gives: Average download …

The Bitcoin Blocksize: A Summary

There’s a significant debate going on at the moment in the Bitcoin world; there’s a great deal of information and misinformation, and it’s hard to find a cogent summary in one place.  This post is my attempt, though I already know that it will cause me even more trouble than that time I foolishly entitled …

The Megatransaction: Why Does It Take 25 Seconds?

Last night f2pool mined a 1MB block containing a single 1MB transaction.  This scooped up some of the spam which has been going to various weakly-passworded “brainwallets”, gaining them 0.5569 bitcoins (on top of the normal 25 BTC subsidy).  You can see the megatransaction on blockchain.info. It was widely reported to take about 25 seconds …

Bitcoin Core CPU Usage With Larger Blocks

Since I was creating large blocks (41662 transactions), I added a little code to time how long they take once received (on my laptop, which is only an i3). The obvious place to look is CheckBlock: a simple 1MB block takes a consistent 10 milliseconds to validate, and an 8MB block took 79 to 80 …

Wrapper for running perf on part of a program.

Linux’s perf competes with early git for title of least-friendly Linux tool.  Because it’s tied to kernel versions, and the interfaces changes fairly randomly, you can never figure out how to use the version you need to use (hint: always use -g). But when it works, it’s very useful.  Recently I wanted to figure out …

Hashing Speed: SHA256 vs Murmur3

So I did some IBLT research (as posted to bitcoin-dev ) and I lazily used SHA256 to create both the temporary 48-bit txids, and from them to create a 16-bit index offset.  Each node has to produce these for every bitcoin transaction ID it knows about (ie. its entire mempool), which is normally less than …

Mining on a Home DSL connection: latency for 1MB and 8MB blocks

I like data.  So when Patrick Strateman handed me a hacky patch for a new testnet with a 100MB block limit, I went to get some.  I added 7 digital ocean nodes, another hacky patch to prevent sendrawtransaction from broadcasting, and a quick utility to create massive chains of transactions/ My home DSL connection is …

What Transactions Get Crowded Out If Blocks Fill?

What happens if bitcoin blocks fill?  Miners choose transactions with the highest fees, so low fee transactions get left behind.  Let’s look at what makes up blocks today, to try to figure out which transactions will get “crowded out” at various thresholds. Some assumptions need to be made here: we can’t automatically tell the difference …