Comment by devin
2 days ago
From a practical standpoint, isn't it usually the case that there are retention periods for traces given how numerous they can be?
I bring this up because this article starts with "I asked Claude", but it doesn't explore the the length of time you're generating IDs over at all, which is an important aspect to consider when selecting size.
Yes. The original Dapper used 64 bit trace ids and collisions were rarely a problem.
If you don't drop any spans from a trace, you can completely disambiguate a collision since the trace will have two distinct root spans. If you are missing spans, you might have a break in the parent-child links.
Even with infinite retention, your analysis will bucket by time somehow, so a collision might have no effect if the collision doesn't happen at a proximate time. If you are manually looking at traces, it will be very obvious there is a collision unless they happen at the same time.
Also, birthday paradox only expresses probability that there is a collision somewhere, but if you are filtering or looking at single spans, then the probabiliy that you actually see a collision is greatly reduced.
I think for basically all systems, an additional 64-bits has insignificant additional cost, so you may as well prevent collisions, but I think it could be a reasonable tradeoff if it mattered.
nod Adding this to my growing list of "things experienced engineers would discuss which is conspicuously missing in this case"
The future is going to be filled with "best practices" trendslop decision-making.