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From Andrew Mains <>
Subject Tracing a chain of iterators -- htrace 2.04
Date Tue, 18 Aug 2015 22:03:45 GMT
Hi all,

This is really more of a "user" question than a "dev" question, but I'm 
posting here since I was unable to find a user list for the project; 
hope that's alright.

I was hoping to get some input on the best way to trace execution 
through a chain of iterators. Specifically, we have a database-like 
application which pipes data through multiple iterators, performing some 
transformation at each step. We'd like insight into how long each step 
is taking in total for a particular request. That is, for a chain of 
iterators iter_1... iter_i, we want the total time spent in each iter_i 
for that request.

The naive implementation would be to start a span in each call to next, 
but that's far too fine grained, given that we'd be starting a new span 
for each row. What we'd really want, is to aggregate the time spent in 
each call to next for each iterator, and then send the spans at the end. 
This would require implementing a new span subclass, which is a bit 
tricky to integrate at the moment (since it prevents us from using the 
static helpers in Trace).

Any thoughts on the best way to approach this issue? Is there something 
I'm missing, or some way that we can reframe the problem such that it 
makes sense with what's currently in htrace?

Let me know if there's anything that's unclear, or any further info I 
can provide about our use case.

Thanks for the help!


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