# workers-discussions
- d
dave
03/08/2023, 9:26 PMhttps://developers.cloudflare.com/r2/data-access/s3-api/presigned-urls/#presigned-url-alternative-with-workers:~:text=%22If%2DUnmodified%2DSince%22%3A%20%22Tue%2C%2028%20Sep%202021%2016%3A00%3A00%20GMT%22%2C How does the
header actually enforce anything? Can't clients just write a file multiple times with the same header?If-Unmodified-Since - k
kian
03/08/2023, 9:33 PMPutObject would reject it with a 304 - d
dave
03/08/2023, 9:56 PMhuh interesting - t
Tom Sherman
03/08/2023, 11:14 PMIs it possible to trace a worker? I'm mostly interested in finding out how long sub-requests take - t
Tom Sherman
03/08/2023, 11:14 PMI'm assuming the answer is no as I can't find any info on the subject 😅 - u
Unsmart | Tech debt
03/08/2023, 11:15 PMyou can trace it yourself yes nothing cloudflare provides out of the box automatically at the moment - k
kian
03/08/2023, 11:15 PMyou'd just be date.nowing yourself - k
kian
03/08/2023, 11:16 PMall timers in Workers have Spectre mitigations so it won't be exact, but enough to show trends I guess - t
Tom Sherman
03/08/2023, 11:22 PMShould be accurate enough to show sub-request flame graph right? - t
Tom Sherman
03/08/2023, 11:23 PMI guess I'd have to add some logging around subrequests (somehow), and then use a worker to transform the logs into datadog traces - h
HardAtWork
03/08/2023, 11:36 PMCan you DevTool it? - t
Tom Sherman
03/08/2023, 11:37 PMHmmmm, I haven't used the devtools much. Do they show subrequests in the network tab? Would be super cool - t
Tom Sherman
03/08/2023, 11:37 PMWould help with local debugging for sure, still need production observability tho - h
HardAtWork
03/08/2023, 11:38 PMNo idea. I always used Firefox, which seemed to be a little buggy when I tested it - h
HardAtWork
03/08/2023, 11:38 PMYou tried a logger like Toucan? - t
Tom Sherman
03/08/2023, 11:39 PMWe don't use sentry - h
HardAtWork
03/08/2023, 11:39 PMOr Honeycomb - t
Tom Sherman
03/08/2023, 11:40 PMIt's all datadog here 😅 - t
Tom Sherman
03/08/2023, 11:40 PMI guess I could look at how toucan works, if they are doing tracing - j
James
03/08/2023, 11:43 PMWalshy has a pretty cool Workers tracing library if you wanted to take a look at that, too: https://github.com/BlobDevelopment/workers-tracing - t
Tom Sherman
03/08/2023, 11:47 PMOk yep this is exactly the kind of thing I was after, thanks folks! - t
Tom Sherman
03/08/2023, 11:48 PMI really think workers are gonna need a tracing story for measuring CPU time at some point tho with more people shipping full apps to workers. No idea how they can pull it off tho 😅 - d
Deleted User
03/09/2023, 1:18 AMIf a worker returns a fetched item, how long is that item cached? - k
kian
03/09/2023, 1:19 AMBy default? 0 - k
kian
03/09/2023, 1:19 AMWorkers run before the cache so you'd need to place it into the Cache API and retrieve it upon request - k
kian
03/09/2023, 1:19 AMWorkers are always invoked, you can't use the cache to prevent it - d
Deleted User
03/09/2023, 1:19 AMThat's what I figured - d
Deleted User
03/09/2023, 1:19 AMBut it's not fetching an updated page