Intermittently very slow downloads from Legacy Survey fits-cutout service

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Yongmin Yoon

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Apr 13, 2026, 11:10:32 AMApr 13

to DECam Legacy Survey

Hello,

I am writing to report an intermittent download issue with the Legacy Surveys FITS cutout service.

I am downloading the Legacy Surveys FITS cutout images using wget.

For some requests, downloads proceed normally at a few MB/s and finish within seconds. However, for other requests of similar size, the transfer rate drops to only a few tens of KB/s, and the download can take 20-30 minutes or stall until the connection is closed. When wget retries the same URL, the retry often becomes fast again and completes at a few MB/s.

This behavior was not present a few months ago. At that time, downloads were generally smooth and stable.

I have reproduced the issue from multiple networks, including both my lab network and my home network, so it does not appear to be limited to a single local connection.

Because of this issue, I am currently having difficulty downloading the full set of images I need for my work.

If there is a recommended way to access these cutouts more reliably, I would appreciate your guidance.

Thanks in advance.

Yongmin Yoon

Dustin Lang

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Apr 13, 2026, 6:25:28 PMApr 13

to Yongmin Yoon, DECam Legacy Survey

Hi,

Nothing has changed with the code - I think we just have a lot of people trying to do bulk downloads. Attached is a plot of the response time - you can see how much variation there is.

I doubled the number of worker services. Maybe that will help a bit.

cheers,

dustin

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