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neon/libs
Alex Chi Z. 211e4174d2 fix(pageserver): preempt and retry azure list operation (#9840)
## Problem

close https://github.com/neondatabase/neon/issues/9836

Looking at Azure SDK, the only related issue I can find is
https://github.com/azure/azure-sdk-for-rust/issues/1549. Azure uses
reqwest as the backend, so I assume there's some underlying magic
unknown to us that might have caused the stuck in #9836.

The observation is:
* We didn't get an explicit out of resource HTTP error from Azure.
* The connection simply gets stuck and times out.
* But when we retry after we reach the timeout, it succeeds.

This issue is hard to identify -- maybe something went wrong at the ABS
side, or something wrong with our side. But we know that a retry will
usually succeed if we give up the stuck connection.

Therefore, I propose the fix that we preempt stuck HTTP operation and
actively retry. This would mitigate the problem, while in the long run,
we need to keep an eye on ABS usage and see if we can fully resolve this
problem.

The reasoning of such timeout mechanism: we use a much smaller timeout
than before to preempt, while it is possible that a normal listing
operation would take a longer time than the initial timeout if it
contains a lot of keys. Therefore, after we terminate the connection, we
should double the timeout, so that such requests would eventually
succeed.

## Summary of changes

* Use exponential growth for ABS list timeout.
* Rather than using a fixed timeout, use a timeout that starts small and
grows
* Rather than exposing timeouts to the list_streaming caller as soon as
we see them, only do so after we have retried a few times

Signed-off-by: Alex Chi Z <chi@neon.tech>
2024-11-22 17:50:00 +00:00
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