| BBlack added a comment. |
In T179156#3719928, @daniel wrote:In any case, this would consume front-edge client connections, but wouldn't trigger anything deeper into the stackThat's assuming varnish always caches the entire request, and never "streams" to the backend, even for file uploads. When discussing this with @hoo he told me that this should be the case - but is it? That would make it easy to exhaust RAM on the varnish boxes, no?
Maybe? I haven't really delved deeply into this angle yet, because it seems less-likely to be the cause of the current issues. We have an obvious case of normal slow chunked uploads of large files to commons to look at for examples to observe, though. Because they're POST they'd be handled as an immediate pass through the varnish layers, so I don't think this would cause what we're looking at now. GETs with request-bodies that were slowly-chunked-out might be different, I don't know yet.
this is definitely on the receiving end of responses from the applayer.So a slow-request-log would help?
Yes. We've gathered those manually in specific cases so far. Aggregating them across the varnishes to somewhere central all the time will require some significant work I think. Right now I'm more-worried about the fact that, since varnish doesn't log a transaction at all until the transaction is complete, without overall transaction timeouts on the backend connections there are cases that would slip through all possible logging (if they stayed open virtually-indefinitely and sent data often enough to evade the between_bytes_timeout check).
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