proxy_cache_lock for content revalidation

[Maksim Yevmenkin]

hello,

> > it seems that the proxy_cache_lock directive operates only for cache
> > misses (new content). while this behavior is documented, i am curious
> > about the reasoning behind it. there are scenarios where
> > proxy_cache_lock could be very beneficial for content revalidation.
> > what are the community's thoughts on this?
>
> The generic idea is that "proxy_cache_use_stale updating;" is a
> better option for existing cache items.  As such, current
> implementation of proxy_cache_lock doesn't try to handle existing
> cache items to reduce complexity.

right. there are instances where serving outdated content is not
permissible, yet overwhelming the upstream servers with a flood of
requests is highly undesirable. this situation occurs quite
frequently.

> Just in case, at least one previous attempt to extend
> proxy_cache_lock to work with existing cache items can be found
> here:
>
> https://mailman.nginx.org/pipermail/nginx-devel/2018-December/011710.html

thank you! it seems the original post mentioned this exact issue. it
also seems that the patch was removed. i am curious if it would be
possible to restore the patch.

thanks,
max