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vcl_vrt: Skip VCL execution if the client is gone #3998

Merged
merged 4 commits into from
Oct 18, 2023
Merged

vcl_vrt: Skip VCL execution if the client is gone #3998

merged 4 commits into from
Oct 18, 2023

Commits on Oct 17, 2023

  1. vtc: Avoid cycling the barrier in t02014 

    It was particularly hard to follow once we reach client c3.
    @dridi
    dridi committed Oct 17, 2023
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  2. transport: New poll method 

    The goal is for top-level transports to report whether the client is
still present or not.
    @dridi
    dridi committed Oct 17, 2023
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  3. vcl_vrt: Skip VCL execution if the client is gone 

    Once a client is reportedly gone, processing its VCL task(s) is just a
waste of resources. The execution of client-facing VCL is intercepted
and an artificial return(fail) is returned in that scenario.

Thanks to the introduction of the universal return(fail) proper error
handling and resource tear down is already in place, which makes this
change safe modulus unknown bugs. This adds a circuit breaker anywhere
in the client state machine where there is VCL execution.

A new Reset time stamp is logged to convey when a task does not complete
because the client is gone. This is a good complement to the walk away
feature and its original circuit breaker for the waiting list, but this
has not been integrated yet.

While the request is technically failed, it won't increase the vcl_fail
counter, and a new req_reset counter is incremented. This new behavior
is guarded by a new vcl_req_reset feature flag, enabled by default.

Refs varnishcache#3835
Refs 61a15cb
Refs e5efc2c
Refs ba54dc9
Refs 6f50a00
Refs b881699
    @dridi
    dridi committed Oct 17, 2023
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  4. http2_session: Implement transport polling 

    The error check is not performed in a critical section to avoid
contention, at the risk of not seeing the error until the next
transport poll.
    @dridi
    dridi committed Oct 17, 2023
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