Upgrading to Varnish 6.4.0

Upgrading to Varnish 6.4 from 6.3 should not require any changes to VCL.

This document contains information about other relevant aspects which should be considered when upgrading.

varnishd

  • The hash algorithm of the hash director was changed, so backend selection will change once only when upgrading.

    Users of the hash director are advised to consider using the shard director instead, which, amongst other advantages, offers more stable backend selection through consistent hashing.

  • We fixed a case where send_timeout had no effect when streaming from a backend fetch.

    Users with long running backend fetches should watch out of increases connection close rates and consider increasing send_timeout appropriately.

    The timeout can also be set per connection from vcl as sess.send_timeout.

Statistics

  • The MAIN.sess_drop counter is gone. It should be removed from any statistics gathering tools, if present
  • Added rx_close_idle counter for separate accounting when timeout_idle is reached. Also, send_timeout is no longer reported as "remote closed".

vsl/logs

  • The Process timestamp for vcl_synth {} was wrongly issued before the VCL subroutine, now it gets emitted after VCL returns for consistency with vcl_deliver {}.

    Users of this timestamp should be aware that it now includes vcl_synth {} processing time and appears at a different position.

  • A Notice VSL tag has been added

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