Varnish VMods for Version 6.1?

Dridi Boukelmoune dridi at
Mon Sep 24 12:14:50 UTC 2018

On Fri, Sep 21, 2018 at 1:50 PM Winkelmann, Thomas (RADIO TELE FFH -
Online) <t.winkelmann at> wrote:
> I again did some testing by settings the params to
> -p thread_pools=4
> -p thread_pool_min=2000
> -p thread_pool_max=5000
> -p thread_pool_reserve=95

Please note that min/max/reserve is per pool.

> The document says that thread_pool_reserve is a value from 0 to 95. It's working fine on one of our two servers which have less load (300 req/s) than the primaray one (> 800req/s).

You really need to read the full description for this one:

    Default is 0 to auto-tune (currently 5% of thread_pool_min).
    Minimum is 1 otherwise, maximum is 95% of thread_pool_min.

In other words, if you only bump thread_pool_min, you automatically
bump thread_pool_reserve.

In my previous suggestion my mighty arithmetic powers had failed me.
5% of 2000 is obviously 100, so a thread_pool_reserve of 500 was no
longer in the same ballpark.

> On the primary one you can see decreasing the client.req in varnishstat two seconds after restarting hitch with H/2 enabled. It jumps from 100req/s to 1700req/s from one second to the next.

Like I said, until that deadlock is fixed:

    That would postpone the deadlock to higher concurrent traffic.

Tweaking the worker pools won't fix the problem, and in that regard h2
traffic is even more peaky (per user) than h1 because browsers will
typically ask resources immediately (where h1 TCP pooling would
prevent too much concurrency) so seeing such peaks is not really

Thanks for sharing your experience nevertheless :)


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