DOC: config: provide some configuration hints for "http-reuse"
This adds some configuration hints regarding various workloads that do
not manage to achieve high reuse rates due to too low a global maxconn
or thread groups.
This fixes github issue #1472.
(cherry picked from commit 44fce8bd73cc743afc7e7f3f70a5a177a9557e62)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
(cherry picked from commit e3bafd59809a6647c5e2d8950ab0ca50b2dd5d12)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
(cherry picked from commit 200559b929da4643866a39397b4a985af5466300)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
diff --git a/doc/configuration.txt b/doc/configuration.txt
index fa246ff..45b2e66 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -7547,7 +7547,26 @@
because almost no new connection will be established while idle connections
remain available. This is particularly true with the "always" strategy.
- See also : "option http-keep-alive", "server maxconn"
+ The rules to decide to keep an idle connection opened or to close it after
+ processing are also governed by the "tune.pool-low-fd-ratio" (default: 20%)
+ and "tune.pool-high-fd-ratio" (default: 25%). These correspond to the
+ percentage of total file descriptors spent in idle connections above which
+ haproxy will respectively refrain from keeping a connection opened after a
+ response, and actively kill idle connections. Some setups using a very high
+ ratio of idle connections, either because of too low a global "maxconn", or
+ due to a lot of HTTP/2 or HTTP/3 traffic on the frontend (few connections)
+ but HTTP/1 connections on the backend, may observe a lower reuse rate because
+ too few connections are kept open. It may be desirable in this case to adjust
+ such thresholds or simply to increase the global "maxconn" value.
+
+ Similarly, when thread groups are explicitly enabled, it is important to
+ understand that idle connections are only usable between threads from a same
+ group. As such it may happen that unfair load between groups leads to more
+ idle connections being needed, causing a lower reuse rate. The same solution
+ may then be applied (increase global "maxconn" or increase pool ratios).
+
+ See also : "option http-keep-alive", "server maxconn", "thread-groups",
+ "tune.pool-high-fd-ratio", "tune.pool-low-fd-ratio"
http-send-name-header [<header>]