[master] 5d713b2 improve ban_cutoff documentation based on a question on -misc

Nils Goroll nils.goroll at uplex.de
Wed Aug 30 15:19:06 CEST 2017


commit 5d713b2d8a796c6d21c2066d8ef1e0beab690dd4
Author: Nils Goroll <nils.goroll at uplex.de>
Date:   Wed Aug 30 15:18:13 2017 +0200

    improve ban_cutoff documentation based on a question on -misc

diff --git a/include/tbl/params.h b/include/tbl/params.h
index fc25054..91cfd66 100644
--- a/include/tbl/params.h
+++ b/include/tbl/params.h
@@ -146,10 +146,18 @@ PARAM(
 	/* flags */	EXPERIMENTAL,
 	/* s-text */
 	"Expurge long tail content from the cache to keep the number of bans "
-	"below this value. 0 disables.\n"
-	"This is a safety net to avoid bad response times due to bans being "
-	"tested at lookup time. Setting a cutoff trades response time for "
-	"cache efficiency. The recommended value is proportional to "
+	"below this value. 0 disables.\n\n"
+	"When this parameter is set to a non-zero value, the ban lurker "
+	"continues to work the ban list as usual top to bottom, but when it "
+	"reaches the ban_cutoff-th ban, it treats all objects as if they "
+	"matched a ban and expurges them from cache. As actively used objects "
+	"get tested against the ban list at request time and thus are likely "
+	"to be associated with bans near the top of the ban list, with "
+	"ban_cutoff, least recently accessed objects (the \"long tail\") are "
+	"removed.\n\n"
+	"This parameter is a safety net to avoid bad response times due to "
+	"bans being tested at lookup time. Setting a cutoff trades response "
+	"time for cache efficiency. The recommended value is proportional to "
 	"rate(bans_lurker_tests_tested) / n_objects while the ban lurker is "
 	"working, which is the number of bans the system can sustain. The "
 	"additional latency due to request ban testing is in the order of "



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