Expire cycle: document expire effort in redis.conf.

1 files changed, 20 insertions, 3 deletions

diff --git a/redis.conf b/redis.conf
index 0ec3321a5..39e21b5e7 100644
--- a/redis.conf
+++ b/redis.conf
@@ -813,11 +813,11 @@ replica-priority 100
 # MAXMEMORY POLICY: how Redis will select what to remove when maxmemory
 # is reached. You can select among five behaviors:
 #
-# volatile-lru -> Evict using approximated LRU among the keys with an expire set.
+# volatile-lru -> Evict using approximated LRU, only keys with an expire set.
 # allkeys-lru -> Evict any key using approximated LRU.
-# volatile-lfu -> Evict using approximated LFU among the keys with an expire set.
+# volatile-lfu -> Evict using approximated LFU, only keys with an expire set.
 # allkeys-lfu -> Evict any key using approximated LFU.
-# volatile-random -> Remove a random key among the ones with an expire set.
+# volatile-random -> Remove a random key having an expire set.
 # allkeys-random -> Remove a random key, any key.
 # volatile-ttl -> Remove the key with the nearest expire time (minor TTL)
 # noeviction -> Don't evict anything, just return an error on write operations.
@@ -872,6 +872,23 @@ replica-priority 100
 #
 # replica-ignore-maxmemory yes
 
+# Redis reclaims expired keys in two ways: upon access when those keys are
+# found to be expired, and also in background, in what is called the
+# "active expire key". The key space is slowly and interactively scanned
+# looking for expired keys to reclaim, so that it is possible to free memory
+# of keys that are expired and will never be accessed again in a short time.
+#
+# The default effort of the expire cycle will try to avoid having more than
+# ten percent of expired keys still in memory, and will try to avoid consuming
+# more than 25% of total memory and to add latency to the system. However
+# it is possible to increase the expire "effort" that is normally set to
+# "1", to a greater value, up to the value "10". At its maximum value the
+# system will use more CPU, longer cycles (and technically may introduce
+# more latency), and will tollerate less already expired keys still present
+# in the system. It's a tradeoff betweeen memory, CPU and latecy.
+#
+# active-expire-effort 1
+
 ############################# LAZY FREEING ####################################
 
 # Redis has two primitives to delete keys. One is called DEL and is a blocking