Incremental eviction processing (#7653)

Rather than blindly evicting until maxmemory limit is achieved, this
update adds a time limit to eviction.  While over the maxmemory limit,
eviction will process before each command AND as a timeProc when no
commands are running.

This will reduce the latency impact on many cases, especially pathological
cases like massive used memory increase during dict rehashing.

There is a risk that some other edge cases (like massive pipelined use
of MGET) could cause Redis memory usage to keep growing despite the
eviction attempts, so a new maxmemory-eviction-tenacity config is
introduced to let users mitigate that.

1 files changed, 8 insertions, 0 deletions

diff --git a/redis.conf b/redis.conf
index 51f71484c..424dfa09a 100644
--- a/redis.conf
+++ b/redis.conf
@@ -912,6 +912,14 @@ acllog-max-len 128
 #
 # maxmemory-samples 5
 
+# Eviction processing is designed to function well with the default setting.
+# If there is an unusually large amount of write traffic, this value may need to
+# be increased.  Decreasing this value may reduce latency at the risk of 
+# eviction processing effectiveness
+#   0 = minimum latency, 10 = default, 100 = process without regard to latency
+#
+# maxmemory-eviction-tenacity 10
+
 # Starting from Redis 5, by default a replica will ignore its maxmemory setting
 # (unless it is promoted to master after a failover or manually). It means
 # that the eviction of keys will be just handled by the master, sending the