User-defined switch point between sparse-dense HLL encodings.

1 files changed, 14 insertions, 0 deletions

diff --git a/redis.conf b/redis.conf
index 1e53917b6..ee3a3a3ce 100644
--- a/redis.conf
+++ b/redis.conf
@@ -682,6 +682,20 @@ set-max-intset-entries 512
 zset-max-ziplist-entries 128
 zset-max-ziplist-value 64
 
+# HyperLogLog sparse representation bytes limit. The limit includes the
+# 16 bytes header. When an HyperLogLog using the sparse representation crosses
+# this limit, it is convereted into the dense representation.
+#
+# A value greater than 16000 is totally useless, since at that point the
+# dense representation is more memory efficient.
+# 
+# The suggested value is ~ 3000 in order to have the benefits of
+# the space efficient encoding without slowing down too much PFADD,
+# which is O(N) with the sparse encoding. Thev value can be raised to
+# ~ 10000 when CPU is not a concern, but space is, and the data set is
+# composed of many HyperLogLogs with cardinality in the 0 - 15000 range.
+hll-sparse-max-bytes 3000
+
 # Active rehashing uses 1 millisecond every 100 milliseconds of CPU time in
 # order to help rehashing the main Redis hash table (the one mapping top-level
 # keys to values). The hash table implementation Redis uses (see dict.c)