PFMERGE destkey sourcekey [sourcekey ...]
Available since: 2.8.9
Time complexity: O(N) to merge N HyperLogLogs, but with high constant times.
ACL categories:
@write
@hyperloglog
@slow
Merge multiple HyperLogLog values into an unique value that will approximate the cardinality of the union of the observed Sets of the source HyperLogLog structures.
The computed merged HyperLogLog is set to the destination variable, which is created if does not exist (defaulting to an empty HyperLogLog).
If the destination variable exists, it is treated as one of the source sets and its cardinality will be included in the cardinality of the computed HyperLogLog.
@return
@simple-string-reply: The command just returns OK.
@examples
redis> PFADD hll1 foo bar zap a
TBD
redis> PFADD hll2 a b c foo
TBD
redis> PFMERGE hll3 hll1 hll2
TBD
redis> PFCOUNT hll3