Redis HyperLogLog: PFMERGE

Redis PFMERGE Command

Redis PFMERGE command is used to merge multiple HyperLogLog values into a unique value that will approximate the cardinality of the union of the observed Sets of the source HyperLogLog structures.

Here are some common uses and scenarios for the "PFMERGE" command:

• Combining Estimates: Merges multiple HyperLogLog structures into a single HyperLogLog, combining their unique element estimates.
• Aggregated Cardinality: Provides an approximate count of unique elements from multiple data sources or datasets.
• Distributed Counting: Useful for distributed systems where unique element counts from different nodes need to be aggregated.
• Data Analysis: Facilitates data analysis by merging HyperLogLogs representing different time periods or categories to get a combined unique count.

Syntax:

PFMERGE KEY1 KEY@... KEYN

Available since

2.8.9.

Return Value

Simple string reply OK

Return Value Type

String

Example: Redis PFMERGE

redis 127.0.0.1:6379> PFADD hll1 foo bar zap a
(integer) 1
redis 127.0.0.1:6379> PFADD hll2 a b c foo
(integer) 1
redis 127.0.0.1:6379> PFMERGE hll3 hll1 hll2
OK
redis 127.0.0.1:6379> PFCOUNT hll3
(integer) 6

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