Redis HyperLogLog: PFCOUNT

Redis PFCOUNT Command

Redis PFCOUNT command is used to get the approximated cardinality computed by the HyperLogLog data structure stored in the specified variable. If the key does not exist, then it returns 0.

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

• Approximate Cardinality Estimation: Returns the approximate number of unique elements added to the specified HyperLogLog data structure.
• Efficient Counting: Provides a memory-efficient method to count unique elements in large datasets without storing all elements.
• Monitoring and Analytics: Useful for monitoring and analytics tasks, such as tracking unique visitors to a website or unique events in a log.
• Big Data Applications: Ideal for big data applications where precise counts are not necessary, but approximate counts are sufficient.

Syntax:

PFCOUNT KEY1 KEY@... KEYN

Available since

2.8.9.

Return Value

Integer reply approximated a number of unique elements.

When PFCOUNT command is used with multiple keys, then it returns approximated cardinality of the union of the HyperLogLogs.

Return Value Type

Integer

Example: Redis PFCOUNT

redis 127.0.0.1:6379> PFADD mykey a b c d e f g h i j
(integer) 1
redis 127.0.0.1:6379> PFCOUNT mykey
(integer) 10
redis 127.0.0.1:6379> PFCOUNT mykey
(integer) 10
redis 127.0.0.1:6379> PFCOUNT mykey mynewkey
(integer) 10

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