## How accurate is HyperLogLog?

The HyperLogLog algorithm is able to estimate cardinalities of > 109 with a typical accuracy (standard error) of 2%, using 1.5 kB of memory. HyperLogLog is an extension of the earlier LogLog algorithm, itself deriving from the 1984 Flajolet–Martin algorithm.

**When should I use HyperLogLog?**

One of the most important things to take away is that HyperLogLog is most effective when you are creating a structure for getting the answers to questions the business will need before you begin collecting the data.

**How accurate is HLL?**

As we discussed above, HLL is not 100% accurate. 99% of the time its margin of error is within 1%, with the remaining 1% of the time resulting in even larger margins of error. If the error does happen to be extremely large, it stands to reason that it would lead to extreme problems.

### What is Redis HyperLogLog?

Redis HyperLogLog is an algorithm that uses randomization in order to provide an approximation of the number of unique elements in a set using just a constant, and small amount of memory.

**What is FM algorithm in big data?**

Flajolet Martin Algorithm, also known as FM algorithm, is used to approximate the number of unique elements in a data stream or database in one pass. The highlight of this algorithm is that it uses less memory space while executing.

**What is cardinality algorithm?**

The cardinality of a finite set is the number of distinct elements in the set. For example, the cardinality of {5,3,12,1} is 4. Definition 2.3 (Multiset).

## What are HLL sketches?

HLL sketch is a construct that encapsulates the information about the distinct values in the data set. You can use HLL sketches to achieve significant performance benefits for queries that compute approximate cardinality over large data sets, with an average relative error between 0.01–0.6%.

**What is HyperLogLog ++ HLL and why is it used in Bigquery?**

HyperLogLog++ functions. The HyperLogLog++ algorithm (HLL++) estimates cardinality from sketches. If you do not want to work with sketches and do not need customized precision, consider using approximate aggregate functions with system-defined precision. HLL++ functions are approximate aggregate functions.

**Is Redis university free?**

Free online courses taught by Redis experts.

### What data types does Redis use to store a geospatial objects?

Redis lacks dedicated data types for geospatial objects. Instead, points are stored in sorted sets. The scores of the sets are used for encoding coordinate pairs.

**What clustering algorithms are good for big data?**

The 5 Clustering Algorithms Data Scientists Need to Know

- K-Means Clustering.
- Mean-Shift Clustering for a single sliding window.
- The entire process of Mean-Shift Clustering.
- DBSCAN Smiley Face Clustering.
- Two failure cases for K-Means.
- EM Clustering using GMMs.
- Agglomerative Hierarchical Clustering.

**Which algorithm we will implement to know how many distinct users?**