# Sketch Functions

Pinot supports several sketch-based algorithms for approximate distinct counting and summarization. These functions trade a small amount of accuracy for significant memory and performance savings at scale.

For exact distinct counting, see [DISTINCTCOUNT](/functions/aggregation/distinctcount.md).

## CPC Sketch

The [Compressed Probability Counting (CPC) Sketch](https://datasketches.apache.org/docs/CPC/CPC.html) enables extremely space-efficient cardinality estimation — about 40% less space than an HLL sketch of comparable accuracy.

| Function                                                                    | Description                                         |
| --------------------------------------------------------------------------- | --------------------------------------------------- |
| [DISTINCTCOUNTCPCSKETCH](/functions/sketch/distinctcountcpcsketch.md)       | Returns approximate distinct count using CPC sketch |
| [DISTINCTCOUNTRAWCPCSKETCH](/functions/sketch/distinctcountrawcpcsketch.md) | Returns raw CPC sketch as hex string                |

## HyperLogLog Plus

HyperLogLogPlus (HLL++) provides approximate distinct counts with configurable precision (`p`, `sp` parameters).

| Function                                                                                         | Description                                          |
| ------------------------------------------------------------------------------------------------ | ---------------------------------------------------- |
| [DISTINCTCOUNTHLLPLUS](/functions/sketch/distinctcounthllplus.md)                                | Approximate distinct count using HLL++               |
| [DISTINCTCOUNTSMARTHLLPLUS](/functions/sketch/distinctcounthllplus.md#distinctcountsmarthllplus) | Starts exact and converts to HLL++ after a threshold |
| [DISTINCTCOUNTHLLPLUSMV](/functions/sketch/distinctcounthllplusmv.md)                            | HLL++ for multi-value columns                        |
| [DISTINCTCOUNTRAWHLLPLUS](/functions/sketch/distinctcountrawhllplus.md)                          | Returns serialized HLL++ sketch                      |
| [DISTINCTCOUNTRAWHLLPLUSMV](/functions/sketch/distinctcountrawhllplusmv.md)                      | Serialized HLL++ sketch for multi-value columns      |

## UltraLogLog

The [UltraLogLog Sketch](https://arxiv.org/abs/2308.16862) from Dynatrace requires less space than HyperLogLog and provides a simpler, faster estimator. Implemented via [Hash4j](https://github.com/dynatrace-oss/hash4j/tree/main).

| Function                                                        | Description                                         |
| --------------------------------------------------------------- | --------------------------------------------------- |
| [DISTINCTCOUNTULL](/functions/sketch/distinctcountull.md)       | Approximate distinct count using ULL (default p=12) |
| [DISTINCTCOUNTRAWULL](/functions/sketch/distinctcountrawull.md) | Returns serialized ULL sketch                       |

## Tuple Sketch

The [Tuple Sketch](https://datasketches.apache.org/docs/Tuple/TupleOverview.html) extends the Theta Sketch with additional summary values per entry, ideal for summarizing attributes like impressions or clicks.

| Function                                                                                            | Description                      |
| --------------------------------------------------------------------------------------------------- | -------------------------------- |
| [DISTINCTCOUNTTUPLESKETCH](/functions/sketch/distinctcounttuplesketch.md)                           | Distinct count from tuple sketch |
| [DISTINCTCOUNTRAWINTEGERSUMTUPLESKETCH](/functions/sketch/distinctcountrawintegersumtuplesketch.md) | Raw tuple sketch as hex          |
| [AVGVALUEINTEGERSUMTUPLESKETCH](/functions/sketch/avgvalueintegersumtuplesketch.md)                 | Average of summary values        |
| [SUMVALUESINTEGERSUMTUPLESKETCH](/functions/sketch/sumvaluesintegersumtuplesketch.md)               | Sum of summary values            |

## Frequency Sketches

| Function                                                            | Description                             |
| ------------------------------------------------------------------- | --------------------------------------- |
| [FREQUENTLONGSSKETCH](/functions/sketch/frequentlongssketch.md)     | Frequent items sketch for long values   |
| [FREQUENTSTRINGSSKETCH](/functions/sketch/frequentstringssketch.md) | Frequent items sketch for string values |


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