Data Pruning

Algorithms/Data Structures
Updated on:
April 16, 2024

What is data pruning?

Data pruning is the process of excluding irrelevant data when processing database queries in order to minimize the amount of data read, processed, and transferred. Databases employ techniques to analyze queries and safely eliminate portions of datasets, partitions, indexes, and rows that cannot influence the query result.

This reduces disk I/O, memory, CPU costs and network traffic - enabling faster processing for complex analytical queries over large datasets. Advanced cost-based optimizers automatically determine what data can be pruned.

Some pruning techniques include partition elimination, row-level security filtering, and using collision-resistant hash functions for efficient filtering with Count-Min Sketches. Intelligent data pruning is key for performant analytics.

How does data pruning work?

Common data pruning techniques include:

  • Partition pruning - Eliminate partitions not applicable based on query criteria.
  • Index pruning - Scan only useful index ranges, skip irrelevant entries.
  • Row pruning - Filter out rows that don't satisfy query conditions.
  • Column pruning - Read only columns required for the query.

Database statistics about data distribution, indexes, and constraints enable identifying pruning opportunities during query optimization.

Why is data pruning important?

Data pruning provides major performance gains for analytical workloads, especially in massively parallel processing systems. Eliminating irrelevant data portions directly reduces IO, memory, CPU costs - letting queries run faster.

Pruning enables scaling to larger data volumes by minimizing what data is processed. In fasting growing datasets, pruning often makes the difference between feasible and infeasible queries.

FAQ

When does data pruning provide the biggest gains?

Data pruning provides the largest gains for:

  • Analytics running complex queries over huge datasets.
  • Massively parallel systems where pruning entire partitions or nodes is impactful.
  • Situations where query selectivity is low, eliminating larger portions.

What are some limitations of data pruning?

Some challenges around extensive pruning:

  • Over-pruning can cause incorrect results if statistics are stale.
  • Estimation errors can lead to non-optimal pruning.
  • Hard to prune unstructured data lacking metadata like indexes.
  • Careful tuning needed to balance pruning vs overhead.

What are some advanced data pruning techniques?

Some advanced techniques include:

  • Columnar compression schemes that cluster data.
  • Zone maps recording min/max values for blocks.
  • Machine learning to estimate query effectiveness of pruning.
  • Multi-column statistics and correlation tracking.
  • Spatial pruning for geographic queries.

References:

Related Entries

Count Min Sketch

A Count Min Sketch is a probabilistic data structure used to estimate item frequencies and counts in data streams.

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Collision Resistance

Collision resistance is the property of cryptographic hash functions to minimize chances of different inputs mapping to the same output hash, making it difficult to intentionally cause collisions.

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Hash Functions

Hash functions are algorithms that map data of arbitrary size to fixed-size values called hashes in a deterministic, one-way manner for purposes like data integrity and database lookup.

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