estimateCompressionRatio

Introduced in: v25.4.0

Estimates the compression ratio of a given column without compressing it.

Syntax

estimateCompressionRatio([codec, block_size_bytes])(column)

Parameters

codec — String containing a compression codec or multiple comma-separated codecs in a single string. String
block_size_bytes — Block size of compressed data. This is similar to setting both max_compress_block_size and min_compress_block_size. The default value is 1 MiB (1048576 bytes). Maximum allowed value is 256 MiB (268435456 bytes). UInt64

Arguments

column — Column of any type. Any

Returned value

Returns an estimate compression ratio for the given column. Float64

Examples

Basic usage with default codec

CREATE TABLE compression_estimate_example
(
    `number` UInt64
)
ENGINE = MergeTree()
ORDER BY number
SETTINGS min_bytes_for_wide_part = 0;

INSERT INTO compression_estimate_example
SELECT number FROM system.numbers LIMIT 100_000;

SELECT estimateCompressionRatio(number) AS estimate FROM compression_estimate_example

┌───────────estimate─┐
│ 1.9988506608699999 │
└────────────────────┘

Using a specific codec

SELECT estimateCompressionRatio('T64')(number) AS estimate FROM compression_estimate_example

┌──────────estimate─┐
│ 3.762758101688538 │
└───────────────────┘

Using multiple codecs

SELECT estimateCompressionRatio('T64, ZSTD')(number) AS estimate FROM compression_estimate_example

┌───────────estimate─┐
│ 143.60078980434392 │
└────────────────────┘