Compressed dictionaries inside of LowCardinality. WIP#80356
Open
Krytog wants to merge 61 commits intoClickHouse:masterfrom
Open
Compressed dictionaries inside of LowCardinality. WIP#80356Krytog wants to merge 61 commits intoClickHouse:masterfrom
Krytog wants to merge 61 commits intoClickHouse:masterfrom
Conversation
|
|
nikitamikhaylov
added
the
can be tested
Contributor
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
3 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Changelog category (leave one):
Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):
Add in-memory compressed dictionary for LowCardinality to reduce memory consumption and enhance throughput
Documentation entry for user-facing changes
Adds session settings
low_cardinality_experimental_compressionandlow_cardinality_compression_fc_block_parameter. These settings are used to enable in-memory front coding compression of dictionaries inside ofLowCardinality(String). It greatly reduces memory consumption at the cost of some execution speed. Overall throughput is enhanced. Especially useful when there are high numbers of unique elements in a column.Technical details: compression is implemented via a
ColumnUniqueCompressedcolumn that contains compressed data and can be used inside of LowCardinality. A lot of changes are made to enable all the systems to work with LowCardinality columns with compressed dictionaries inside.Some additional optimizations are in development.