ScyllaDB University LIVE, FREE Virtual Training Event | March 21
Register for Free
ScyllaDB Documentation Logo Documentation
  • Server
  • Cloud
  • Tools
    • ScyllaDB Manager
    • ScyllaDB Monitoring Stack
    • ScyllaDB Operator
  • Drivers
    • CQL Drivers
    • DynamoDB Drivers
  • Resources
    • ScyllaDB University
    • Community Forum
    • Tutorials
Download
ScyllaDB Docs ScyllaDB Open Source Scylla Architecture Scylla SSTable Format Scylla SSTable - 2.x SSTable Compression

Caution

You're viewing documentation for a previous version. Switch to the latest stable version.

SSTable Compression¶

Chunked Compression of Data File¶

SSTables compression allows to optionally compress the SSTables Data File, which is the biggest part of the SSTable (the other parts, like the index, cannot be compressed).

Because random-access read from the data file is important, Apache Cassandra implements chunked compression: The uncompressed file is divided into chunks of a configurable fixed size (usually 64 KB), and each of these chunks is compressed separately and written to the compressed data file, followed by a 4-byte checksum of the compressed chunk. The compressed chunks have different lengths, so we need to remember their offsets so we can seek to an arbitrary chunk containing our desired uncompressed data. This list of offsets is stored in a separate Compression Info File, described below.

The Compression Info File¶

References: CompressedRandomAccessReader.java, CompressionMetadata.java, CompressionParameters.java.

The Compression Info File only exists if the data file is compressed. The Compression Info File specifies the compression parameters that the decompressor needs to know (such as the compression algorithm and chunk size), and the list of offsets of the compressed chunks in the compressed file:

struct short_string {
    be16 length;
    char value[length];
};
struct option {
    short_string key;
    short_string value;
};
struct compression_info {
    short_string compressor_name;
    be32 options_count;
    option options[options_count];
    be32 chunk_length;
    be64 data_length;
    be32 chunk_count;
    be64 chunk_offsets[chunk_count];
};

The compressor_name can be one of three strings supported by Apache Cassandra: “LZ4Compressor”, “SnappyCompressor” or “DeflateCompressor”. Cassandra defaults to LZ4Compressor, but a user could choose any one of the three.

The options may contain additional options for the decompressor, But usually no options are listed, and only one option exists: “crc_check_chance”, whose value is a floating-point string which defaults (if the option doesn’t appear) to “1.0”, and determines the probability that we verify the checksum of a compressed chunk we read.

chunk_length is the length of the chunks into which the original uncompressed data is divided before compression. The decompressor needs to know this chunk size as well, so when given a desired byte offset in the original uncompressed file, it can determine which chunk it needs to uncompress. The chunk length defaults to 65536 bytes, but can be any power of two.

data_length is the total length of the uncompressed data.

chunks_offsets is the list of offsets of the compressed chunks inside the compressed file. To read data in position p in the uncompressed file, we calculates p / chunk_length is the uncompressed chunk number. The compressed version of this check is now begins in chunk_offsets[p / chunk_length]. The compressed chunk ends 4 bytes before the beginning of the next chunk (because, as explained above, every compressed chunk is followed by a 4-byte checksum).

The Compressed Data File¶

As explained above, the compressed data file is a sequence of compressed chunked, each a compressed version of a fixed-sized (chunk_length from the Compression Info File) uncompressed chunk. Each compressed chunk is followed by a be32 (big-endian 4-byte integer) Adler32 checksum of the compressed data, which can be used to verify the data hasn’t been corrupted

Scylla Architecture

Copyright

© 2016, The Apache Software Foundation.

Apache®, Apache Cassandra®, Cassandra®, the Apache feather logo and the Apache Cassandra® Eye logo are either registered trademarks or trademarks of the Apache Software Foundation in the United States and/or other countries. No endorsement by The Apache Software Foundation is implied by the use of these marks.

Was this page helpful?

PREVIOUS
Scylla SSTable - 2.x
NEXT
SSTable Data File
  • Create an issue
  • Edit this page

On this page

  • SSTable Compression
    • Chunked Compression of Data File
    • The Compression Info File
    • The Compressed Data File
ScyllaDB Open Source
  • 5.1
    • master
    • 6.2
    • 6.1
    • 6.0
    • 5.4
    • 5.2
    • 5.1
  • Getting Started
    • Install Scylla
      • ScyllaDB Web Installer for Linux
      • Scylla Unified Installer (relocatable executable)
      • Air-gapped Server Installation
      • What is in each RPM
      • Scylla Housekeeping and how to disable it
      • Scylla Developer Mode
      • Scylla Configuration Reference
    • Configure Scylla
    • ScyllaDB Requirements
      • System Requirements
      • OS Support by Platform and Version
      • Scylla in a Shared Environment
    • Migrate to ScyllaDB
      • Migration Process from Cassandra to Scylla
      • Scylla and Apache Cassandra Compatibility
      • Migration Tools Overview
    • Integration Solutions
      • Integrate Scylla with Spark
      • Integrate Scylla with KairosDB
      • Integrate Scylla with Presto
      • Integrate Scylla with Elasticsearch
      • Integrate Scylla with Kubernetes
      • Integrate Scylla with the JanusGraph Graph Data System
      • Integrate Scylla with DataDog
      • Integrate Scylla with Kafka
      • Integrate Scylla with IOTA Chronicle
      • Integrate Scylla with Spring
      • Shard-Aware Kafka Connector for Scylla
      • Install Scylla with Ansible
      • Integrate Scylla with Databricks
    • Tutorials
  • Scylla for Administrators
    • Administration Guide
    • Procedures
      • Cluster Management
      • Backup & Restore
      • Change Configuration
      • Maintenance
      • Best Practices
      • Benchmarking Scylla
      • Migrate from Cassandra to Scylla
      • Disable Housekeeping
    • Security
      • Scylla Security Checklist
      • Enable Authentication
      • Enable and Disable Authentication Without Downtime
      • Generate a cqlshrc File
      • Reset Authenticator Password
      • Enable Authorization
      • Grant Authorization CQL Reference
      • Role Based Access Control (RBAC)
      • Scylla Auditing Guide
      • Encryption: Data in Transit Client to Node
      • Encryption: Data in Transit Node to Node
      • Generating a self-signed Certificate Chain Using openssl
      • Encryption at Rest
      • LDAP Authentication
      • LDAP Authorization (Role Management)
    • Admin Tools
      • Nodetool Reference
      • CQLSh
      • REST
      • Tracing
      • Scylla SStable
      • Scylla Types
      • SSTableLoader
      • cassandra-stress
      • SSTabledump
      • SSTable2json
      • SSTable Index
      • Scylla Logs
      • Seastar Perftune
      • Virtual Tables
    • ScyllaDB Monitoring Stack
    • ScyllaDB Operator
    • ScyllaDB Manager
    • Upgrade Procedures
      • Scylla Enterprise
      • Scylla Open Source
      • Scylla Open Source to Scylla Enterprise
      • Scylla AMI
    • System Configuration
      • System Configuration Guide
      • scylla.yaml
      • Scylla Snitches
    • Benchmarking Scylla
  • Scylla for Developers
    • Learn To Use Scylla
      • Scylla University
      • Course catalog
      • Scylla Essentials
      • Basic Data Modeling
      • Advanced Data Modeling
      • MMS - Learn by Example
      • Care-Pet an IoT Use Case and Example
    • Scylla Alternator
    • Scylla Features
      • Scylla Open Source Features
      • Scylla Enterprise Features
    • Scylla Drivers
      • Scylla CQL Drivers
      • Scylla DynamoDB Drivers
  • CQL Reference
    • CQLSh: the CQL shell
    • Appendices
    • Compaction
    • Consistency Levels
    • Consistency Level Calculator
    • Data Definition
    • Data Manipulation
    • Data Types
    • Definitions
    • Global Secondary Indexes
    • Additional Information
    • Expiring Data with Time to Live (TTL)
    • Additional Information
    • Functions
    • JSON Support
    • Materialized Views
    • Non-Reserved CQL Keywords
    • Reserved CQL Keywords
    • ScyllaDB CQL Extensions
  • Scylla Architecture
    • Scylla Ring Architecture
    • Scylla Fault Tolerance
    • Consistency Level Console Demo
    • Scylla Anti-Entropy
      • Scylla Hinted Handoff
      • Scylla Read Repair
      • Scylla Repair
    • SSTable
      • Scylla SSTable - 2.x
      • ScyllaDB SSTable - 3.x
    • Compaction Strategies
    • Raft Consensus Algorithm in ScyllaDB
  • Troubleshooting Scylla
    • Errors and Support
      • Report a Scylla problem
      • Error Messages
      • Change Log Level
    • Scylla Startup
      • Ownership Problems
      • Scylla will not Start
      • Scylla Python Script broken
    • Cluster and Node
      • Failed Decommission Problem
      • Cluster Timeouts
      • Node Joined With No Data
      • SocketTimeoutException
      • NullPointerException
    • Data Modeling
      • Scylla Large Partitions Table
      • Scylla Large Rows and Cells Table
      • Large Partitions Hunting
    • Data Storage and SSTables
      • Space Utilization Increasing
      • Disk Space is not Reclaimed
      • SSTable Corruption Problem
      • Pointless Compactions
      • Limiting Compaction
    • CQL
      • Time Range Query Fails
      • COPY FROM Fails
      • CQL Connection Table
      • Reverse queries fail
    • Scylla Monitor and Manager
      • Manager and Monitoring integration
      • Manager lists healthy nodes as down
  • Knowledge Base
    • Upgrading from experimental CDC
    • Compaction
    • Counting all rows in a table is slow
    • CQL Query Does Not Display Entire Result Set
    • When CQLSh query returns partial results with followed by “More”
    • Run Scylla and supporting services as a custom user:group
    • Decoding Stack Traces
    • Snapshots and Disk Utilization
    • DPDK mode
    • Debug your database with Flame Graphs
    • How to Change gc_grace_seconds for a Table
    • Gossip in Scylla
    • Increase Permission Cache to Avoid Non-paged Queries
    • How does Scylla LWT Differ from Apache Cassandra ?
    • Map CPUs to Scylla Shards
    • Scylla Memory Usage
    • NTP Configuration for Scylla
    • Updating the Mode in perftune.yaml After a ScyllaDB Upgrade
    • POSIX networking for Scylla
    • Scylla consistency quiz for administrators
    • Recreate RAID devices
    • How to Safely Increase the Replication Factor
    • Scylla and Spark integration
    • Increase Scylla resource limits over systemd
    • Scylla Seed Nodes
    • How to Set up a Swap Space
    • Scylla Snapshots
    • Scylla payload sent duplicated static columns
    • Stopping a local repair
    • System Limits
    • How to flush old tombstones from a table
    • Time to Live (TTL) and Compaction
    • Scylla Nodes are Unresponsive
    • Update a Primary Key
    • Using the perf utility with Scylla
    • Configure Scylla Networking with Multiple NIC/IP Combinations
  • ScyllaDB University
  • Scylla FAQ
  • Contribute to ScyllaDB
  • Glossary
  • Alternator: DynamoDB API in Scylla
    • Getting Started With ScyllaDB Alternator
    • Scylla Alternator for DynamoDB users
Docs Tutorials University Contact Us About Us
© 2025, ScyllaDB. All rights reserved. | Terms of Service | Privacy Policy | ScyllaDB, and ScyllaDB Cloud, are registered trademarks of ScyllaDB, Inc.
Last updated on 13 May 2025.
Powered by Sphinx 7.4.7 & ScyllaDB Theme 1.8.6