The document discusses the SSTables 3.0 file format, an upgrade from older formats used in Cassandra for data storage, emphasizing improvements in data representation, reduced duplication, and increased processing efficiency. Key benefits include significant disk space savings, faster row processing, and compatibility with both old and new SSTables. Users can natively import Cassandra 3.x files to Scylla, enjoy better performance, and can upgrade old SSTables through compaction.

1. SSTables 3.0 File Format
Vladimir Krivopalov
Software Developer at ScyllaDB

2. About me
A software developer with over 10 years of experience
currently working on ScyllaDB.
Areas of expertise include server-side networking services,
secure gateway for remote desktop access, reverse proxy for
web and many others. Hold an MS degree in applied
mathematics from the Tomsk State University, and enjoy
modern C++, high performance, open source and cutting-edge
technologies.

3. Introduction

4. Introduction
SSTables is a Cassandra format for storing data on disk.
▪ ka (since Cassandra 2.1)
▪ la/lb (since Cassandra 2.2)
▪ ma/mb/mc (since Cassandra 3.0)
Supported today (ka/la)
Coming in Scylla 3.0 (mc)

5. Old SSTables Format

6. Old SSTables Format
Old formats, ‘kX’ and ‘lX’, are identical in how they store data:
Partition
Cell Cell Cell

7. Old SSTables Format
Cell
<clustering key value>:<column name>
<column value>

8. Old SSTables Format
What are the problems with this format?
▪ Not aligned with CQL, same-row cells not grouped
▪ Lots of data duplication - repetitive clustering keys and column
names across cells, timestamps, TTLs, etc
▪ Ad-hoc solutions that look like hacks (e.g., row markers)
▪ Linear search through promoted index for wide partitions

9. New SSTables Format

10. New SSTables Format
Partition
Row
Cell Cell Cell
Row
Cell Cell Cell

11. New SSTables Format
▪ Internal representation aligned with CQL model
▪ Variable-length integers and delta-based encoding
▪ Information about columns is stored in Statistics.db
▪ Inherent row attributes (row marker -> liveness info)

12. New SSTables Format
✓ Noticeable disk space savings (10-80% smaller data files)
✓ Easier (means faster) processing of rows
✓ Files don’t depend on schema
✓ Binary search through index: O(log n) instead of O(n)
• Is not supported in Scylla 3.0 - work in progress

13. What Does It Mean For Users

14. What Does It Mean For Users
▪ Files from Cassandra 3.x can be imported natively to Scylla
▪ Consider disabling compression for lower latency
▪ No reason to use compact tables any longer
▪ Better performance and disk space savings!

15. What Does It Mean For Users
In 3.0:
▪ Writing and reading SSTables 3.0. Old formats supported too.
▪ Upgrade of old SSTables to new format through compaction.
In 3.x (future releases):
▪ Binary search through promoted index on sliced reads.
▪ Caching of promoted index blocks.
▪ Write in new format only (reading old formats still supported).

16. Thank You
Any Questions ?
Please stay in touch
vladimir@scylladb.com
@argenetix