# SSTable ms Index: Trie-Based Format The `ms` format introduces a trie-based partition index, replacing the previous Cassandra 3.0 index format used by `me` and `md`. ## Benefits Compared to the previous format, the trie-based index provides: * **Reduced memory footprint** - less in-memory index data per SSTable. * **Faster partition lookups** - more efficient index traversal. * **Smaller on-disk index files** - shared key prefixes reduce redundant storage. ## Configuring ms Format ### New Clusters (2026.2 and Later) Starting with ScyllaDB 2026.2, `ms` is the default value for `sstable_format` in the default `scylla.yaml`. Clusters created with ScyllaDB 2026.2 use the `ms` format unless the configuration is changed. ### Upgraded Clusters Clusters upgraded from an earlier version continue to use the format specified in their `scylla.yaml`. To switch to the `ms` format, add the following to `scylla.yaml`: ```yaml sstable_format: ms ``` After the node configuration is updated, newly created SSTables will use the `ms` format. Existing SSTables are not automatically converted. They will be rewritten in `ms` format during the next compaction. Conversion can be triggered using `nodetool upgradesstables -a` after updating the node configuration. ## Related Topics * [SSTable 3.0 Format in ScyllaDB](https://docs.scylladb.com/manual/master/architecture/sstable/sstable3/sstable-format.md) - overview of 3.x format variants