> For the complete documentation index, see [llms.txt](https://rc.sunbird.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://rc.sunbird.org/use/developer-guide/backup-and-restore/cassandra.md).

# Cassandra

SSTables live under the keyspace directory (default `/var/lib/cassandra/data/`), per the path in `cassandra.yaml`.

## Backup

{% tabs %}
{% tab title="Snapshot-based" %}
Via `nodetool snapshot`, which flushes memtables and hard-links SSTables.

```bash
nodetool snapshot                                  # all keyspaces
nodetool snapshot -t 2023.06.27 organization       # one keyspace, named
nodetool snapshot --table employee organization    # one table
```

Transfer snapshots off-box (S3, GCS, Azure) afterward. `nodetool clearsnapshot` removes them locally.

{% hint style="warning" %}
Snapshots don't back up the schema — do that separately.
{% endhint %}

* *Advantages*: simple, easy to manage.
* *Disadvantages*: daily full-keyspace snapshots don't scale well for large datasets; transfer to cold storage can get expensive.
  {% endtab %}

{% tab title="Incremental" %}
Set `incremental_backups: true` in `cassandra.yaml`. Cassandra then hard-links newly-flushed SSTables into a backup directory as they're written, on top of the last full snapshot.

* *Advantages*: lower disk usage, lower transfer cost.
* *Disadvantages*: Cassandra doesn't clean these up automatically (you need your own pruning script); produces many small files; can't selectively back up individual column families.
  {% endtab %}
  {% endtabs %}

## Data Restore

{% tabs %}
{% tab title="nodetool refresh" %}
Loads newly-placed SSTables without a restart.

1. Create the schema if missing
2. Truncate the table if needed
3. Copy the snapshot's SSTable directory into place
4. Run `nodetool refresh`
   {% endtab %}

{% tab title="sstableloader" %}
Loads a set of SSTables into a running cluster — works for external data, existing SSTables, or snapshot restores:

```bash
sstableloader -d <ip> /home/data
```

Create the schema and truncate the table first if needed.
{% endtab %}
{% endtabs %}


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