Distributed snapshots for YCQL

The most efficient way to back up the data stored in YugabyteDB is to create a distributed snapshot. A snapshot is a consistent cut of a data taken across all the nodes in the cluster.

When YugabyteDB creates a snapshot, it doesn't physically copy the data; instead, it creates hard links to all the relevant files. These links reside on the same storage volumes where the data itself is stored, which makes both backup and restore operations nearly instantaneous.

Note that even though there are no technical limitations on how many snapshots you can create, increasing the number of snapshots stored also increases the amount of space required for the database. The actual overhead depends on the workload, but you can estimate it by running tests based on your applications.

Create a snapshot

Using distributed snapshots allows you to back up a database and then restore it in case of a software or operational error, with minimal recovery time objectives (RTO) and overhead.

To back up a keyspace with all its tables and indexes, create a snapshot using the create_keyspace_snapshot command, as follows:

./bin/yb-admin -master_addresses <ip1:7100,ip2:7100,ip3:7100> create_keyspace_snapshot my_keyspace

To back up a single table with its indexes, use the create_snapshot command instead, as follows:

./bin/yb-admin -master_addresses <ip1:7100,ip2:7100,ip3:7100> create_snapshot my_keyspace my_table

When you execute either of the preceding commands, a unique ID for the snapshot is returned, as per the following output:

Started snapshot creation: a9442525-c7a2-42c8-8d2e-658060028f0e

You can then use this ID to check the status of the snapshot, delete it, or use it to restore the data.

Even though the create_keyspace_snapshot and create_snapshot commands exit immediately, the snapshot may take some time to complete. Before using the snapshot, verify its status with the list_snapshots command, as follows:

./bin/yb-admin -master_addresses <ip1:7100,ip2:7100,ip3:7100> list_snapshots

The preceding command lists the snapshots in the cluster, along with their states. You can find the ID of the new snapshot and make sure it has been completed, as shown in the following sample output:

Snapshot UUID                         State
a9442525-c7a2-42c8-8d2e-658060028f0e  COMPLETE

Delete a snapshot

Snapshots never expire and are retained as long as the cluster exists. If you no longer need a snapshot, you can delete it with the delete_snapshot command, as follows:

./bin/yb-admin -master_addresses <ip1:7100,ip2:7100,ip3:7100> delete_snapshot a9442525-c7a2-42c8-8d2e-658060028f0e

Restore a snapshot

To restore the data backed up in one of the previously created snapshots, run the restore_snapshot command, as follows:

./bin/yb-admin -master_addresses <ip1:7100,ip2:7100,ip3:7100> restore_snapshot a9442525-c7a2-42c8-8d2e-658060028f0e

This command rolls back the database to the state which it had when the snapshot was created. The restore happens in-place: it changes the state of the existing database within the same cluster.

Move a snapshot to external storage

Storing snapshots in-cluster is extremely efficient, but also comes with downsides. It can increase the cost of the cluster by inflating the space consumption on the storage volumes. Also, in-cluster snapshots don't protect you from a disaster scenario like filesystem corruption or a hardware failure.

To mitigate these issues, consider storing backups outside of the cluster, in cheaper storage that is also geographically separated from the cluster. This approach helps you to reduce the cost, and also to restore your databases into a different cluster, potentially in a different location.

To move a snapshot to external storage, gather all the relevant files from all the nodes, and copy them along with the additional metadata required for restores on a different cluster:

  1. Create an in-cluster snapshot.

  2. Create the snapshot metadata file by running the export_snapshot command and providing the ID of the snapshot:

    ./bin/yb-admin -master_addresses <ip1:7100,ip2:7100,ip3:7100> export_snapshot a9442525-c7a2-42c8-8d2e-658060028f0e my_keyspace.snapshot

  3. Copy the newly created snapshot metadata file (my_keyspace.snapshot) to the external storage.

  4. Copy the data files for all the tablets, as per the following file path structure:

    <yb_data_dir>/node-<node_number>/disk-<disk_number>/yb-data/tserver/data/rocksdb/table-<table_id>/[tablet-<tablet_id>.snapshots]/<snapshot_id>
    • <yb_data_dir> - a directory where YugabyteDB data is stored. The default value is ~/yugabyte-data.
    • <node_number> - used when multiple nodes are running on the same server (for testing, QA, and development). The default value is 1.
    • <disk_number> - used when running YugabyteDB on multiple disks with the --fs_data_dirs flag. The default value is 1.
    • <table_id> - the UUID of the table. You can obtain it from the http://<yb-master-ip>:7000/tables URL in the Admin UI.
    • <tablet_id> - each table contains a list of tablets. Each tablet has a <tablet_id>.snapshots directory that you need to copy.
    • <snapshot_id> - there is a directory for each snapshot, since you can have multiple completed snapshots on each server.

    This directory structure is specific to a local testing tool yb-ctl. In practice, for each server, you would use the --fs_data_dirs flag, which is a comma-separated list of paths for the data. It is recommended to have different paths on separate disks. In the yb-ctl example, these are the full paths up to the disk-number.

To obtain a snapshot of a multi-node cluster, you would access each node and copy the folders of only the leader tablets on that node. Since each tablet replica has a copy of the same data, there is no need to keep a copy for each replica.

If you don't want to keep the in-cluster snapshot, you can safely delete it.

Restore a snapshot from external storage

You can restore a snapshot that you have moved to external storage, as follows:

  1. Retrieve the snapshot metadata file from the external storage and apply it by running the import_snapshot command, as follows:

    ./bin/yb-admin -master_addresses <ip1:7100,ip2:7100,ip3:7100> import_snapshot my_keyspace.snapshot my_keyspace

    Notice that the following output contains the mapping between the old tablet IDs and the new tablet IDs:

    Read snapshot meta file my_keyspace.snapshot
Importing snapshot a9442525-c7a2-42c8-8d2e-658060028f0e (COMPLETE)
Table type: table
Target imported table name: test.t1
Table being imported: test.t1
Table type: table
Target imported table name: test.t2
Table being imported: test.t2
Successfully applied snapshot.
Object           Old ID                                 New ID
Keyspace         00004000000030008000000000000000       00004000000030008000000000000000
Table            00004000000030008000000000004003       00004000000030008000000000004001
Tablet 0         b0de9bc6a4cb46d4aaacf4a03bcaf6be       50046f422aa6450ca82538e919581048
Tablet 1         27ce76cade8e4894a4f7ffa154b33c3b       111ab9d046d449d995ee9759bf32e028
Snapshot         a9442525-c7a2-42c8-8d2e-658060028f0e   a9442525-c7a2-42c8-8d2e-658060028f0e

  2. Copy the tablet snapshots. Use the tablet mappings to copy the tablet snapshot files from the external location to an appropriate location, such as yb-data/tserver/data/rocksdb/table-<tableid>/tablet-<tabletid>.snapshots.

    Based on the preceding examples, you would execute the following commands:

    cp -r snapshot/tablet-b0de9bc6a4cb46d4aaacf4a03bcaf6be.snapshots/0d4b4935-2c95-4523-95ab-9ead1e95e794 \
      ~/yugabyte-data-restore/node-1/disk-1/yb-data/tserver/data/rocksdb/table-00004000000030008000000000004001/tablet-50046f422aa6450ca82538e919581048.snapshots/6beb9c0e-52ea-4f61-89bd-c160ec02c729

    cp -r snapshot/tablet-27ce76cade8e4894a4f7ffa154b33c3b.snapshots/0d4b4935-2c95-4523-95ab-9ead1e95e794 \
      ~/yugabyte-data-restore/node-1/disk-1/yb-data/tserver/data/rocksdb/table-00004000000030008000000000004001/tablet-111ab9d046d449d995ee9759bf32e028.snapshots/6beb9c0e-52ea-4f61-89bd-c160ec02c729

    For each tablet, you need to copy the snapshots folder on all tablet peers and in any configured read replica cluster.

  3. Restore the snapshot.

Note

YugabyteDB Anywhere provides an API and UI for backup and restore, automating most of the steps. You should use one or both, especially if you have many databases and snapshots to manage.