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Create a backup and restore guide #148

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Jan 26, 2021
Merged

Create a backup and restore guide #148

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8c44cc4
update backup and restore guide
feeblefakie Jan 25, 2021
4e470aa
update
feeblefakie Jan 25, 2021
635e688
fix (#149)
feeblefakie Jan 26, 2021
af50173
Merge branch 'master' into backup-doc
feeblefakie Jan 26, 2021
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2 changes: 1 addition & 1 deletion .circleci/config.yml
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Expand Up @@ -47,7 +47,7 @@ jobs:
# We need to edit DEFAULT_CQLVER defined in the cqlsh script
# to connect to the server without --cqlversion command line option
command: |
curl -O https://bootstrap.pypa.io/get-pip.py
curl -O https://bootstrap.pypa.io/2.7/get-pip.py
sudo python get-pip.py
sudo pip install cqlsh
sudo sed -i "s/^DEFAULT_CQLVER = .*/DEFAULT_CQLVER = '3.4.4'/" /usr/local/bin/cqlsh
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17 changes: 17 additions & 0 deletions docs/backup-restore.md
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# A Guide on How to Back up and Restore Databases Integrated with Scalar DB

Since Scalar DB provides transaction capability on top of non-transactional (possibly transactional) databases non-invasively, you need to take special care of backing up and restoring the databases in a transactionally-consistent way.
This document sets out some guidelines for backing up and restoring the databases that Scalar DB supports.

## Cassandra

Since Cassandra has a built-in replication mechanism, we don't always need a transactionally-consistent backup to recover a Cassandra cluster.

For example, if replication is properly set to 3 and only the data of one of the nodes in a cluster is lost, we don't need a transactionally-consistent backup because the node can be recovered with a normal (transactionally-inconsistent) snapshot and the repair mechanism.
However, if the quorum of nodes of a cluster loses their data, we need a transactionally-consistent backup to restore the cluster to a certain transactionally-consistent point.

The easiest way to take a transactionally-consistent backup for Scalar DB on Cassandra is to use [Cassy](https://github.com/scalar-labs/cassy).
Cassy takes snapshots of a Cassandra cluster after it pauses the application cluster to make the resulting snapshots transactionally-consistent.
Please see [the doc](https://github.com/scalar-labs/cassy/blob/master/docs/getting-started.md#take-cluster-wide-consistent-backups) for more details.

Note that we can simply use the snapshots when restoring a cluster because they are just snapshots of Cassandra. In any case, it is recommended to use Cassy for restoration as well to minimize operational mistakes.
1 change: 1 addition & 0 deletions docs/getting-started-with-scalardb.md
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Expand Up @@ -280,3 +280,4 @@ These are just simple examples of how Scalar DB is used. For more information, p
* [Javadoc](https://scalar-labs.github.io/scalardb/javadoc/)
* [Database schema in Scalar DB](schema.md)
* [Schema tool](../tools/scalar-schema/README.md)
* [How to Back up and Restore](backup-restore.md)