Point In Time Recovery

Point in Time Recovery

Supported Databases

  • MySQL 5.7

Believed to work, but untested

  • MySQL 8.0

Introduction

The Point in Time Recovery feature in Vitess enables recovery of data to a specific point time (timestamp). There can be multiple recovery requests active at the same time. It is possible to recover across sharding actions, i.e. you can recover to a time when there were two shards even though at present there are four.

Point in Time Recovery leverages two Vitess features:

  1. The use of SNAPSHOT keyspaces for recovery of the last backup before a requested specific timestamp to restore to.
  2. Integration with a binlog server to allow vttablet to apply binary logs from the recovered backup up to the specified timestamp.

Use cases

  • Accidental deletion of data, e.g. dropping a table by mistake, running an UPDATE or DELETE with an incorrect WHERE clause, etc.
  • Corruption of data due to application bugs.
  • Corruption of data due to MySQL bugs or underlying hardware (e.g. storage) problems.

Preconditions

  • There should be a Vitess backup taken before the desired point in time.
  • There should be continuous binlogs available from the backup time to the desired point in time.
  • This feature is tested using Ripple as the binlog server. However, it should be possible to use a MySQL instance as source for the binlogs as well.

Example usage

To use this feature, you need a usable backup of Vitess data and continuous binlogs.

Here is how you can create a backup.

$ vtctlclient -server <vtctld_host>:<vtctld_port> Backup zone1-101

Here zone1-101 is the tablet alias of a replica tablet in the shard that you want to back up. Note that you can also use vtctlclient BackupShard to just specify a keyspace and shard, and have Vitess choose the tablet to run the backup for you, instead of having to specify the tablet alias explicitly.

To maintain continuous binlogs, you need to have a binlog server pointing to the master (or a replica, assuming that the replica is also maintaining its own binlogs, which is the default Vitess configuration). You can use Ripple as a binlog server, although there are other options; and you could use an existing MySQL server as well.

If you use Ripple, you will need to configure it yourself, and ensure you take care of the following:

  • You should have a highly available binlog server setup. If the binlog server goes down, you need to ensure that it is back up and able to synchronize the MySQL binary logs from its upstream MySQL server before the upstream server deletes the current binlog. If you do not do this, you will end up with gaps in your binlogs, which could make restoring to a specific point in time impossible. Make sure that you setup your operational and monitoring procedures accordingly.
  • The binlog files should be safely kept at some reliable and recoverable location (e.g. AWS S3, remote file storage).

Once the above is done, you can proceed with doing a recovery.

Recovery Procedure

First, you need to create a SNAPSHOT keyspace with a base_keyspace pointing to the original keyspace you are recovering the backup of. This can be done by using following:

$ vtctlclient -server <vtctld_host>:<vtctld_port> CreateKeyspace -keyspace_type=SNAPSHOT -base_keyspace=originalks -snapshot_time=2020-07-17T18:25:20Z restoreks

Here:

  • originalks is the base keyspace, i.e. the keyspace we took a backup of, and are trying to recover.
  • snapshot_time is the timestamp of the point in time to we want to recover to. Note the use of the Z in the timestamp, indicating it is expressed in UTC.
  • restoreks is the name of recovery keyspace, i.e. the keyspace to which we are restoring our backup.

Next, you can launch the vttablet, which as part of vttablet’s normal initialization procedure will look for a backup to restore. It will detect the meta-information you added on the keyspace topology node when creating the keyspace above. It will then use that information to restore the last backup earlier than the timestamp provided for the specific shard the vttablet is in.

Here are the command line arguments vttablet uses in this process. You may already be using some of these as part of your normal vttablet initialization parameters (e.g. if you are using the Vitess K8s operator):

  • -init_keyspace restoreks - here restoreks is the recovery keyspace name which we created earlier
  • -init_db_name_override vt_originalks - here vt_originalks is the name of the original underlying database for the keyspace that you backed up and want to restore. Usually, this takes the form of vt_ prepended to the keyspace name. However, the original underlying database could also have been using an -init_db_name_override directive of its own, and this value should then be set to match that.
  • -init_shard 0 - here 0 is the shard name (or range) which we want to recover.
  • -binlog_host x.x.x.x - hostname or IP address of binlog server.
  • -binlog_port XXXX - TCP port of binlog server.
  • -binlog_user XXXX - username to access binlog server.
  • -binlog_password YYYY - password to access binlog server.
  • -pitr_gtid_lookup_timeout duration - See below for details.

And then, depending on your backup storage implementation, you can use a variety of flags:

  • -backup_storage_implementation file - for plain file backup type. If you use this option, you will also need to specify:
    • -file_backup_storage_root - with a path pointing to your backup storage location.
  • -backup_storage_implementation s3 - for backing up to S3. If you use this option, you may need additional flags like:
    • -s3_backup_aws_region
    • -s3_backup_storage_bucket
    • -s3_backup_storage_root
  • There are more -backup_storage_implementation options like gcs and others.

You will also probably want to use other flags for backup and restore like:

  • -backup_engine_implementation xtrabackup - Use Percona Xtrabackup to take online backups. Without this flag, the mysql instance on the replica being backed up will be shut down during the backup.
  • -backup_storage_compress true - gzip compress the backup (default is true). You need to be consistent in your use of these flags for backup and restore.

Once the restore of the last backup earlier than the snapshot_time timestamp is completed, the vttablet proceeds to use the binlog_* parameters to connect to the binlog server and then apply all binlog events from the time of the backup until the timestamp provided.

Since the last backup for each shard making up the keyspace could be taken at different points in time, the amount of time that it takes to apply these events may differ between restores of different shards in the keyspace.

Note that to restore to the specified snapshot_time timestamp, vttablet needs to find the GTID corresponding to the last event before this timestamp from the binlog server. This is an expensive operation and may take some time. By default the timeout for this operation is one minute (1m). This can be changed by setting the vttablet -pitr_gtid_lookup_timeout flag.

VTGate will automatically exclude tablets belonging to snapshot keyspaces from query routing unless they are specifically addressed using USE restoreks or by using queries of the form SELECT ... FROM restoreks.table.

The base keyspace’s vschema will be copied over to the new snapshot keyspace as a default. If desired this can be overwritten by the user. Care needs to be taken to set require_explicit_routing to true when modifying a snapshot keyspace’s vschema, or you will bypass the VTGate routing safety feature described above.