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Percona Software for MongoDB Documentation

Point-in-time recovery

Version added: 1.3.0

Point-in-time recovery is restoring a database up to a specific timestamp. This includes restoring the data from a backup snapshot and replaying all events that occurred to this data up to a specified time from oplog slices.

Advantages Disadvantages
Helps you prevent data loss during a disaster such as a crashed database, accidental data deletion or drop of tables, and unwanted update of multiple fields instead of a single one. Restore takes longer since it requires you to restore the backup and then replay oplog events on top of it.

Enable point-in-time recovery

Set the pitr.enabled configuration option to true.

$ pbm config --set pitr.enabled=true

pitr:
  enabled: true

The pbm-agent starts saving consecutive slices of the oplog periodically. The pbm-agent to save oplog slices is randomly selected among the nodes according to their priority, whether it is the default or user-defined one.

You can manage the pbm-agent election by assigning a priority value to the mongod nodes. See the Adjust node priority for oplog slices for details.

Restore to a point-in-time

Oplog slicing

To start saving oplog slices, the following preconditions must be met:

  • A full backup snapshot is required. Starting with version 2.3.0, it can be a logical, a physical or an incremental backup. Make sure that a backup exists. See the Make a backup guide to make a backup snapshot.
  • Point-in-time recovery routine is enabled.

Point-in-time recovery routine is enabled.

If you just enabled point-in-time recovery, it requires 10 minutes for the first slice to appear in the pbm list output.

Important

For in MongoDB 5.0 and higher versions

If you reshard a collection, make a fresh backup and re-enable point-in-time recovery oplog slicing to prevent data inconsistency and restore failure.

For MongoDB 8.0 and higher versions

If you unshard a collection , make a fresh backup and re-enable point-in-time recovery oplog slicing to prevent data inconsistency and restore failure.

Starting with version 2.4.0, oplog slicing runs as follows:

  • Logical backups

    Before backup starts, the point-in-time recovery routine is automatically disabled. A backup routine creates oplog slices during the backup creation. After the backup is complete, the point-in-time recovery routine is re-enabled automatically. It copies the slices taken during the backup and continues oplog slicing from the latest timestamp.

  • Physical backups

    During a physical backup, the point-in-time recovery routine is not disabled and continues to save oplog slices in parallel with a backup snapshot operation.

Thus, if a backup snapshot is large and takes hours to make, all oplog events are saved for it, ensuring point-in-time recovery to any timestamp.

Oplog duration

Version added: 1.6.0

By default, a slice covers a 10-minute span of oplog events. It can be shorter if point-in-time recovery is disabled or interrupted by the start of a backup snapshot operation.

You can change the duration of an oplog span via the configuration file. Specify the new value (in minutes) for the pitr.oplogSpanMin option.

$ pbm config --set pitr.oplogSpanMin=5

pitr:
  oplogSpanMin: 5

If you set the new duration when the pbm-agent is making an oplog slice, the slice’s span is updated right away.

If the new duration is shorter, this triggers the pbm-agent to make a new slice with the updated span immediately. If the new duration is larger, the pbm-agent makes the next slice with the updated span in its scheduled time.

Adjust node priority for oplog slices

Version added: 2.6.0

Before version 2.6.0, the pbm-agent to save oplog slices is selected randomly across replica set members.

Starting with version 2.6.0, you can control from what node to save oplog slices by assigning the priority to the desired nodes via the configuration file. For example, you can ensure that both backups and oplog slices are taken from the nodes in a specific data center as defined in the organization’s regulations. Or, you can reduce network latency by making backups and / or oplog slices from nodes in geographically closest locations.

Node priority for oplog slices is handled similarly to the node priority for making backups, yet it is independent from it. Thus, you can assign a different priority for backups and oplog slices for the same node. Or, adjust only the priority for oplog slices, leaving the default one for backups.

PBM then handles both processes according to their priority.

The default node priority for oplog slices is the same as for making backups:

  • hidden node - priority 2
  • secondary nodes - priority 1
  • primary node - priority 0.5

To redefine it, specify the new priority for the pitr.priority option in the configuration file:

pitr:
  enabled: true
  priority:
    "rs1:27017": 1
    "rs2:27018": 2
    "rs3:27019": 1

The format of the priority array is <hostname:port>:<priority>.

Important

As soon as you adjust node priorities in the configuration file, it is assumed that you take manual control over them. The default rule to prefer secondary nodes over primary stops working.

To define priority in a sharded cluster, you can either list all nodes or specify priority for one node in each shard and config server replica set. The hostname and port uniquely identifies a node so that Percona Backup for MongoDB recognizes where it belongs to and grants the priority accordingly.

Note that if you listed only specific nodes, the remaining nodes will be automatically assigned priority 1.0. For example, you assigned priority 2.5 to only one secondary node in every shard and config server replica set of the sharded cluster.

pitr:
  enabled: true
  priority:
    "localhost:27027": 2.5  # config server replica set
    "localhost:27018": 2.5  # shard 1
    "localhost:28018": 2.5  # shard 2

The remaining secondaries and the primary nodes in the cluster receive priority 1.0.

To check the priorities, run the pbm status command with the --priority flag.

$ pbm status --priority
Sample output 
Cluster:
========
rs1:
  - rs1/rs101:27017 [S], Bkp Prio: [1.0], PITR Prio: [2.5]: pbm-agent [v2.7.0] OK
  - rs1/rs102:27017 [P], Bkp Prio: [0.5], PITR Prio: [2.0]: pbm-agent [v2.7.0] OK
  - rs1/rs103:27017 [S], Bkp Prio: [1.0], PITR Prio: [1.0]: pbm-agent [v2.7.0] OK

PBM saves oplog slices from the node with the highest priority. If this node is not responding, it selects the next priority node. If there are several nodes with the same priority, one of them is randomly elected for saving oplog slices.

Compressed oplog slices

Version added: 1.7.0

The oplog slices are saved with the s2 compression method by default. You can specify a different compression method via the configuration file. Specify the new value for the pitr.compression option.

$ pbm config --set pitr.compression=gzip

pitr:
  compression: gzip

Supported compression methods are: gzip, snappy, lz4, s2, pgzip, zstd.

Additionally, you can override the compression level used by the compression method by setting the pitr.compressionLevel option. The default values differ for each compression level.

Note that the higher value you specify, the more time and computing resources it will take to compress the data.

Note

You can use different compression methods for backup snapshots and point-in-time recovery slices. However, backup snapshot-related oplog is compressed with the same compression method as the backup itself.

View oplog slices

The oplog slices are stored in the pbmPitr subdirectory in the remote storage defined in the config. A slice name reflects the start and end time this slice covers.

The pbm list output includes the following information:

  • Backup snapshots. As of version 1.4.0, it also shows the completion time (renamed to the restore_to_time in version 2.0.0)
  • Valid time ranges for recovery
  • Point-in-time recovery status
$ pbm list

  2021-08-04T13:00:58Z [restore_to_time: 2021-08-04T13:01:23Z]
  2021-08-05T13:00:47Z [restore_to_time: 2021-08-05T13:01:11Z]
  2021-08-06T08:02:44Z [restore_to_time: 2021-08-06T08:03:09Z]
  2021-08-06T08:03:43Z [restore_to_time: 2021-08-06T08:04:08Z]
  2021-08-06T08:18:17Z [restore_to_time: 2021-08-06T08:18:41Z]

PITR <off>:
  2021-08-04T13:01:24 - 2021-08-05T13:00:11
  2021-08-06T08:03:10 - 2021-08-06T08:18:29
  2021-08-06T08:18:42 - 2021-08-06T08:33:09

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Last update: November 13, 2024
Created: November 13, 2024