Backup and Restore
Contents
Backup and Restore#
High Availability Description#
The nameserver nodes cannot all fail. Failover and recovery cannot be done if all fail.
High availability is not guaranteed in the case of no secondary replica
In the case of two replicas and two nodes, only one node of tablet can fail.
In the case of two replicas and multiple nodes, the two tablet nodes where the same partition is located cannot fail at the same time.
In the case of three replicas and three nodes, a tablet failure node can automatically perform failover and data recovery. Failure of two tablet nodes does not guarantee automatic failover and data recovery, but reads and writes can return to normal within minutes.
In the case of three replicas and multiple nodes, if the two tablets where the same partition is located hangs, the automatic failover and data recovery of the partition are not guaranteed, but the read and write can return to normal within minutes.
If there is a leader partition in the failed node and there is always write traffic, a small amount of data may be lost.
Downtime and Recovery#
OpenMLDB high availability can be configured in automatic mode and manual mode. In automatic mode, if the node fails and recovers, the system will automatically perform failover and data recovery, otherwise manual processing is required
The mode can be switched by modifying the auto_failover configuration. The default is to open the automatic mode. You can get the configuration status and modify the configuration in the following ways
$ ./bin/openmldb --zk_cluster=172.27.128.31:8090,172.27.128.32:8090,172.27.128.33:8090 --zk_root_path=/openmldb_cluster --role=ns_client
> confget
key value
-----------------------------
auto_failover true
> confset auto_failover false
set auto_failover ok
>confget
key value
-----------------------------
auto_failover false
**When auto_failover is enabled, if a node goes offline, the is_alive status of the showtable command will change to no. If the node contains a leader of a partition, the partition will re-select the leader. **
$ ./bin/openmldb --zk_cluster=172.27.128.31:8090,172.27.128.32:8090,172.27.128.33:8090 --zk_root_path=/openmldb_cluster --role=ns_client
> showtable
name tid pid endpoint role ttl is_alive compress_type offset record_cnt memused
----------------------------------------------------------------------------------------------------------------------
flow 4 0 172.27.128.32:8541 leader 0min no kNoCompress 0 0 0.000
flow 4 0 172.27.128.33:8541 follower 0min yes kNoCompress 0 0 0.000
flow 4 0 172.27.128.31:8541 leader 0min yes kNoCompress 0 0 0.000
flow 4 1 172.27.128.33:8541 leader 0min yes kNoCompress 0 0 0.000
flow 4 1 172.27.128.31:8541 follower 0min yes kNoCompress 0 0 0.000
flow 4 1 172.27.128.32:8541 follower 0min no kNoCompress 0 0 0.000
When auto_failover is turned off, manual operations are required for node offline and recovery. There are two commands offlineendpoint and recoverendpoint
If the node fails, you need to execute offlineendpoint to offline the node
Command format: offlineendpoint endpoint
endpoint is the endpoint of the failed node. This command will offline the node and perform the following operations on all partitions under the node:
If it is the leader, execute the re-election of the leader
If it is a follower, find the leader and delete the current endpoint replica from the leader
$ ./bin/openmldb --zk_cluster=172.27.128.31:8090,172.27.128.32:8090,172.27.128.33:8090 --zk_root_path=/openmldb_cluster --role=ns_client
> showtablet
endpoint state age
-------------------------------------------
172.27.128.31:8541 kTabletHealthy 3h
172.27.128.32:8541 kTabletOffline 7m
172.27.128.33:8541 kTabletHealthy 3h
> offlineendpoint 172.27.128.32:8541
offline endpoint ok
>showtable
name tid pid endpoint role ttl is_alive compress_type offset record_cnt memused
----------------------------------------------------------------------------------------------------------------------
flow 4 0 172.27.128.32:8541 leader 0min no kNoCompress 0 0 0.000
flow 4 0 172.27.128.33:8541 follower 0min yes kNoCompress 0 0 0.000
flow 4 0 172.27.128.31:8541 leader 0min yes kNoCompress 0 0 0.000
flow 4 1 172.27.128.33:8541 leader 0min yes kNoCompress 0 0 0.000
flow 4 1 172.27.128.31:8541 follower 0min yes kNoCompress 0 0 0.000
flow 4 1 172.27.128.32:8541 follower 0min no kNoCompress 0 0 0.000
After executing offlineendpoint, each partition will be assigned a new leader. If a partition fails to execute, you can execute changeleader on this partition alone. The command format is: changeleader table_name pid
If the node has recovered, you can execute recoverendpoint to recover the data
Command format: recoverendpoint endpoint
endpoint is the endpoint of the node whose status has changed to healthy
$ ./bin/openmldb --zk_cluster=172.27.128.31:8090,172.27.128.32:8090,172.27.128.33:8090 --zk_root_path=/openmldb_cluster --role=ns_client
> showtablet
endpoint state age
-------------------------------------------
172.27.128.31:8541 kTabletHealthy 3h
172.27.128.32:8541 kTabletHealthy 7m
172.27.128.33:8541 kTabletHealthy 3h
> recoverendpoint 172.27.128.32:8541
recover endpoint ok
> showopstatus
op_id op_type name pid status start_time execute_time end_time cur_task
-----------------------------------------------------------------------------------------------------------
54 kUpdateTableAliveOP flow 0 kDone 20180824195838 2s 20180824195840 -
55 kChangeLeaderOP flow 0 kDone 20180824200135 0s 20180824200135 -
56 kOfflineReplicaOP flow 1 kDone 20180824200135 1s 20180824200136 -
57 kUpdateTableAliveOP flow 0 kDone 20180824200212 0s 20180824200212 -
58 kRecoverTableOP flow 0 kDone 20180824200623 1s 20180824200624 -
59 kRecoverTableOP flow 1 kDone 20180824200623 1s 20180824200624 -
60 kReAddReplicaOP flow 0 kDoing 20180824200624 4s - kLoadTable
61 kReAddReplicaOP flow 1 kDoing 20180824200624 4s - kLoadTable
Execute showopstatus to view the running progress of the task. If the status is in the doing state, the task has not been completed.
$ ./bin/openmldb --zk_cluster=172.27.128.31:8090,172.27.128.32:8090,172.27.128.33:8090 --zk_root_path=/openmldb_cluster --role=ns_client
> showopstatus
op_id op_type name pid status start_time execute_time end_time cur_task
---------------------------------------------------------------------------------------------------------
54 kUpdateTableAliveOP flow 0 kDone 20180824195838 2s 20180824195840 -
55 kChangeLeaderOP flow 0 kDone 20180824200135 0s 20180824200135 -
56 kOfflineReplicaOP flow 1 kDone 20180824200135 1s 20180824200136 -
57 kUpdateTableAliveOP flow 0 kDone 20180824200212 0s 20180824200212 -
58 kRecoverTableOP flow 0 kDone 20180824200623 1s 20180824200624 -
59 kRecoverTableOP flow 1 kDone 20180824200623 1s 20180824200624 -
60 kReAddReplicaOP flow 0 kDone 20180824200624 9s 20180824200633 -
61 kReAddReplicaOP flow 1 kDone 20180824200624 9s 20180824200633 -
> showtable
>showtable
name tid pid endpoint role ttl is_alive compress_type offset record_cnt memused
----------------------------------------------------------------------------------------------------------------------
flow 4 0 172.27.128.32:8541 follower 0min yes kNoCompress 0 0 0.000
flow 4 0 172.27.128.33:8541 follower 0min yes kNoCompress 0 0 0.000
flow 4 0 172.27.128.31:8541 leader 0min yes kNoCompress 0 0 0.000
flow 4 1 172.27.128.33:8541 leader 0min yes kNoCompress 0 0 0.000
flow 4 1 172.27.128.31:8541 follower 0min yes kNoCompress 0 0 0.000
flow 4 1 172.27.128.32:8541 follower 0min yes kNoCompress 0 0 0.000
If showtable turns to yes, it means that the recovery has been successful. If some partitions fail to recover, you can execute recovertable separately. The command format is: recovertable table_name pid endpoint
Note: offlineendpoint must be executed once before recoverendpoint is executed
One-click recovery#
If the cluster is restarted after being offline at the same time, autofailover cannot automatically restore data, and a one-click recovery script needs to be executed.
Steps:#
Modify env.sh in the tools directory of the openmldb package. There are 3 parameters in the configuration file
openmldb_bin_path specifies the openmldb bin path
zk_cluster specifies the address of the zk cluster
zk_root_path specifies the address of the zk root path
Execute ./recoverdata.sh
Log in to ns_client, and showopstatus to check the execution progress of related ops.
Manual data recovery#
Applicable scenario: The nodes where all replicas of a partition are located are down.
1 Start the process of each node#
2 Turn off autofailover#
Execute the confset command on the ns client
confset auto_failover false
3 Recover data#
When restoring data manually, it is necessary to restore the data partition by partition. The recovery steps are as follows:
Execute showtable table name with ns client
Modify the table partition alive status to no, execute it with nsclient. updatetablealive table_name pid endppoint is_alive
updatetablealive t1 * 172.27.2.52:9991 no
Perform the following steps for each partition in the table:
Restore the leader. If there are multiple leaders, choose the one with the larger offset
Use the tablet client to connect to the node where the leader is located, and execute the loadtable command. loadtable tablename tid pid ttl seg_cnt, seg_cnt is 8
loadtable test 1 1 144000 8
To check the load progress, execute gettablestatus to check the load progress. gettablestatus tid pid. Wait for stat to change from TableLoading state to TableNormal state
gettablestatus 1 1
Modify the leader alive status to yes. Execute with nsclient
updatetablealive table_name pid 172.27.2.52:9991 yes
Use recovertable other replicas, execute recovertable table_name pid endpoint with nsclient
recovertable table1 1 172.27.128.31:9527
4 Restore autofailover#
Execute the confset command on the ns client
confset auto_failover true