Cassandra管理之備份與恢復

Cassandra的備份就是對現有的數據做一個快照，恢復則是把快照進行還原。不僅可以對全庫做快照，也可以針對表、keyspace單獨做備份。另外它也支持增量備份。

1、全量備份

[root@db03 ~]# nodetool snapshot
Requested creating snapshot(s) for [all keyspaces] with snapshot name [1570691336948] and options {skipFlush=false}
Snapshot directory: 1570691336948

操作完成後，可以通過listsnapshots驗證，如下圖所示：

備份完成後，系統會在每個表所在的目錄下生成一個1570691336948文件夾，裏面存放了每個表的備份數據。這裏用rhnchecksum表進行說明，如下圖所示：

2、增量備份

默認情況下，它的增量備份是禁用的，可以通過以下命令進行驗證：

[root@db03 ~]# nodetool statusbackup
not running

啓用增量備份，命令如下：

[root@db03 ~]# nodetool enablebackup 
[root@db03 ~]# nodetool statusbackup 
running

執行下備份如下：

[root@db03 spacewalk]# nodetool snapshot
Requested creating snapshot(s) for [all keyspaces] with snapshot name [1570695931097] and options {skipFlush=false}
Snapshot directory: 1570695931097

3、恢復數據

cassandra的恢復過程如下:

• 清空表

cqlsh:spacewalk> select count(*) from rhnchecksum;           

 count
---------
 8404215

(1 rows)

Warnings :
Aggregation query used without partition key

cqlsh:spacewalk> truncate rhnchecksum;
cqlsh:spacewalk> select count(*) from rhnchecksum;

 count
-------
     0

(1 rows)

• 還原snapshot目錄的數據
  這裏將snapshot目錄的數據拷貝到數據目錄，然後執行refresh，如下：

  [root@db03 rhnchecksum-dbbb8330dde111e99dfb45c418aaa2bc]# pwd
  /var/lib/cassandra/data/spacewalk/rhnchecksum-dbbb8330dde111e99dfb45c418aaa2bc
  [root@db03 rhnchecksum-dbbb8330dde111e99dfb45c418aaa2bc]# cp -ra snapshots/1570695931097/* .
  --如果有索引數據也要進行拷貝操作
  [root@db03 rhnchecksum-dbbb8330dde111e99dfb45c418aaa2bc]# cp -ra snapshots/1570695931097/.rhnchecksum_idx/* .rhnchecksum_idx/

  當把快照文件複製到對應表的目錄下後，運行refresh命令加載新的SSTables 不需要重啓機器節點。

[root@db03 ~]# nodetool refresh spacewalk rhnchecksum
--完成後，cassandra的日誌會出現下面的提示:
[root@db03 ~]# tail -f /var/log/cassandra/system.log 
INFO  [RMI TCP Connection(68)-127.0.0.1] 2019-10-10 16:41:22,513 ColumnFamilyStore.java:734 - Loading new SSTables for spacewalk/rhnchecksum...
INFO  [RMI TCP Connection(68)-127.0.0.1] 2019-10-10 16:41:22,517 ColumnFamilyStore.java:782 - Renaming new SSTable /var/lib/cassandra/data/spacewalk/rhnchecksum-dbbb8330dde111e99dfb45c418aaa2bc/md-47-big to /var/lib/cassandra/data/spacewalk/rhnchecksum-dbbb8330dde111e99dfb45c418aaa2bc/md-50-big
INFO  [RMI TCP Connection(68)-127.0.0.1] 2019-10-10 16:41:22,548 ColumnFamilyStore.java:782 - Renaming new SSTable /var/lib/cassandra/data/spacewalk/rhnchecksum-dbbb8330dde111e99dfb45c418aaa2bc/md-49-big to /var/lib/cassandra/data/spacewalk/rhnchecksum-dbbb8330dde111e99dfb45c418aaa2bc/md-51-big
INFO  [RMI TCP Connection(68)-127.0.0.1] 2019-10-10 16:41:22,567 ColumnFamilyStore.java:782 - Renaming new SSTable /var/lib/cassandra/data/spacewalk/rhnchecksum-dbbb8330dde111e99dfb45c418aaa2bc/md-48-big to /var/lib/cassandra/data/spacewalk/rhnchecksum-dbbb8330dde111e99dfb45c418aaa2bc/md-52-big
INFO  [RMI TCP Connection(68)-127.0.0.1] 2019-10-10 16:41:22,589 ColumnFamilyStore.java:782 - Renaming new SSTable /var/lib/cassandra/data/spacewalk/rhnchecksum-dbbb8330dde111e99dfb45c418aaa2bc/md-46-big to /var/lib/cassandra/data/spacewalk/rhnchecksum-dbbb8330dde111e99dfb45c418aaa2bc/md-53-big
INFO  [RMI TCP Connection(68)-127.0.0.1] 2019-10-10 16:41:22,610 ColumnFamilyStore.java:817 - Loading new SSTables and building secondary indexes for spacewalk/rhnchecksum: [BigTableReader(path='/var/lib/cassandra/data/spacewalk/rhnchecksum-dbbb8330dde111e99dfb45c418aaa2bc/md-52-big-Data.db'), BigTableReader(path='/var/lib/cassandra/data/spacewalk/rhnchecksum-dbbb8330dde111e99dfb45c418aaa2bc/md-51-big-Data.db'), BigTableReader(path='/var/lib/cassandra/data/spacewalk/rhnchecksum-dbbb8330dde111e99dfb45c418aaa2bc/md-53-big-Data.db'), BigTableReader(path='/var/lib/cassandra/data/spacewalk/rhnchecksum-dbbb8330dde111e99dfb45c418aaa2bc/md-50-big-Data.db')]
INFO  [RMI TCP Connection(68)-127.0.0.1] 2019-10-10 16:41:22,614 SecondaryIndexManager.java:366 - Submitting index build of rhnchecksum_idx for data in BigTableReader(path='/var/lib/cassandra/data/spacewalk/rhnchecksum-dbbb8330dde111e99dfb45c418aaa2bc/md-52-big-Data.db'),BigTableReader(path='/var/lib/cassandra/data/spacewalk/rhnchecksum-dbbb8330dde111e99dfb45c418aaa2bc/md-51-big-Data.db'),BigTableReader(path='/var/lib/cassandra/data/spacewalk/rhnchecksum-dbbb8330dde111e99dfb45c418aaa2bc/md-53-big-Data.db'),BigTableReader(path='/var/lib/cassandra/data/spacewalk/rhnchecksum-dbbb8330dde111e99dfb45c418aaa2bc/md-50-big-Data.db')
INFO  [Service Thread] 2019-10-10 16:41:34,134 GCInspector.java:284 - ConcurrentMarkSweep GC in 467ms.  CMS Old Gen: 1227906720 -> 508200320; Code Cache: 35251328 -> 35276800; Metaspace: 45251080 -> 45251832; Par Eden Space: 6575264 -> 139631912; Par Survivor Space: 41943040 -> 14759936
INFO  [Service Thread] 2019-10-10 16:41:43,679 GCInspector.java:284 - ParNew GC in 236ms.  CMS Old Gen: 844136912 -> 967814552; Par Eden Space: 335544320 -> 0; Par Survivor Space: 35314704 -> 41943040
INFO  [RMI TCP Connection(68)-127.0.0.1] 2019-10-10 16:47:00,987 SecondaryIndexManager.java:386 - Index build of rhnchecksum_idx complete
INFO  [RMI TCP Connection(68)-127.0.0.1] 2019-10-10 16:47:00,987 ColumnFamilyStore.java:825 - Done loading load new SSTables for spacewalk/rhnchecksum

恢復完成後，驗證數據如下圖所示：

nodetool命令的選項中文解釋參考：Cassandra nodetool常用操作