Cassandra管理之备份与恢复

Cassandra的备份就是对现有的数据做一个快照，恢复则是把快照进行还原。不仅可以对全库做快照，也可以针对表、keyspace单独做备份。另外它也支持增量备份。

1、全量备份

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

操作完成后，可以通过listsnapshots验证，如下图所示：

备份完成后，系统会在每个表所在的目录下生成一个1570691336948文件夹，里面存放了每个表的备份数据。这里用rhnchecksum表进行说明，如下图所示：

2、增量备份

默认情况下，它的增量备份是禁用的，可以通过以下命令进行验证：

[root@db03 ~]# nodetool statusbackup
not running

启用增量备份，命令如下：

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

执行下备份如下：

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

3、恢复数据

cassandra的恢复过程如下:

• 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)

• 还原snapshot目录的数据
  这里将snapshot目录的数据拷贝到数据目录，然后执行refresh，如下：

  [root@db03 rhnchecksum-dbbb8330dde111e99dfb45c418aaa2bc]# pwd
  /var/lib/cassandra/data/spacewalk/rhnchecksum-dbbb8330dde111e99dfb45c418aaa2bc
  [root@db03 rhnchecksum-dbbb8330dde111e99dfb45c418aaa2bc]# cp -ra snapshots/1570695931097/* .
  --如果有索引数据也要进行拷贝操作
  [root@db03 rhnchecksum-dbbb8330dde111e99dfb45c418aaa2bc]# cp -ra snapshots/1570695931097/.rhnchecksum_idx/* .rhnchecksum_idx/

  当把快照文件复制到对应表的目录下后，运行refresh命令加载新的SSTables 不需要重启机器节点。

[root@db03 ~]# nodetool refresh spacewalk rhnchecksum
--完成后，cassandra的日志会出现下面的提示:
[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

恢复完成后，验证数据如下图所示：

nodetool命令的选项中文解释参考：Cassandra nodetool常用操作