cassandra - 将快照拍摄到不同的位置

Question

我想每隔 1 小时进行一次 Cassandra 备份并将其移动到共享位置。

Cassandra 在默认位置拍摄快照，如何在/opt/backup位置拍摄快照？

Answer 1

你不能（使用快照）。

nodetool snapshot -t <tag> <keyspace>是一个非常简单的工具 - 它只是为键空间数据目录中的每个文件创建硬链接到snapshots/<tag>.

由于这些是硬链接，因此它们必须位于同一文件系统上。这些硬链接的好处是快照速度非常快，并且最初不会消耗额外的磁盘空间（当 sstables 被压缩/删除时，文件仍保留在快照中）。

如果您希望在不同位置使用这些备份，请-t <tag>在创建快照时使用。我用demosnapshot一个简单的脚本制作了一个演示（没有完全阐述，但展示了这个想法：

$ cat cassandrabackup.sh
#!/bin/bash

TAG=`date +%Y%m%d%H%M%S`
BACKUP_LOC=/tmp/backup/`hostname`
KEYSPACE=demokeyspace

echo creating snapshot $TAG
nodetool snapshot -t $TAG $KEYSPACE

echo sync to backup location $BACKUP_LOC
find /var/lib/cassandra -type f -path "*snapshots/$TAG*" -printf %P\\0 | rsync -avP --files-from=- --from0 /var/lib/cassandra/ $BACKUP_LOC

echo removing snapshot $TAG
nodetool clearsnapshot -t $TAG

该脚本使用特定标签（日期时间）创建快照，将内容同步到备份位置，然后删除快照。如果KEYSPACE未定义，则备份所有键空间。

结果是这样的：

$ ./cassandrabackup.sh
creating snapshot 20170823132936
Requested creating snapshot(s) for [demokeyspace] with snapshot name [20170823132936] and options {skipFlush=false}
Snapshot directory: 20170823132936
sync to backup location /tmp/backup/host1.domain.tld
building file list ...
6 files to consider
data1/
data1/demokeyspace/
data1/demokeyspace/demotable-0bbb579087ef11e7aa786377cd3ba823/
data1/demokeyspace/demotable-0bbb579087ef11e7aa786377cd3ba823/snapshots/
data1/demokeyspace/demotable-0bbb579087ef11e7aa786377cd3ba823/snapshots/20170823132936/
data1/demokeyspace/demotable-0bbb579087ef11e7aa786377cd3ba823/snapshots/20170823132936/manifest.json
             13 100%    0.00kB/s    0:00:00 (xfr#1, to-chk=0/6)

sent 305 bytes  received 50 bytes  710.00 bytes/sec
total size is 13  speedup is 0.04
removing snapshot 20170823132936
Requested clearing snapshot(s) for [all keyspaces] with snapshot name [20170823132936]
$ ifjke@fsca01:~$ find /tmp/backup/
/tmp/backup/
/tmp/backup/host1.domain.tld
/tmp/backup/host1.domain.tld/data2
/tmp/backup/host1.domain.tld/data2/demokeyspace
/tmp/backup/host1.domain.tld/data2/demokeyspace/demotable-0bbb579087ef11e7aa786377cd3ba823
/tmp/backup/host1.domain.tld/data2/demokeyspace/demotable-0bbb579087ef11e7aa786377cd3ba823/snapshots
/tmp/backup/host1.domain.tld/data2/demokeyspace/demotable-0bbb579087ef11e7aa786377cd3ba823/snapshots/20170823125951
/tmp/backup/host1.domain.tld/data2/demokeyspace/demotable-0bbb579087ef11e7aa786377cd3ba823/snapshots/20170823125951/manifest.json
/tmp/backup/host1.domain.tld/data2/demokeyspace/demotable-0bbb579087ef11e7aa786377cd3ba823/snapshots/20170823130014
/tmp/backup/host1.domain.tld/data2/demokeyspace/demotable-0bbb579087ef11e7aa786377cd3ba823/snapshots/20170823130014/manifest.json
/tmp/backup/host1.domain.tld/data1
/tmp/backup/host1.domain.tld/data1/demokeyspace
/tmp/backup/host1.domain.tld/data1/demokeyspace/demotable-0bbb579087ef11e7aa786377cd3ba823
/tmp/backup/host1.domain.tld/data1/demokeyspace/demotable-0bbb579087ef11e7aa786377cd3ba823/snapshots
/tmp/backup/host1.domain.tld/data1/demokeyspace/demotable-0bbb579087ef11e7aa786377cd3ba823/snapshots/20170823132936
/tmp/backup/host1.domain.tld/data1/demokeyspace/demotable-0bbb579087ef11e7aa786377cd3ba823/snapshots/20170823132936/manifest.json
$

正如我过去自己犯过的那样 - 在备份中包含主机名；）

除此之外，cassandra 中还有一个增量备份功能：

http://docs.datastax.com/en/cassandra/3.0/cassandra/operations/opsBackupIncremental.html