大家都知道,Cassandra集群有复制功能,即使集群中的某个节点宕机,也可以防止数据丢失。但是,如果管理员不小心掉了一个数据量很大的表,而这个命令已经被集群中的所有副本执行了,这是否意味着你失去了这个表,无法恢复?有没有什么建议可以在短时间内应对这种灾难?
从cassandra 文件:
auto_snapshot (默认值:true) 启用或禁用是否在关键空间截断或丢表之前对数据进行快照。为了防止数据丢失,强烈建议使用默认设置。如果设置为false,则会在截断或删除表时丢失数据。
如果管理员已经将数据删除并复制到所有节点中,如果没有一致的备份,很难恢复数据。
也许考虑到cassandra中的删除不是即时执行的,你可以恢复数据。当你删除数据的时候,cassandra会用一个墓碑来替换数据,然后这个墓碑可以传播到错过初始删除请求的副本中。
参见 http:/wiki.apache.orgcassandraDistributedDeletes。
标有墓碑的列在配置的时间段内存在(由列族上设置的gc_grace_seconds值定义),然后在时间结束后被压实过程永久删除。默认值是10天。
按照在 关于删除 也许如果你关闭一些节点,等到压实成功,数据完全从SSTables中删除,然后再次打开节点,数据就会再次出现。但这只有在你不对节点进行周期性的修复操作时才会发生。
我从来没有尝试过这个问题,这只是我看cassandra文档时的一个想法。
第1步:我使用下面的命令创建了一个表。
CREATE TABLE Cricket (
PlayerID uuid,
LastName varchar,
FirstName varchar,
City varchar,
State varchar,
PRIMARY KEY (PlayerID));
步骤-2:使用以下命令插入3条记录。
INSERT INTO Cricket (PlayerID, LastName, FirstName, City, State)
VALUES (now(), 'Pendulkar', 'Sachin', 'Mumbai','Maharastra');
INSERT INTO Cricket (PlayerID, LastName, FirstName, City, State)
VALUES (now(), 'Vholi', 'Virat', 'Delhi','New Delhi');
INSERT INTO Cricket (PlayerID, LastName, FirstName, City, State)
VALUES (now(), 'Sharma', 'Rohit', 'Berhampur','Odisha');
步骤-3:我不小心删除了Cricket表。
drop table Cricket;
步骤-4:需要通过使用自动快照备份恢复该表 注:auto_snapshot (默认值:true ) 启用或禁用是否在截断键空间或丢表之前对数据进行快照。为了防止数据丢失,强烈建议使用默认设置。
步骤-5:查找快照的位置和文件
cassandra@node1:~/data/students_details$ cd cricket-88128dc0960d11ea947b39646348bb4f
cassandra@node1:~/data/students_details/cricket-88128dc0960d11ea947b39646348bb4f$ ls -lrth
total 0
drwxrwxr-x 2 cassandra cassandra 6 May 14 18:05 backups
drwxrwxr-x 3 cassandra cassandra 43 May 14 18:06 snapshots
Step-6: You will get one .cql file in that snapshot location which having tables DDL.
cassandra@node1:~/data/students_details/cricket-88128dc0960d11ea947b39646348bb4f/snapshots/dropped-1589479603749-cricket$ ls -lrth
total 44K
-rw-rw-r-- 1 cassandra cassandra 92 May 14 18:06 md-1-big-Summary.db
-rw-rw-r-- 1 cassandra cassandra 61 May 14 18:06 md-1-big-Index.db
-rw-rw-r-- 1 cassandra cassandra 16 May 14 18:06 md-1-big-Filter.db
-rw-rw-r-- 1 cassandra cassandra 179 May 14 18:06 md-1-big-Data.db
-rw-rw-r-- 1 cassandra cassandra 92 May 14 18:06 md-1-big-TOC.txt
-rw-rw-r-- 1 cassandra cassandra 4.7K May 14 18:06 md-1-big-Statistics.db
-rw-rw-r-- 1 cassandra cassandra 9 May 14 18:06 md-1-big-Digest.crc32
-rw-rw-r-- 1 cassandra cassandra 43 May 14 18:06 md-1-big-CompressionInfo.db
-rw-rw-r-- 1 cassandra cassandra 891 May 14 18:06 schema.cql
-rw-rw-r-- 1 cassandra cassandra 31 May 14 18:06 manifest.json
cassandra@node1:~/data/students_details/cricket-88128dc0960d11ea947b39646348bb4f/snapshots/dropped-1589479603749-cricket$
more schema.cql
cassandra@node1:~/data/students_details/cricket-88128dc0960d11ea947b39646348bb4f/snapshots/dropped-1589479603749-cricket$ more schema.cql
CREATE TABLE IF NOT EXISTS students_details.cricket (
playerid uuid PRIMARY KEY,
city text,
firstname text,
lastname text,
state text)
WITH ID = 88128dc0-960d-11ea-947b-39646348bb4f
AND bloom_filter_fp_chance = 0.01
AND dclocal_read_repair_chance = 0.1
AND crc_check_chance = 1.0
AND default_time_to_live = 0
AND gc_grace_seconds = 864000
AND min_index_interval = 128
AND max_index_interval = 2048
AND memtable_flush_period_in_ms = 0
AND read_repair_chance = 0.0
AND speculative_retry = '99PERCENTILE'
AND comment = ''
AND caching = { 'keys': 'ALL', 'rows_per_partition': 'NONE' }
AND compaction = { 'max_threshold': '32', 'min_threshold': '4', 'class': 'org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy' }
AND compression = { 'chunk_length_in_kb': '64', 'class': 'org.apache.cassandra.io.compress.LZ4Compressor' }
AND cdc = false
AND extensions = { };
步骤-7:登录数据库,使用该DDL创建表。
apiadmin@cqlsh:coopersdev> use students_details;
apiadmin@cqlsh:students_details> CREATE TABLE IF NOT EXISTS students_details.cricket (
... playerid uuid PRIMARY KEY,
... city text,
... firstname text,
... lastname text,
... state text)
... WITH ID = 88128dc0-960d-11ea-947b-39646348bb4f
... AND bloom_filter_fp_chance = 0.01
... AND dclocal_read_repair_chance = 0.1
... AND crc_check_chance = 1.0
... AND default_time_to_live = 0
... AND gc_grace_seconds = 864000
... AND min_index_interval = 128
... AND max_index_interval = 2048
... AND memtable_flush_period_in_ms = 0
... AND read_repair_chance = 0.0
... AND speculative_retry = '99PERCENTILE'
... AND comment = ''
... AND caching = { 'keys': 'ALL', 'rows_per_partition': 'NONE' }
... AND compaction = { 'max_threshold': '32', 'min_threshold': '4', 'class': 'org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy' }
... AND compression = { 'chunk_length_in_kb': '64', 'class': 'org.apache.cassandra.io.compress.LZ4Compressor' }
... AND cdc = false
... AND extensions = { };
apiadmin@cqlsh:students_details>
第8步:将快照文件夹中的所有文件复制到现有的Cricket表文件夹中。
cassandra@node1:~/data/students_details/cricket-88128dc0960d11ea947b39646348bb4f/snapshots/dropped-1589479603749-cricket$ pwd
/home/cassandra/data/students_details/cricket-88128dc0960d11ea947b39646348bb4f/snapshots/dropped-1589479603749-cricket
cassandra@node1:~/data/students_details/cricket-88128dc0960d11ea947b39646348bb4f/snapshots/dropped-1589479603749-cricket$ cp * /home/cassandra/data/students_details/cricket-88128dc0960d11ea947b39646348bb4f
cassandra@node1:~/data/students_details/cricket-88128dc0960d11ea947b39646348bb4f/snapshots/dropped-1589479603749-cricket$ cd /home/cassandra/data/students_details/cricket-88128dc0960d11ea947b39646348bb4f
cassandra@node1:~/data/students_details/cricket-88128dc0960d11ea947b39646348bb4f$ ls -lrth
total 44K
drwxrwxr-x 2 cassandra cassandra 6 May 14 18:05 backups
drwxrwxr-x 3 cassandra cassandra 43 May 14 18:06 snapshots
-rw-rw-r-- 1 cassandra cassandra 891 May 14 18:11 schema.cql
-rw-rw-r-- 1 cassandra cassandra 92 May 14 18:11 md-1-big-TOC.txt
-rw-rw-r-- 1 cassandra cassandra 92 May 14 18:11 md-1-big-Summary.db
-rw-rw-r-- 1 cassandra cassandra 4.7K May 14 18:11 md-1-big-Statistics.db
-rw-rw-r-- 1 cassandra cassandra 61 May 14 18:11 md-1-big-Index.db
-rw-rw-r-- 1 cassandra cassandra 16 May 14 18:11 md-1-big-Filter.db
-rw-rw-r-- 1 cassandra cassandra 9 May 14 18:11 md-1-big-Digest.crc32
-rw-rw-r-- 1 cassandra cassandra 179 May 14 18:11 md-1-big-Data.db
-rw-rw-r-- 1 cassandra cassandra 43 May 14 18:11 md-1-big-CompressionInfo.db
-rw-rw-r-- 1 cassandra cassandra 31 May 14 18:11 manifest.json
cassandra@node1:~/data/students_details/cricket-88128dc0960d11ea947b39646348bb4f$
步骤-9: 使用下面的命令,开始使用sstableloader恢复表的数据
cassandra@node1:~$ sstableloader -d 10.213.61.21 -username cassandra --password cassandra /home/cassandra/data/students_details/cricket-d3576f60960f11ea947b39646348bb4f/snapshots
Established connection to initial hosts
Opening sstables and calculating sections to stream
Summary statistics:
Connections per host : 1
Total files transferred : 0
Total bytes transferred : 0.000KiB
Total duration : 2920 ms
Average transfer rate : 0.000KiB/s
Peak transfer rate : 0.000KiB/s
步骤-10:表格恢复成功,请验证。
playerid | city | firstname | lastname | state
--------------------------------------+-----------+-----------+-----------+------------
d7b12c90-960f-11ea-947b-39646348bb4f | Berhampur | Rohit | Sharma | Odisha
d7594890-960f-11ea-947b-39646348bb4f | Delhi | Virat | Vholi | New Delhi
d7588540-960f-11ea-947b-39646348bb4f | Mumbai | Sachin | Pendulkar | Maharastra