故障分析 | cassandra 集群数据故障转移

作者:杨文

DBA,负责客户项目的需求与维护,会点数据库,不限于MySQL、Redis、Cassandra、GreenPlum、ClickHouse、Elastic、TDSQL等等。

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一、前情提要:

我们知道 cassandra 具有分区容错性和强一致性,但是当数据所在主机发生故障时,该主机对应的数据副本该何去何从呢?是否跟宿主机一样变得不可用呢?想知道答案的话,就跟我一起往下看吧。

二、实验环境:

集群模式下跨数据中心:

数据中心 节点IP 种子节点
DC1 10.186.60.61、10.186.60.7、10.186.60.118、10.186.60.67 10.186.60.61、10.186.60.7
DC2 10.186.60.53、10.186.60.65、10.186.60.94、10.186.60.68 10.186.60.53、10.186.60.65

首先一起来瞅一瞅节点加入集群过程中的 owns 变化:

[cassandra@data01 ~]$ nodetool status
Datacenter: dc1
=================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
--  Address        Load       Tokens  Owns (effective)  Host ID                               Rack
UN  10.186.60.7    88.29 KiB  16      46.0%             4702178e-9878-48dc-97e7-9211b7c9f2e7  rack1
UN  10.186.60.118  69.07 KiB  16      37.7%             c920c611-2e8b-472d-93a4-34f1abd5b207  rack1
UN  10.186.60.61   88.25 KiB  16      34.2%             af2e0c42-3a94-4647-9716-c484b690899i  rack1

Datacenter: dc2
=================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
--  Address        Load       Tokens  Owns (effective)  Host ID                               Rack
UN  10.186.60.65   69.04 KiB  16      41.4%             89683bf8-aff8-4fdc-9525-c14764cf2d4f  rack2
UN  10.186.60.53   83.18 KiB  16      41.7%             7c91c707-abac-44f2-811O-b18f03f03d13  rack2

[cassandra@data01 ~]$ nodetool status
Datacenter: dc1
=================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
--  Address        Load       Tokens  Owns (effective)  Host ID                               Rack
UN  10.186.60.67   74.01 KiB  16      24.7%             9d6d759b-c00c-488b-938d-3e1ef9b92b02  rack1
UN  10.186.60.7    88.29 KiB  16      27.5%             4702178e-9878-48dc-97e7-9211b7c9f2e7  rack1
UN  10.186.60.118  83.16 KiB  16      28.9%             c920c611-2e8b-472d-93a4-34f1abd5b207  rack1
UN  10.186.60.61   88.25 KiB  16      30.3%             af2e0c42-3a94-4647-9716-c484b690899i  rack1

Datacenter: dc2
=================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
--  Address        Load       Tokens  Owns (effective)  Host ID                               Rack
UN  10.186.60.65   83.17 KiB  16      27.7%             89683bf8-aff8-4fdc-9525-c14764cf2d4f  rack2
UN  10.186.60.53   83.18 KiB  16      29.8%             7c91c707-abac-44f2-811O-b18f03f03d13  rack2
UN  10.186.60.94   69.05 KiB  16      31.1%             c8fa86e4-ee9a-4c62-b00b-d15edc967b9f  rack2

[cassandra@data01 ~]$ nodetool status
Datacenter: dc1
=================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
--  Address        Load       Tokens  Owns (effective)  Host ID                               Rack
UN  10.186.60.67   74.01 KiB  16      21.4%             9d6d759b-c00c-488b-938d-3e1ef9b92b02  rack1
UN  10.186.60.7    88.29 KiB  16      25.2%             4702178e-9878-48dc-97e7-9211b7c9f2e7  rack1
UN  10.186.60.118  83.16 KiB  16      27.1%             c920c611-2e8b-472d-93a4-34f1abd5b207  rack1
UN  10.186.60.61   83.19 KiB  16      28.9%             af2e0c42-3a94-4647-9716-c484b690899i  rack1

Datacenter: dc2
=================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
--  Address        Load       Tokens  Owns (effective)  Host ID                               Rack
UN  10.186.60.68   88.55 KiB  16      21.6%             a7307228-62bb-4354-9853-990cac9614ab  rack2
UN  10.186.60.65   83.17 KiB  16      24.0%             89683bf8-aff8-4fdc-9525-c14764cf2d4f  rack2
UN  10.186.60.53   83.18 KiB  16      25.4%             7c91c707-abac-44f2-811O-b18f03f03d13  rack2
UN  10.186.60.94   69.05 KiB  16      26.4%             c8fa86e4-ee9a-4c62-b00b-d15edc967b9f  rack2

可以看到,刚建立的集群,owns 的总和时刻保持在 200% ,但单个数据中心的 owns 不是 100% 。

三、具体实验:

3.1、实验1:

[cassandra@data01 ~]$ cqlsh 10.186.60.61 -u cassandra -p cassandra
CREATE KEYSPACE "dcdatabase" WITH REPLICATION = {'class':'NetworkTopologyStrategy', 'dc1' : 4, 'dc2' : 4};
use dcdatabase;
create table test (id int, user_name varchar, primary key (id) );
insert into test (id,name) VALUES (1,'test1');
insert into test (id,name) VALUES (2,'test2');
insert into test (id,name) VALUES (3,'test3');
insert into test (id,name) VALUES (4,'test4');
insert into test (id,name) VALUES (5,'test5');

查看集群状态:

[cassandra@data01 ~]$ nodetool status
Datacenter: dc1
=================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
--  Address        Load       Tokens  owns (effective)  Host ID                               Rack
UN  10.186.60.67   96.55 KiB  16      100.0%            9d6d759b-c00c-488b-938d-3e1ef9b92b02  rack1
UN  10.186.60.7    88.29 KiB  16      100.0%            4702178e-9878-48dc-97e7-9211b7c9f2e7  rack1
UN  10.186.60.118  88.33 KiB  16      100.0%            c920c611-2e8b-472d-93a4-34f1abd5b207  rack1
UN  10.186.60.61   88.37 KiB  16      100.0%            af2e0c42-3a94-4647-9716-c484b690899i  rack1

Datacenter: dc2
=================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
--  Address        Load       Tokens  owns (effective)  Host ID                               Rack
UN  10.186.60.68   74.23 KiB  16      100.0%            a7307228-62bb-4354-9853-990cac9614ab  rack2
UN  10.186.60.65   83.17 KiB  16      100.0%            89683bf8-aff8-4fdc-9525-c14764cf2d4f  rack2
UN  10.186.60.53   88.36 KiB  16      100.0%            7c91c707-abac-44f2-811O-b18f03f03d13  rack2
UN  10.186.60.94   74.23 KiB  16      100.0%            c8fa86e4-ee9a-4c62-b00b-d15edc967b9f  rack2

可以看到集群中,每个数据中心的 owns 都是 400% ,符合四副本的设置;

查看数据在节点上的分布情况:

[cassandra@data01 ~]$ nodetool getendpoints dcdatabase test 1
10.186.60.7
10.186.60.94
10.186.60.65
10.186.60.118
10.186.60.67
10.186.60.61
10.186.60.53
10.186.60.68
[cassandra@data03 ~]$ nodetool getendpoints dcdatabase test 5
10.186.60.67
10.186.60.94
10.186.60.7
10.186.60.53
10.186.60.65
10.186.60.118
10.186.60.61
10.186.60.68

可以看到集群数据分布在所有数据中心的所有节点上,符合数据的分布原理。

测试并查看集群中出现故障节点后的数据分布情况:

94机器关闭服务:systemctl stop cassandra

[cassandra@data01 ~]$ nodetool status
Datacenter: dc1
=================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
--  Address        Load       Tokens  owns (effective)  Host ID                               Rack
UN  10.186.60.67   96.55 KiB  16      100.0%            9d6d759b-c00c-488b-938d-3e1ef9b92b02  rack1
UN  10.186.60.7    88.29 KiB  16      100.0%            4702178e-9878-48dc-97e7-9211b7c9f2e7  rack1
UN  10.186.60.118  88.33 KiB  16      100.0%            c920c611-2e8b-472d-93a4-34f1abd5b207  rack1
UN  10.186.60.61   88.37 KiB  16      100.0%            af2e0c42-3a94-4647-9716-c484b690899i  rack1

Datacenter: dc2
=================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
--  Address        Load       Tokens  owns (effective)  Host ID                               Rack
UN  10.186.60.68   74.23 KiB  16      100.0%            a7307228-62bb-4354-9853-990cac9614ab  rack2
UN  10.186.60.65   83.17 KiB  16      100.0%            89683bf8-aff8-4fdc-9525-c14764cf2d4f  rack2
UN  10.186.60.53   88.36 KiB  16      100.0%            7c91c707-abac-44f2-811O-b18f03f03d13  rack2
DN  10.186.60.94   74.23 KiB  16      100.0%            c8fa86e4-ee9a-4c62-b00b-d15edc967b9f  rack2

可以看到,94节点已经宕掉,但是 dc2 数据中心的 owns 分布并未改变。

查看数据分布在哪个节点:

[cassandra@data01 ~]$ nodetool getendpoints dcdatabase test 5
10.186.60.67
10.186.60.94
10.186.60.7
10.186.60.53
10.186.60.65
10.186.60.118
10.186.60.61
10.186.60.68

可以看到,数据仍分布在94节点上;

把故障节点94移除集群:

[cassandra@data02 ~]$ nodetool removenode c8fa86e4-ee9a-4c62-b00b-d15edc967b9f

查看集群状态:

[cassandra@data01 ~]$ nodetool status
Datacenter: dc1
=================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
--  Address        Load       Tokens  owns (effective)  Host ID                               Rack
UN  10.186.60.67   96.55 KiB  16      100.0%            9d6d759b-c00c-488b-938d-3e1ef9b92b02  rack1
UN  10.186.60.7    88.29 KiB  16      100.0%            4702178e-9878-48dc-97e7-9211b7c9f2e7  rack1
UN  10.186.60.118  88.33 KiB  16      100.0%            c920c611-2e8b-472d-93a4-34f1abd5b207  rack1
UN  10.186.60.61   88.37 KiB  16      100.0%            af2e0c42-3a94-4647-9716-c484b690899i  rack1

Datacenter: dc2
=================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
--  Address        Load       Tokens  owns (effective)  Host ID                               Rack
UN  10.186.60.68   74.23 KiB  16      100.0%            a7307228-62bb-4354-9853-990cac9614ab  rack2
UN  10.186.60.65   83.17 KiB  16      100.0%            89683bf8-aff8-4fdc-9525-c14764cf2d4f  rack2
UN  10.186.60.53   88.36 KiB  16      100.0%            7c91c707-abac-44f2-811O-b18f03f03d13  rack2


[cassandra@data02 ~]$ nodetool getendpoints dcdatabase test 5
10.186.60.67
10.186.60.7
10.186.60.53
10.186.60.65
10.186.60.118
10.186.60.61
10.186.60.68

可以看到,数据不在94节点上了;

说明:对于 cassandra 停止服务或移出集群,仍是可以使用的,只是不能登入自己的 cassandra 数据库,但仍可以登录其他 cassandra 数据库。

3.2、实验2:

CREATE KEYSPACE "dcdatabase" WITH REPLICATION = {'class':'NetworkTopologyStrategy', 'dc1' : 3, 'dc2' : 3};

查看集群状态:

[cassandra@data01 ~]$ nodetool status
Datacenter: dc1
=================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
--  Address        Load       Tokens  owns (effective)  Host ID                               Rack
UN  10.186.60.67   96.55 KiB  16      73.2%             9d6d759b-c00c-488b-938d-3e1ef9b92b02  rack1
UN  10.186.60.7    89.39 KiB  16      74.7%             4702178e-9878-48dc-97e7-9211b7c9f2e7  rack1
UN  10.186.60.118  88.33 KiB  16      77.4%             c920c611-2e8b-472d-93a4-34f1abd5b207  rack1
UN  10.186.60.61   88.42 KiB  16      74.7%             af2e0c42-3a94-4647-9716-c484b690899i  rack1

Datacenter: dc2
=================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
--  Address        Load       Tokens  owns (effective)  Host ID                               Rack
UN  10.186.60.68   74.22 KiB  16      100.0%            a7307228-62bb-4354-9853-990cac9614ab  rack2
UN  10.186.60.65   84.14 KiB  16      100.0%            89683bf8-aff8-4fdc-9525-c14764cf2d4f  rack2
UN  10.186.60.53   88.30 KiB  16      100.0%            7c91c707-abac-44f2-811O-b18f03f03d13  rack2

可以看到集群中,每个数据中心的 owns 都是 300% ,符合三副本的设置;

测试并查看集群中出现故障节点后的数据分布情况:

94机器关闭服务,并移除集群:

[cassandra@data02 ~]$ nodetool removenode c8fa86e4-ee9a-4c62-b00b-d15edc967b9f

查看集群状态:

[cassandra@data01 ~]$ nodetool status
Datacenter: dc1
=================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
--  Address        Load       Tokens  owns (effective)  Host ID                               Rack
UN  10.186.60.67   96.55 KiB  16      73.2%             9d6d759b-c00c-488b-938d-3e1ef9b92b02  rack1
UN  10.186.60.7    89.39 KiB  16      74.7%             4702178e-9878-48dc-97e7-9211b7c9f2e7  rack1
UN  10.186.60.118  88.33 KiB  16      77.4%             c920c611-2e8b-472d-93a4-34f1abd5b207  rack1
UN  10.186.60.61   88.42 KiB  16      74.7%             af2e0c42-3a94-4647-9716-c484b690899i  rack1

Datacenter: dc2
=================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
--  Address        Load       Tokens  owns (effective)  Host ID                               Rack
UN  10.186.60.68   74.22 KiB  16      100.0%            a7307228-62bb-4354-9853-990cac9614ab  rack2
UN  10.186.60.65   84.14 KiB  16      100.0%            89683bf8-aff8-4fdc-9525-c14764cf2d4f  rack2
UN  10.186.60.53   88.30 KiB  16      100.0%            7c91c707-abac-44f2-811O-b18f03f03d13  rack2

此时,数据不在94节点上了,故障节点上的数据已移动到其他节点上,因此可以看到,在 dc1 数据中心中,数据随机仍只分布在其中三个节点上,而 dc2 数据中心的数据将分布在了仅有的三个节点上,发生了数据转移;

如果此时 dc2 数据中心还有节点继续故障,那么故障节点上的数据不可能再移动到其他节点上了,dc1 是不变的,owns 还是300% ,但是 dc2 的 owns都是100% ,没办法故障转移了,只能存在自身的数据了;

此时重启所有主机,所有主机 Cassandra 服务都会开启,包括之前故障模拟的节点也会自启,那么此时就会达到了另一种效果:故障模拟节点后的状态,再添加到了集群中,那么此时数据又会进行了自动的分发。

查看集群状态:

[cassandra@data01 ~]$ nodetool status
Datacenter: dc1
=================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
--  Address        Load       Tokens  owns (effective)  Host ID                               Rack
UN  10.186.60.67   96.55 KiB  16      73.2%             9d6d759b-c00c-488b-938d-3e1ef9b92b02  rack1
UN  10.186.60.7    89.39 KiB  16      74.7%             4702178e-9878-48dc-97e7-9211b7c9f2e7  rack1
UN  10.186.60.118  88.33 KiB  16      77.4%             c920c611-2e8b-472d-93a4-34f1abd5b207  rack1
UN  10.186.60.61   88.42 KiB  16      74.7%             af2e0c42-3a94-4647-9716-c484b690899i  rack1

Datacenter: dc2
=================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
--  Address        Load       Tokens  owns (effective)  Host ID                               Rack
UN  10.186.60.68   74.22 KiB  16      73.2%             a7307228-62bb-4354-9853-990cac9614ab  rack2
UN  10.186.60.65   84.14 KiB  16      74.7%             89683bf8-aff8-4fdc-9525-c14764cf2d4f  rack2
UN  10.186.60.53   88.30 KiB  16      74.7%             7c91c707-abac-44f2-811O-b18f03f03d13  rack2
UN  10.186.60.94   90.12 KiB  16      77.4%             c8fa86e4-ee9a-4c62-b00b-d15edc967b9f  rack2

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