3.3.3. Best Practices: Multi-Site/Active-Active Clusters

Note

The procedures in this section are designed for the Multi-Site/Active-Active topology ONLY. Do NOT use these procedures for Composite Active/Active Clustering uing v6 onwards.

For version 6.x onwards, Composite Active/Active Clustering, please refer to Section 3.4, “Deploying Composite Active/Active Clusters”

Note

In addition to this information, follow the guidelines in Section 2.5, “Best Practices”.

  • Running a Multi-Site/Active-Active service uses many different components to keep data updated on all servers. Monitoring the dataservice is divided into monitoring the two different clusters. Be mindful when using commands that you have the correct path. You should either use the full path to the command under /opt/continuent and /opt/replicator, or use the aliases created by setting the --executable-prefix=mm option. Calling trepctl would become mm_trepctl.

  • Configure your database servers with distinct auto_increment_increment and auto_increment_offset settings. Each location that may accept writes should have a unique offset value.

Using cctrl gives you the dataservice status individually for the east and west dataservice. For example, the east dataservice is shown below:

Continuent Tungsten 6.0.5 build 40
east: session established
[LOGICAL] /east > ls

COORDINATOR[east1:AUTOMATIC:ONLINE]

ROUTERS:
+----------------------------------------------------------------------------+
|connector@east1[17951](ONLINE, created=0, active=0)                         |
|connector@east2[17939](ONLINE, created=0, active=0)                         |
|connector@east3[17961](ONLINE, created=0, active=0)                         |
+----------------------------------------------------------------------------+

DATASOURCES:
+----------------------------------------------------------------------------+
|east1(master:ONLINE, progress=29, THL latency=0.739)                        |
|STATUS [OK] [2013/11/25 11:24:35 AM GMT]                                    |
+----------------------------------------------------------------------------+
|  MANAGER(state=ONLINE)                                                     |
|  REPLICATOR(role=master, state=ONLINE)                                     |
|  DATASERVER(state=ONLINE)                                                  |
|  CONNECTIONS(created=0, active=0)                                          |
+----------------------------------------------------------------------------+

+----------------------------------------------------------------------------+
|east2(slave:ONLINE, progress=29, latency=0.721)                             |
|STATUS [OK] [2013/11/25 11:24:39 AM GMT]                                    |
+----------------------------------------------------------------------------+
|  MANAGER(state=ONLINE)                                                     |
|  REPLICATOR(role=slave, master=east1, state=ONLINE)                        |
|  DATASERVER(state=ONLINE)                                                  |
|  CONNECTIONS(created=0, active=0)                                          |
+----------------------------------------------------------------------------+

+----------------------------------------------------------------------------+
|east3(slave:ONLINE, progress=29, latency=1.143)                             |
|STATUS [OK] [2013/11/25 11:24:38 AM GMT]                                    |
+----------------------------------------------------------------------------+
|  MANAGER(state=ONLINE)                                                     |
|  REPLICATOR(role=slave, master=east1, state=ONLINE)                        |
|  DATASERVER(state=ONLINE)                                                  |
|  CONNECTIONS(created=0, active=0)                                          |
+----------------------------------------------------------------------------+

When checking the current status, it is import to compare the sequence numbers from each service correctly. There are four services to monitor, the Tungsten Cluster service east, and a Tungsten Replicator service east that reads data from the west Tungsten Cluster service. A corresponding west Tungsten Cluster and west Tungsten Replicator service.

  • When data is inserted on the Primary within the east Tungsten Cluster, use cctrl to determine the cluster status. Sequence numbers within the Tungsten Cluster east should match, and latency between hosts in the Tungsten Cluster service are relative to each other.

  • When data is inserted on east, the sequence number of the east Tungsten Cluster service and east Tungsten Replicator service (on west{1,2,3}) should be compared.

  • When data is inserted on the Primary within the east Tungsten Cluster, use cctrl to determine the cluster status. Sequence numbers within the Tungsten Cluster east should match, and latency between hosts in the Tungsten Cluster service are relative to each other.

  • When data is inserted on west, the sequence number of the west Tungsten Cluster service and west Tungsten Replicator service (on east{1,2,3}) should be compared.

  Tungsten Cluster Service Seqno Tungsten Replicator Service Seqno
Operation east west east west
Insert/update data on east Seqno Increment   Seqno Increment  
Insert/update data on west   Seqno Increment   Seqno Increment

Within each cluster, cctrl can be used to monitor the current status. For more information on checking the status and controlling operations, see Section 5.3, “Checking Dataservice Status”.

Note

For convenience, the shell PATH can be updated with the tools and configuration. With two separate services, both environments must be updated. To update the shell with the Tungsten Cluster service and tools:

shell> source /opt/continuent/share/env.sh

To update the shell with the Tungsten Replicator service and tools:

shell> source /opt/replicator/share/env.sh

To monitor all services and the current status, you can also use the multi_trepctl command (part of the Tungsten Replicator installation). This generates a unified status report for all the hosts and services configured:

shell> multi_trepctl --by-service
| host  | servicename | role   | state  | appliedlastseqno | appliedlatency |
| east1 | east        | master | ONLINE |               53 |        120.161 |
| east3 | east        | master | ONLINE |               44 |          0.697 |
| east2 | east        | slave  | ONLINE |               53 |        119.961 |
| west1 | east        | slave  | ONLINE |               53 |        119.834 |
| west2 | east        | slave  | ONLINE |               53 |        181.128 |
| west3 | east        | slave  | ONLINE |               53 |        204.790 |
| west1 | west        | master | ONLINE |           294327 |          0.285 |
| west2 | west        | master | ONLINE |           231595 |          0.316 |
| east1 | west        | slave  | ONLINE |           294327 |          0.879 |
| east2 | west        | slave  | ONLINE |           294327 |          0.567 |
| east3 | west        | slave  | ONLINE |           294327 |          1.046 |
| west3 | west        | slave  | ONLINE |           231595 |         22.895 |

In the above example, it can be seen that the west services have a much higher applied last sequence number than the east services, this is because all the writes have been applied within the west cluster.

To monitor individual servers and/or services, use trepctl, using the correct port number and servicename. For example, on east1 to check the status of the replicator within the Tungsten Cluster service:

shell> trepctl status

To check the Tungsten Replicator service, explicitly specify the port and service:

shell> mm_trepctl -service west status