ApsaraDB for Redis is a database service compatible with the open source Redis protocol and provides hybrid storage of memory and disks. Based on reliable hot standby architectures and scalable cluster architectures, ApsaraDB for Redis is suitable for scenarios that require flexible configuration changes, high throughput, and low latency. This topic describes how to synchronize data from a Codis cluster to an ApsaraDB for Redis instance by using Data Transmission Service (DTS).
- An ApsaraDB for Redis instance is created as the destination instance, and the database version of the instance is 2.8, 4.0, or 5.0. For more information, see Step 1: Create an ApsaraDB for Redis instance.
- The available storage capacity of the destination ApsaraDB for Redis instance is larger than the total size of data stored in the source Codis cluster.
- All master nodes in the source Codis cluster support the
How DTS synchronizes data from a Codis cluster
A Codis cluster consists of multiple codis-groups. You must create a data synchronization task for each codis-group. DTS synchronizes each codis-group in a data synchronization task until the whole cluster is synchronized.
Architecture of the Codis cluster
In this topic, a Codis cluster that consists of two codis-groups is used. Each codis-group runs in a master-replica architecture. The following figure shows the architecture of the cluster.
- DTS uses the resources of the source and destination databases during full data synchronization. This may increase the loads of the database servers. If you migrate a large volume of data or if the server specifications cannot meet your requirements, database services may become unavailable. Before you synchronize data, evaluate the impact of data synchronization on the performance of the source and destination instances. We recommend that you synchronize data during off-peak hours.
- If the
bindparameter is configured in the redis.conf file of the source database, you must set the value of this parameter to the internal IP address of the ECS instance. The setting ensures that DTS can connect to the source database.
- To ensure the stability of data synchronization, we recommend that you increase the
value of the repl-backlog-size parameter in the
redis.conffile of the source Codis cluster.
- To ensure the synchronization quality, DTS adds the following key to the source Codis
DTS_REDIS_TIMESTAMP_HEARTBEAT. This key is used to record the time when data is synchronized to the destination instance.
- We recommend that you do not run the
FLUSHALLcommand in the source Codis cluster. Otherwise, data may become inconsistent between the source and destination databases.
- If the data eviction policy (
maxmemory-policy) of the destination instance is not set to
noeviction, data may become inconsistent between the source and destination instances. For more information about data eviction policies, see How does ApsaraDB for Redis evict data by default?
- If an expiration policy is enabled for some keys in the source database, these keys
may not be deleted in a timely manner after they expired. Therefore, the number of
keys in the destination database may be less than that in the source database. You
can run the info command to view the number of keys in the destination database.
Note The number of keys that do not have an expiration policy or have not expired is the same in the source and destination databases.
- The database version of the destination ApsaraDB for Redis instance must be 2.8, 4.0, or 5.0. The version of the destination database must be the same as or later than the version of the source database. If you synchronize data between different versions of Redis databases, make sure that the versions of the source and destination databases are compatible with each other. For example, you can create a destination pay-as-you-go ApsaraDB for Redis instance to verify the compatibility between the source and destination databases. Then, you can release the instance or change the billing method of the instance to subscription.
Supported synchronization topology
- One-way one-to-one synchronization
- One-way one-to-many synchronization
- One-way cascade synchronization
For more information, see Synchronization topologies.
Commands that can be synchronized
- BITOP, BLPOP, BRPOP, and BRPOPLPUSH
- DECR, DECRBY, and DEL
- EVAL, EVALSHA, EXEC, EXPIRE, and EXPIREAT
- GEOADD and GETSET
- HDEL, HINCRBY, HINCRBYFLOAT, HMSET, HSET, and HSETNX
- INCR, INCRBY, and INCRBYFLOAT
- LINSERT, LPOP, LPUSH, LPUSHX, LREM, LSET, and LTRIM
- MOVE, MSET, MSETNX, and MULTI
- PERSIST, PEXPIRE, PEXPIREAT, PFADD, PFMERGE, PSETEX, and PUBLISH
- RENAME, RENAMENX, RESTORE, RPOP, RPOPLPUSH, RPUSH, and RPUSHX
- SADD, SDIFFSTORE, SELECT, SET, SETBIT, SETEX, SETNX, SETRANGE, SINTERSTORE, SMOVE, SPOP, SREM, and SUNIONSTORE
- ZADD, ZINCRBY, ZINTERSTORE, ZREM, ZREMRANGEBYLEX, ZUNIONSTORE, ZREMRANGEBYRANK, and ZREMRANGEBYSCORE
- PUBLISH commands cannot be synchronized.
- If you run the EVAL or EVALSHA command to call Lua scripts, DTS cannot identify whether these Lua scripts are executed on the destination instance. This is because the destination instance does not explicitly return the execution results of Lua scripts during incremental data synchronization.
- When DTS runs the SYNC or PSYNC command to transfer data of the LIST type, DTS does not clear the existing data. As a result, the destination instance may contain duplicate data records.
- Purchase a data synchronization instance. For more information, see Purchase a DTS instance. Note On the buy page, set Source Instance to Redis, set Destination Instance to Redis, and set Synchronization Topology to One-Way Synchronization.
- Log on to the DTS console.
- In the left-side navigation pane, click Data Synchronization.
- At the top of the Synchronization Tasks page, select the region where the destination instance resides.
- Find the data synchronization instance and click Configure Synchronization Channel in the Actions column.
- Configure the source and destination instances.
Section Parameter Description None Synchronization Task Name DTS generates a task name. We recommend that you specify an informative name to identify the task. You do not need to use a unique task name. Source Instance Details Instance Type Select User-Created Database in ECS Instance. Instance Region The source region that you selected on the buy page. The value of this parameter cannot be changed. ECS Instance ID Select the ID of the Elastic Compute Service (ECS) instance that hosts the master node of the codis-group.Note DTS synchronizes each codis-group of the Codis cluster by using a data synchronization task until the entire cluster is synchronized. In this step, enter the ECS instance ID of the master node for codis-group 1. When you configure the data synchronization task for codis-group 2, enter the ECS instance ID of the master node for codis-group 2. You can configure data synchronization tasks for all codis-groups by following the procedure described in this topic. Database Type The value of this parameter is set to Redis. Instance Mode Select Standalone.Note You must select Standalone for this parameter because data from a Codis cluster cannot be synchronized at a time. DTS synchronizes each codis-group of the cluster in a data synchronization task until all codis-groups are synchronized. Port Number Enter the service port number of the master node in the codis-group. Database Password The database password of the master node.Note This parameter is optional and can be left blank if no database password is set. Destination Instance Details Instance Type Select Redis Instance. Instance Region The region of the destination cluster. The region is the same as the destination region that you selected on the buy page. The value of this parameter cannot be changed. Instance ID Select the ID of the destination ApsaraDB for Redis instance. Database Password Enter the database password of the ApsaraDB for Redis instance.Note The database password is in the <user>:<password> format. For example, if the username of a custom account is admin and the password is Rp829dlwa, the database password is admin:Rp829dlwa.
- Select the processing mode of conflicting tables and the objects to be synchronized.
Parameter Description Select the processing mode of conflicting tables DTS synchronizes each codis-group of the Codis cluster in a data synchronization task until the whole cluster is synchronized. When you configure data synchronization for codis-group 1, select Pre-check and Intercept if the ApsaraDB for Redis instance has no data. When you configure data synchronization for codis-groups 2 to N, select Ignore. Otherwise, errors may occur during data synchronization.Note
- Pre-check and Intercept: checks whether the destination database is empty. If the destination database is empty, the precheck is passed. If the database is not empty, an error is returned during the precheck and the data synchronization task cannot be started.
- Ignore: skips the precheck for empty destination databases and continues with data synchronization. If the keys in the destination database are the same as those in the source database during data synchronization, the keys in the source database overwrite those in the destination database.
Select the objects to be synchronized
- Select one or more databases from the Available section and click to move the databases to the Selected section.
- You can select only databases as the objects to be synchronized. You cannot select keys as the objects to be synchronized.
Rename Databases and Tables In this scenario, you cannot rename objects. Replicate Temporary Tables When DMS Performs DDL OperationsIf you use Data Management (DMS) to perform online DDL operations on the source database, you can specify whether to synchronize temporary tables generated by online DDL operations.
- Yes: DTS synchronizes the data of temporary tables generated by online DDL operations.
Note If online DDL operations generate a large amount of data, the data synchronization task may be delayed.
- No: DTS does not synchronize the data of temporary tables generated by online DDL operations.
Only the original DDL data of the source database is synchronized.
Note If you select No, the tables in the destination database may be locked.
Retry Time for Failed ConnectionsBy default, if DTS fails to connect to the source or destination database, DTS retries within the next 720 minutes (12 hours). You can specify the retry time based on your needs. If DTS reconnects to the source and destination databases within the specified time, DTS resumes the data synchronization task. Otherwise, the data synchronization task fails.Note When DTS retries a connection, you are charged for the DTS instance. We recommend that you specify the retry time based on your business needs. You can also release the DTS instance at your earliest opportunity after the source and destination instances are released.
- In the lower-right corner of the page, click Next.
- Configure initial synchronization. Note The value is set to Include full data + incremental data. DTS synchronizes historical data from the source Codis cluster to the destination Redis databases and then synchronizes incremental data.
- In the lower-right corner of the page, click Precheck. Note
- Before you can start the data synchronization task, DTS performs a precheck. You can start the data synchronization task only after the task passes the precheck.
- If the task fails to pass the precheck, you can click the icon next to each failed item to view details.
- You can troubleshoot the issues based on the causes and run a precheck again.
- If you do not need to troubleshoot the issues, you can ignore failed items and run a precheck again.
- Close the Precheck dialog box after the following message is displayed: The precheck is passed. Then, the data synchronization task starts.
- Wait until initial synchronization is completed and the data synchronization task
enters the Synchronizing state. Note You can view the state of the data synchronization task on the Synchronization Tasks page.
- Create and configure a data synchronization task for the other codis-group by repeating Steps 1 to 13.
In this topic, the Codis cluster consists of two codis-groups. You must create two data synchronization tasks. The following figure shows that the initial synchronization is complete for both tasks and both tasks are in the Synchronizing state.
In this topic, databases DB0 and DB1 are synchronized. You can use Data Management (DMS) to log on to the ApsaraDB for Redis instance and check the total number of keys in the ApsaraDB for Redis instance. The total number of keys is the same as that in the source Codis cluster. For more information about how to use DMS to log on to an ApsaraDB for Redis instance, see Use DMS to log on to an ApsaraDB for Redis instance.