guluo2016 commented on code in PR #8459: URL: https://github.com/apache/hbase/pull/8459#discussion_r3550941712
########## hbase-website/app/pages/_docs/docs/_mdx/(multi-page)/read-replica-cluster.mdx: ########## @@ -0,0 +1,201 @@ +--- +title: "Read Replica Cluster" +description: "Running a secondary HBase cluster in read-only mode against shared cloud storage to scale read workloads." +--- + +## Background [#read-replica-cluster-background] + +A _Read Replica Cluster_ is an entire HBase cluster running in global read-only mode against the same shared +storage (`hbase.rootdir`) as an active read-write cluster. Both clusters list the same HFiles in the same +HDFS / cloud-object-store location; no data is copied. Reads can be served from either cluster, letting the +read workload be fanned out across multiple clusters without doubling storage cost. + +Typical use cases: + +- Fan out heavy scan / analytical workloads off the primary cluster. +- Add cross-availability-zone read capacity backed by a single shared bucket. +- Stand up an isolated cluster for read-mostly experiments without copying data. + +<Callout type="info"> + **Eventual consistency.** A replica only sees data once (a) the active cluster has flushed the data to + HFiles in shared storage, and (b) the replica has been told to re-read shared storage via the + `refresh_meta` and `refresh_hfiles` commands. MemStore data on the active cluster is invisible to the + replica until flushed. +</Callout> + +The parent design lives on [HBASE-29081](https://issues.apache.org/jira/browse/HBASE-29081). + +## Design + +The feature has three parts. + +### Custom `hbase:meta` per cluster + +Every cluster sharing a `hbase.rootdir` needs its own `hbase:meta`, because region assignments are +node-scoped and cannot be shared. Other system tables (`hbase:namespace`, `hbase:acl`, `hbase:replication`) Review Comment: `hbase:namespace` has been deprecated since 3.0.0 and will be removed in 4.0.0. https://github.com/apache/hbase/blob/master/hbase-common/src/main/java/org/apache/hadoop/hbase/TableName.java#L110-L118 We don't need to mention it here for master branch. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
