强读复制表路由

复制表是 OceanBase 数据库中的一种特殊表结构，支持在任意一个副本读取数据的最新修改，适合于对写入频率要求较低，读延时和读负载均衡要求较高的场景。复制表的详细信息可参见 OceanBase 数据库文档 创建表 一文。

示例

1. 执行如下命令创建复制表

   obclient [test]> CREATE TABLE TEST.DUP(C1 INT) DUPLICATE_SCOPE = 'cluster';
   

2. 为待执行的 SQL 语句提供分区键值，示例如下

   obclient [test]> SELECT * FROM TEST.DUP WHERE C1=123\G
   

3. 执行 EXPLAIN ROUTE 命令查看 ODP 路由选取过程

   obclient [test]> EXPLAIN ROUTE SELECT * FROM test.dup WHERE C1=123\G
   

   输出如下，ODP 根据 DUP_REPLICA_FIRST 路由策略进行路由。

   ...
   > ROUTE_POLICY
     [INFO] Strong read duplicated table. Ignore proxy route policy and session route policy
   
   Route Plan
   -----------------
   > SQL_PARSE:{cmd:"COM_QUERY", table:"dup"}
   > ROUTE_INFO:{route_info_type:"USE_PARTITION_LOCATION_LOOKUP"}
   > LOCATION_CACHE_LOOKUP:{mode:"oceanbase"}
     > TABLE_ENTRY_LOOKUP_START:{}
       > FETCH_TABLE_RELATED_DATA:{table_entry:"not partition table or part info no exists"}
     > TABLE_ENTRY_LOOKUP_DONE:{table:"dup", table_id:500685, table_type:"USER TABLE", has_dup_replica:true}
   > ROUTE_POLICY:{replica:"10.10.10.2:50110", idc_type:"SAME_IDC", zone_type:"ReadWrite", role:"FOLLOWER", type:"FULL", is_dup_replica:true, is_partition_server:true, chosen_route_type:"ROUTE_TYPE_DUP_PARTITION_UNMERGE_LOCAL", route_policy:"DUP_REPLICA_FIRST", trans_consistency:"STRONG", session_consistency:"STRONG", proxy_idc_name:"zue"}
   > CONGESTION_CONTROL:{svr_addr:"10.10.10.2:50110"}