Feature Idea : Support Read Replicas

首先检查 pg-pool 的 constructor、connect 和 query API，然后研究当前的客户端选择和连接管理方式。定义受支持的只读副本配置以及读写路由行为，包括调用方是否传入 isWrite，还是对查询进行解析；完成的标准是多集群连接池能够正常工作，同时不破坏现有的单集群用法。

node-postgres handles connection pooling seemlessly with a single cluster
Although it doesn't have support for multi cluster connection management
This will be useful in production deployments having multiple read replicas with a single master cluster used with write operations

Idea :
Allow a list of read clusters to be specified with pg-pool
with pg-pool handling connection management with multi-clusters automatically

Implementation Approach :
pg-pool has a constructor accepting a list of endpoints for read replicas , primary cluster ( used with write )

Internally A MultiClient Pool Manager will maintain the list of clients with public methods for picking a client for read or write
Client Pick Strategy For Read :
MultiClientPool will pick a cluster which has an idle connection if available , else it will resolve to creating a new connection by picking the one with min active connections

pg-pool has connect , query methods used by end clients , clients can have an option to specify an operation as read or write
Ex : through a parameter isWrite ,
pg-pool passes the parameter to MultiClientPool to pick a cluster

Alternative Approach to read-write detection

1. Implement a parser to auto identify a query as read or write

For Projects
It simplifies scaling read heavy workloads through usage of multi clusters