The C++ client library uses this value to limit the growth of the connection pool. Once an operation (a RPC or a download) completes the connection used for that operation is returned to the pool. If the pool is full one or more connections are released. Otherwise, the connection is cached for use in following RPCs or downloads.
The library does not create connections proactively, setting a high value may result in very few connections if your application does not need them. The library may create more connections than this option configures, for example if your application requests many simultaneous downloads. When the pool is full, the library typically releases older connections first, and tries to reuse newer connections if they are available. The library may release more than one connection when the pool becomes full.
