Open connections as needed instead of all at once

[phette]

The initial call to acquire a connection opens all connections up to the max size. For anyone requiring a larger connection pool this becomes a relatively slow operation. Depending on the efficiency of your application you may not need to have the max number of connections open anyways. For those reasons I believe connections should be opened as needed until the max number of connections are reached.

https://github.com/aio-libs/aiomcache/blob/master/aiomcache/pool.py#L40-L44

[asvetlov]

It is a tradeoff between startup time and operation response one.
Please take a note that the client has two parameters: minimal and maximum size.
Setting the minimum size to non-zero value is very useful: it raises an exception if memcache server is not available on application startup (misconfiguration error most likely).
It's better than a random failure on request processing.