我对连接池有点困惑。我在 MySQL 数据库之上使用 Hibernate。Hibernate 的连接池策略由 c3p0 决定。
Hibernate 的连接池大小与 MySQL 之间的关系是什么？
我运行 Hibernate 的代码可以扩展到 AWS 上的多个实例（因此 n 个实例，每个实例的 Hibernate 连接池大小为 m）。然而，所有实例都与单个 RDS MySQL 实例通信，该实例本身具有连接池大小 q。
这是否意味着如果有 n*m 个活动连接并且 n*m>q，将有连接必须在 MySQL 的队列中等待？
谢谢！
Your question asks about "Hibernate's connection pool size vs MySQL's". The important distinction to keep in mind is:
A connection pool is an application concept, not a database one. The connection pool used by your application (i.e., Hibernate) is simply a way of speeding up the communication to the database. Since establishing each connection is relatively slow, it's more efficient to pre-establish a bunch of connections and then let your application use them as needed.
On the other hand, a database doesn't pool connections. Instead, it allows clients to establish connections upon request up to a max limit (e.g., the max_connections parameter in MySQL). If a client asks for a connection and the database has already hit the max limit, then a connection error will occur.
So to answer your question, if you configure your application connection pools to try to pre-establish more connections than the database will allow, you will get a "Too many connections" error from MySQL. This could be avoided by either raising the MySQL configuration parameter or by adjusting your c3p0 max pool size per instance.