最近的一个项目中，由于界面查询的数据量比较大，关联的表比较多，有些数据查出来需要临时保存起来供后面的查询使用，于是想到了用oracle的临时表来实现这个需求。大家都知道，oracle的临时表有两种：事务级别临时表和会话级别临时表，我这里使用的是会话级别的临时表。当时把功能时候后就以为万事大吉了，没想到就在这里买下了一个坑。
坑的浮现：之后在为系统加调试日志时偶然发现了临时表的数据没有像oracle临时表的定义那样“不同会话独享临时表，临时表的数据在会话结束后被自动清空”。首先看第一次查询的日志记录截图，第一次的查询数据量是10017行，红色框圈住的地方使用到临时表：
第二次查询的日志记录截图，第二次查询的数据量比第一次少，15行：
从这前后两次的查询结果来看，得到的结论是：使用到的oracle会话级别临时表没有像它定义那样，在会话结束后没有把临时表的数据清空？不过很明显不是因为这个原因了，最有可能的就是原因应该是，前后两次查询都是同一个Session，所以才导致临时表的数据没有被清空了。有了这个思路，接下来就是找到为什么前后两次的查询会是同一个Session。
追究坑出现的原因：
首先，系统环境：
1、使用的ADO.NET是默认启用了连接池，连接池配置使用默认的配置；
2、连接oracle数据库的驱动是：
3、每次查询都是新建一个Connection，然后都是在查询完后调用Close()、Dispose()；
查找坑出现的思路：
1、启用连接池后，前后两次查询使用的连接都是同一个连接；
2、查询完毕后，Connection调用Close()、Dispose()方法后并没有真正关闭Session；
验证过程：
首先看看oracle官方文档对Connection Pool的解释：
With connection pooling enabled (the default), the Open and Close methods of the OracleConnection object implicitly use the connection pooling service. In the preceding code, the Open call uses the connection pooling service, which is responsible for returning a connection to the application.
Connection pools are created by the connection pooling service using the ConnectionString as a signature to uniquely identify a pool.
If no pool with the exact attribute values in the ConnectionString exists, the connection pooling service creates a new connection pool. If a pool already exists with the requested signature, a connection is returned to the application from that
pool.
When a connection pool is created, the connection-pooling service initially creates the number of connections defined by the Min Pool Size attribute of the ConnectionString. This number of connections is always maintained by the connection pooling service for the connection pool.
At any given time, these connections are available in the pool or used by the application.
The Incr Pool Size attribute of the ConnectionString defines the number of new connections to be created by the connection pooling service when more connections are needed in the connection pool.
When the application closes a connection, the connection pooling service determines whether the connection lifetime has exceeded the Connection Lifetime attribute; if so, the connection pooling service closes the connection; otherwise, the connection goes back to the connection pool. The connection pooling service only enforces the Connection Lifetime when a connection is going back
to the connection pool.
The Max Pool Size attribute of the ConnectionString sets the maximum number of connections for a connection pool. If a new connection is requested, no connections are available, and Max Pool Size has been reached, then the connection pooling service waits for the time defined by Connection Timeout. If the Connection Timeout has been reached and there are still no connections
available in the pool, the connection pooling service raises an exception indicating that the pooled connection request has timed-out.
The connection pooling service closes connections when they are not used; connections are closed every three minutes. The Decr Pool Size attribute of the ConnectionString provides connection pooling service for the maximum number of connections that can be closed in one run.
Connection调用Open()方法时，以下是oracle官方文档描述：
The connection is obtained from the pool if connection pooling is enabled. Otherwise, a new connection is established.
It is possible that the pool does not contain any unused connections when the Open() method is invoked. In this case, a new connection is established.
Connection调用Close()方法时，以下是oracle官方文档描述：
Rolls back any pending transactions.
Places the connection to the connection pool if connection pooling is enabled. Even if connection pooling is enabled, the connection can be closed if it exceeds the connection lifetime specified in the connection string. If connection pooling is disabled, the connection is closed.
Closes the connection to the database.
The connection can be reopened using Open().
从oracle官方文档对于Connection Pool和Connection的Open、Close方法的描述和结合当前系统环境（查询请求只有一个客户端）来看，我们不难可以得到这么一个场景：第一次查询的时候，Connection Pool创建了一个连接返回给Connection对象，查询完后返回给连接池；在第二次查询时，由于跟第一次查询时间间隔小于默认的Connection LifeTime，Connection Pool就返回了第一次查询所用的连接给Connection对象用于查询，结果第一次和第二次用的连接都是同一个。再有，由Close()方法的描述来看，Connection调用Close方法时，并没有把连接的Session信息等数据清除掉（只有在连接真正从连接池移除掉之后，Session才没有）。
目前想到的解决办法有两个（最终决定使用第一个）：
1、在每次使用临时表之前先truncate一下临时表；
2、不使用Connection Pool；
第一次发文，主要是今天看了博主农码一生的博文《我们为什么应该坚持写博客》，然后顺便记录一下这个坑，请教园中各位前辈，有没有其他解决方法，或者是说，我解决问题的方向错了。请多多指教~~~