As of Oracle Database 10g release 10.2, if Streams functionality is used, but the STREAMS_POOL_SIZE initialization parameter is not defined, then the size of the streams pool automatically defaults to 10% of size of the shared pool.
When the streams pool is created, the required SGA memory is taken from memory allocated to the buffer cache, reducing the size of the cache to less than what was specified by the DB_CACHE_SIZE initialization parameter. This means that if the buffer cache was configured with only the minimal required SGA, then Data Pump operations may not work properly.
需要流池，流池是用于缓存流进程用于移动和复制数据所使用的队列消息，expdp是oracle的内部提供的api