One of the most time-consuming procedures of a database application is establishing a connection. The connection pooling of the data source can be used to minimize this overhead. That argues for using the data source instead of accessing the database driver directly.
Configuring the size of the pool in the data source is somewhere between an art and science - this article will try to move it closer to science.
From the beginning, WLS data source has had an initial capacity and a maximum capacity configuration values. When the system starts up and when it shrinks, initial capacity is used. The pool can grow to maximum capacity. Customers found that they might want to set the initial capacity to 0 (more on that later) but didn’t want the pool to shrink to 0. In WLS 10.3.6, we added minimum capacity to specify the lower limit to which a pool will shrink. If minimum capacity is not set, it defaults to the initial capacity for upward compatibility. We also did some work on the shrinking in release 10.3.4 to reduce thrashing; the algorithm that used to shrink to the maximum of the currently used connections or the initial capacity (basically the unused connections were all released) was changed to shrink by half of the unused connections.
The simple approach to sizing the pool is to set the initial/minimum capacity to the maximum capacity. Doing this creates all connections at startup, avoiding creating connections on demand and the pool is stable. However, there are a number of reasons not to take this simple approach. Read the full article here.
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