Increasing Db2 Connect data transfer rates

In addition to blocking of rows for a query result set, Db2® for z/OS® can also return multiple such query blocks in response to an OPEN or FETCH request to a remote client, such as Db2 Connect. Instead of the client repeatedly sending requests to the Db2 for z/OS server requesting one block of row data at a time, the client can now optionally request that the server send back some number of query blocks in addition to the one that it will always send back. Such additional query blocks are called extra query blocks.

As such, this new feature allows the client to minimize the number of network line turnarounds, which constitute a major cost to network performance. The decrease in the number of requests sent by the client to the server for query blocks translates into a significant performance boost. This performance boost is due to the fact that switching between a send and receive is an expensive operation performance-wise. Db2 Connect can now exploit this performance enhancement by requesting extra query blocks from a Db2 for z/OS server by default.

To fully take advantage of the return of extra query blocks (each of which can be up to 32K bytes long) for the preferred network protocol of TCP/IP, window scaling extensions have been enabled as architected under RFC-1323 in Db2 Connect. This feature that allows TCP/IP to dynamically adjust the send and receive window sizes to accommodate the potentially large amounts of data returned by way of the extra query blocks efficiently.