Access Your iSeries Data Quickly and Simply

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Access Your iSeries Data Quickly and Simply

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Two query optimizers are in i5/OS (OS/400), CQE and SQE since V5R2 (see page 24-31 of this document: http://www-03.ibm.com/servers/enable...ion/ibp/dada/). CQE should be avoided as its flexibility in resolving queries is limited compared to SQE. Additionally, IBM's development efforts are focused solely on SQE. Within the same referenced pages Query/400, OPNQRYF and QQQQry API data access will for the known future be processed by CQE only. Logical files can cause performance issues as stated in the above pages and in a recent article by Dan Cruikshank that "specifying a DDS-defined logical file object on the FROM clause of an SQL statement forces CQE optimization. In addition, if a derived index (e.g., select/omit logical files) exists over any physical file object accessed during SQE optimization, the optimization will be rerouted to the CQE optimizer." (the article is here: http://www.systeminetwork.com/artarc...geView=Search). The difference in query run times between CQE and SQE have been as drastic as a query running for hours under CQE then running in seconds under SQE. Modifying queries and the database infrastructure to use SQE is a well placed investment with short-term and strategic benefits.