Abstract: An inexact query transformation system selects a query element from a query statement. If an inexact transformation improves the query performance, the system prioritizes the candidate transformation rules applicable to the selected query element. The system applies the candidate transformation rules to the selected query element to generate a transformed query element that includes a transformed remote query element. If the transformed remote query element is pushdownable, the system adds the transformed remote query element to a transformed inexact query output. Otherwise, the system applies additional candidate transformation rules to the selected query element to generate the transformed inexact query output. The system applies the transformed inexact query output to a heterogeneous datastore to provide an output query result.

Abstract: A method, apparatus and article of manufacture, implementing the method, of determines a target data type in an environment having a plurality of levels. Zero or more intermediate levels are between the source level and the target level. A target data type representing the transformation of a data type of an associated datum as the datum passes from the source level through the zero or more intermediate levels to the target level is generated. In another aspect of the invention, the datum is assigned to the target level in accordance with the target data type. In yet another aspect of the invention, the target data type is passed with the associated datum, via the zero or more intermediate levels to the target level.

Abstract: An efficient procedure for determining the set of buffer pool database pages that must be externalized to stable storage and for scheduling their write I/O's before release of a committing transaction's locks. In a multisystem database management system (DBMS) with high-speed shared external storage (SES) environment, a DBMS instance may follow "force-at-commit" protocol for a database that has intersystem read/write interest or may alternatively follow a "no-force-at-commit" policy when operating with a database for which only one system has interest. By introducing the concept of a series of unique ordinal numbers (ORD#) for each database assigned to buffer pool data pages whenever the page state changes from clean to dirty within a single DBMS instance, this procedure maintains a transaction page list (TPL) for each transaction in ORD# order.

Abstract: A method for ensuring data coherence while detecting whether the locally cached copy of a data page is invalid and responsively refreshing the locally cached page from a Shared Electronic Store (SES) in a multisystem shared disk environment. Locally cached data pages may become invalid in a multisystem shared disk environment because of transactions executed by other systems for the common database. Thus, whenever a transaction in a database management system (DBMS) instance desires to read or update a record in a locally cached data page, the DBMS must first verify validity for the locally cached copy and, for stale or invalid copies, must re-read and re-register the latest version in the SES. This invention provides a procedure for the necessary verification and refreshing steps that relies on page latching to serialize the combination of local multiuser and global multisystem activities. The procedure of this invention supports both record and page locking granularities.