Abstract: A system is described for processing schema updated in a zero-downtime environment. A technique includes establishing an application session to access a database, receiving a schema update, converting the database to an updated database according to the schema update after establishing the application session, generating a temporary compensation view from the schema update, the temporary compensation view containing compensation logic to locate database objects belonging to the database, receiving a database transaction from the application session to access a database object in the database; and processing the compensation logic to locate the database object.

Abstract: A system is described for processing schema updated in a zero-downtime environment. A technique includes establishing an application session to access a database, receiving a schema update, converting the database to an updated database according to the schema update after establishing the application session, generating a temporary compensation view from the schema update, the temporary compensation view containing compensation logic to locate database objects belonging to the database, receiving a database transaction from the application session to access a database object in the database; and processing the compensation logic to locate the database object.

Abstract: A database system with improved query execution performance is described. In order to achieve as much accuracy as possible by optimizing large block I/O related query plans, the database system implements a methodology employing two new statistical measures for use in a database server. The first statistical measure, called “Data Page Cluster Ratio” (DPCR), indicates the “packing” of data pages by measuring the “clustering” property of the data pages, i.e., how well clustered the consecutive data pages of a given relational table are in the extents. The ratio is measured for data pages accesses either via a scan of an index or via a scan of the table. The second statistical measure, called Index Page Cluster Ratio (IPCR), indicates the “packing” of index leaf pages by measuring the “clustering” property of index pages, i.e., how well clustered the consecutive index leaf pages of a given relational table's index are in the extents.