International Business Machines Corporation

Douglas James Doole

Ian R Finlay

Timothy Jon Vincent

Sean W McKeough

George M Wilson

Paul Miller Bird

Paul C Huffman

John E Lumby

Melissa N Bousfield

A pre-pass and direct call mechanism which replaces the interpreter. The mechanism moves static decisions out of the repeated runtime path, into a pre-pass operation. Advantageously, the mechanism reduces runtime overhead, and improves overall performance of the DBMS during runtime, while maintaining the considerable investment in opcode generation and plan representation, already invested in the implementation of the DBMS.

Direct call threaded code

A pre-pass and direct call mechanism which replaces the interpreter. The mechanism moves static decisions out of the repeated runtime path into a pre-pass operation. Advantageously, the mechanism reduces runtime overhead and improves overall performance of the DBMS during runtime, while maintaining the considerable investment in opcode generation and plan representation.

Conflict checking for writing operations in an SQL database system is carried out for nested statements invoked by a parent statement. Each statement has an associated table access data structure defined at compile-time indicating the tables in the database that the statement accesses and the mode of access. At execution-time the table access data structure for each nested statement is accessed and the information is compared with a list of tables maintained for the parent statement to determine if there is a read/write or write/write conflict possible if the nested statement is executed. Where there is no conflict detected, the information from the table access data structure is copied to the list of tables.

Detection and prevention of writing conflicts within nested query statements

Library management for libraries of user-defined routines in a database system. Libraries are stored in a long-term storage device and loaded into working memory in the database system when routines in the libraries are to be executed. An unload thread is defined to carry out the process of unloading libraries from the working memory when such libraries are inactive. The unload thread becomes active on a defined timing interval. The unload thread accesses a hash table and a most recently used list to determine which of the loaded libraries is inactive and which of the libraries ought to be unloaded. The hash table maintains information as to which libraries have been accessed in the most recent past defined timing interval. The size of the most recently used list can be defined such that all libraries associated with the list are retained in working memory.

Management of user-defined routine libraries in database environments

A database management system provides for the execution of invokable user-defined routines. Applications specify user-defined routines as being threadsafe or not threadsafe and specify the language of user-defined routines. Execution of routines will be carried out dependent on the threadsafe characteristic of the routines and on the language of the routines. Routines are assigned to processes based on their language to have any given process execute routines of the same language. Routines that are specified to be threadsafe are executed in threads in a potentially multi-threaded process. Each routine that is specified to be not threadsafe is executed in a fenced-mode processes in which no other routine is being executed.

Mechanism for invocation of user-defined routines in a multi-threaded database environment

The invention provides a method and apparatus including a programming product for a parallel data processing system having a plurality of nodes interconnected by communication paths, in which one or more sets of data present at one or more source nodes of the system is required to be sent on a plurality of communication paths having communication buffers to selected nodes of the database system for processing, a system of communicating the data over the paths between the nodes to avoid deadlocking the processing system, including: accessing data from the one or more source nodes in subsets of the data; sending the subsets of data on a plurality of paths to the selected nodes of the processing system; if a path of the paths intended for the sending of one or more of the subsets of data becomes blocked, suspending the sending of subsets of the data on the path for a predetermined time period; if the blocked path becomes capable of accepting additional data before the predetermined time period has expired, resuming the sending of subsets of data on the path; however, if the predetermined time period expires without the path becoming available, placing one or more subsequent subsets of data intended for the path into an overflow buffer; when the blocked path again becomes free, sending the subsets of data from the overflow buffer on the path to the intended recipient node for processing.

System for internode deadlock avoidance in parallel database system using as overflow buffer a temporary table storage allocated to the parallel database application program being executed

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Don Mills, Canada

Douglas James Doole