International Business Machines Corporation

John E Lumby

Calisto Paul Zuzarte

Peter Haas

Walid Rjaibi

John Frederick Hornibrook

Douglas James Doole

Paul C Huffman

The estimate of the selectivity of a HAVING clause in an SQL query is carried out within a specified time constraint by determining a selectivity estimate for each member in a sample set of group sizes for the HAVING clause using a probabilistic model based on an assumed value distribution. The selectivity estimates for the groups in the sample set are used to interpolate estimates for all possible group sizes and the estimates are combined based on an assumed known group size distribution to provide an estimation of the selectivity for the HAVING clause. Different selectivity estimating approaches are used for each group size based on available time for estimating and on the estimated time to complete the estimate using different techniques.

Selectivity estimation for processing SQL queries containing having clauses

A system and process for evaluating the performance of an operational database system without interfering with the normal operation of the operational database system is described. The process involves the creation of a test database which contains the system catalogs of the operational database system as user tables. The test database is used to compile queries using these simulated system catalogs. The access plan generated by the compilation in the test database can then be used to evaluate the performance of the queries.

System and process for evaluating the performance of a database system

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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Toronto, Canada

John E Lumby