SYSTEM AND PROGRAM FOR IMPLEMENTING SCROLLABLE CURSORS IN A DISTRIBUTED DATABASE SYSTEM

• US 20090112886A1
• Filed: 01/05/2009
• Published: 04/30/2009
• Est. Priority Date: 03/28/2001
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Cotner, Curt Lee, Dong, Margaret A.
• Granted Patent: US 7,991,796 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G06F 16/284 Relational databases
• CPC Class Codes: Y10S 707/99931 Database or file accessing

Abstract

Provided are a system and program for accessing data in a distributed database environment. A client program receives multiple requests for data from a database object satisfying specified search predicates from an application program. Each request includes a request for at least one row from the table. The client program transfers a database command and a rowset parameter indicating a maximum number of rows to return to a server program over a network if the requested row is not maintained by the client program. A data block is generated with the server program including rows from the database object satisfying the search predicates in response to the database command. The rows included in the data block do not exceed the rowset parameter. The server program transfers the data block to the client program. In turn, the client program returns at least one requested row from the received data block in response to one request for the at least one row of data from the application program.

Claims

1. A system for accessing data in a distributed database environment, wherein the system is in communication with a server program over a network, wherein the system is in communication with an application program, and wherein the distributed database environment includes a database object, the system comprising:

a client computer; and

a client program executed by the client computer to perform;

(i) receiving multiple requests for data from the database object satisfying specified search predicates from the application program, wherein each request includes a request for at least one row from the database object;

(ii) transferring a database command and a rowset parameter indicating a maximum number of rows to return to the server program over the network if the requested row is not maintained by the client program;

(iii) receiving a data block generated by the server program including rows from the database object satisfying the search predicates in response to the database command, wherein the rows included in the data block do not exceed the rowset parameter; and

(iv) returning at least one requested row from the received data block in response to one request for the at least one row of data from the application program.

2. The system of claim 1, wherein the multiple requests specify orientation information for a row from the database object satisfying the specified search predicates.

3. The system of claim 1, wherein the multiple requests received by the client program from the application program comprise single-row fetch requests and the rows from the database object that satisfy the search predicates are returned as part of a scrollable cursor created by the application program.

4. The system of claim 3, wherein the client program further performs:

maintaining a first pointer addressing a last accessed row from the received data block and a client cursor addressing a last requested row from the scrollable cursor; and

incrementing the client cursor to an entry in the database object corresponding to the last row returned to the application program.

5. The system of claim 1, wherein the search predicates are defined with a database cursor that provides a result table subset of the database object that satisfies the search predicates.

6. The system of claim 1, wherein the client program further performs:

determining whether the data block includes less rows than the rowset parameter;

determining a difference between the rowset parameter and a number of rows included in the data block if the data block includes less rows than the rowset parameter; and

sending a command to the server program to transmit the difference of rows.

7. A computer readable storage medium, wherein instructions for a client program capable of communicating with a server program over a network in a distributed database environment are stored in the computer readable storage medium, wherein the distributed database environment includes a database object, wherein the client program is in communication with an application program, and wherein the instructions when executed by a machine performs:

receiving, with the client program, multiple requests for data from the database object satisfying specified search predicates from the application program, wherein each request includes a request for at least one row from the database object;

transferring, with the client program, a database command and a rowset parameter indicating a maximum number of rows to return to the server program over the network if the requested row is not maintained by the client program;

receiving, with the client program, a data block generated by the server program including rows from the database object satisfying the search predicates in response to the database command, wherein the rows included in the data block do not exceed the rowset parameter; and

returning, with the client program, at least one requested row from the received data block in response to one request for the at least one row of data from the application program.

8. The computer readable storage medium of claim 7, wherein the multiple requests specify orientation information for a row from the database object satisfying the specified search predicates.

9. The computer readable storage medium of claim 7, wherein the multiple requests received by the client program from the application program comprise single-row fetch requests and the rows from the database object that satisfy the search predicates are returned as part of a scrollable cursor created by the application program.

10. The computer readable storage medium of claim 9, wherein the instructions when executed by the machine further performs:

maintaining, with the client program, a first pointer addressing a last accessed row from the received data block and a client cursor addressing a last requested row from the scrollable cursor; and

incrementing the client cursor to an entry in the database object corresponding to the last row returned to the application program.

11. The computer readable storage medium of claim 7, wherein the search predicates are defined with a database cursor that provides a result table subset of the database object that satisfies the search predicates.

12. The computer readable storage medium of claim 7, wherein the instructions when executed by the machine further performs:

determining, with the client program, whether the data block includes less rows than the rowset parameter;

determining, with the client program, a difference between the rowset parameter and a number of rows included in the data block ifthe data block includes less rows than the rowset parameter; and

sending, with the client program, a command to the server program to transmit the difference of rows.