Patent Application
20050144276
The present invention relates to the processing of application server requests in database systems, and more particularly to the processing of multiple application server requests multiplexed over a single database connection.
When the application 103 issues a request to the database server 102, the statement is sent with parameters, including a package name, a consistency token, and a section number. The database engine at the database server 102 prepares to execute the statement by creating data structures that represent the package and the section number. The consistency token helps to maintain consistency between the data structures that were created and the application that is being executed. The package name identifies the application source and the statements contained therein. Application sources are programs or sub-programs. A section number is assigned to each unique statement in the package and serves to associate the statement with the corresponding data structures at the database server 102.
However, a problem with the conventional system is section collision, where the section identifier for multiple statements sent over a single database connection is identical. Such section collision results when multiples of the same statement are sent over a single database connection. In this situation, section collision occurs in several ways: (1) multiples of the same statement are sent over a single database connection from different application sources within the same application; (2) a single statement containing multiple application sources is sent; (3) multiples of the same statement from different applications are multiplexed over a single database connection; and (4) multiple open cursor statements for the same cursor are sent over a single database connection.
To illustrate section collision due to multiples of the same statement sent from different application sources within the same application over a single database connection, assume that two different application sources within the same application 103 issues a “CALL SP1” over the same database connection. Both of these statements would have identical package names and section numbers since they contain the same statements.
To illustrate section collision due to a single statement containing multiple application sources being sent over a database connection, assume that the application 103 sends the following statement: “SELECT UDF1(x), UDF2(x), UDF3(x) FROM T1”. If all three UDF's are written in Java, each of these UDF's can be executed in its own JVM environment on an intermediate server which is unaware of any other JVM, and with all three JVM's being multiplexed through a single database connection to the database server 102. Because all three UDF's are executing the same package and statements, each JVM may issue a prepare using an identical section within the package, causing collision with one another.
To illustrate section collision due to multiples of the same statement from different applications multiplexed over a single database connection, assume that a first application issues an “OPEN C1” statement over a connection, and a second application issues an “OPEN C1” statement over the same connection. Both of these statements would have the same package name and section number, resulting in section collision. Conventionally, to avoid this problem, the two statements would be issued using separate threads or connections. This prevents the bandwidth of the connection from being fully utilized.
Section collision due to multiple open cursor statements for the same cursor sent over a single database connection results from the restriction of conventional database systems that there can be only one instance of an open cursor of a specific name at the same processing, or nesting level, within an application. For example, assume that the application 103 issues the statement, “OPEN C1”, to the database server 102 to open the cursor named “C1”. The database server 102 then creates control structures 104 representing the package, the section, and any other needed runtime structures for the statement. But, if the application 103 issues another “OPEN C1” statement, using the same database connection, before the first open cursor closes, then an error occurs. The second open cursor statement would have the same section number as the first open cursor statement. To process both open cursors would result in section collision.
Some database systems would allow the second invocation, but would also close the first open cursor, losing all information from the first open cursor. Other database systems would keep the first cursor information, but would refuse to allow the second cursor to be opened. Still other database systems would use separate threads or remote connections between the application server 101 and the database server 102 to separate the application into multiple processes. This latter approach, however, has a significantly negative impact on performance.
Accordingly, there exists a need for a method and system for uniquely identifying application server requests multiplexed over a single database connection. The present invention addresses such a need.
In a method and system for avoiding section collision for application server requests over a single database connection, the database server assigns query identifiers to each instance of the same cursor opened for the same processing level within an application, allowing multiple instances of the same cursor to be processed in parallel without section collision. The application server assigns a command source identifier to each statement sent over a single database connection to uniquely identify the application source of the statement. This applies for multiples of the same statement sent by different application sources within the same application, for a single statement containing multiple application sources, and for multiple query statements from different applications multiplexed over a single database connection. These statements can be processed separately from and in parallel with the each other without section collision.
The present invention provides a method and system for uniquely identifying application server requests multiplexed over a single database connection. The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Various modifications to the preferred embodiment will be readily apparent to those skilled in the art and the generic principles herein may be applied to other embodiments. Thus, the present invention is not intended to be limited to the embodiment shown but is to be accorded the widest scope consistent with the principles and features described herein.
In the method and system in accordance with the present invention, the application server assigns a command source identifier to each statement sent over a single database connection to uniquely identify the application source of the statement. The command source identifier uniquely identifies the application source for multiples of the same statement sent by different application sources within the same application, the application sources for a single statement containing multiple application sources, and the application sources for multiple statements from different applications multiplexed over a single database connection. These statements can be processed separately from and in parallel with the each other without section collision. Further, the database server assigns query identifiers to each instance of the same cursor opened for the same processing level within an application.
To more particularly describe the features of the present invention, please refer to
When multiple open cursor statements for the same cursor in a single application source are sent over a single database connection, the use of the command source identifier does not avoid section collision. In this situation, both open cursor statements would have the same command source identifier, as they are from the one application source. To address this problem, the present invention assigns unique query identifiers to each instance of the same cursor opened for the same processing level within an application.
A “duplicate query allowed” (DQA) parameter can be provided in conjunction with the query identifier to allow backward compatibility to existing database systems. The DQA parameter signifies that the requesting system allows duplicates instances of the same cursor to be created for the same application source. This provides the requester an option to allow duplicate cursor instances or not. When the application server sends the second statement to open the same cursor, and the DQA parameter is set to TRUE for the second statement, then the database server 302 will create the second instance 702 of the cursor and return the second query identifier. However, care should be taken that the open cursor statements are not executed in an infinite loop. Otherwise, the database system will continually create new instances of the same cursor, resulting in a flooding of the database memory.
The query identifier and the command source identifier can be used separately or in combination. For example, as illustrated in
A method and system for avoiding section collision for application server requests over a single database connection have been disclosed. In the method and system, the database server assigns query identifiers to each instance of the same cursor opened for the same processing level within an application. This allows multiple instances of the same cursor to be processed in parallel without section collision. In the method and system, the application server assigns a command source identifier to each statement sent over a single database connection to uniquely identify the application source of the statement. The command source identifier uniquely identifies the application source for multiples of the same statement sent by different application sources within the same application, the application sources for a single statement containing multiple application sources, and the application for multiple statements from different applications multiplexed over a single database connection. These statements can be processed separately from and in parallel with the each other without section collision.
Although the present invention has been described in accordance with the embodiments shown, one of ordinary skill in the art will readily recognize that there could be variations to the embodiments and those variations would be within the spirit and scope of the present invention. Accordingly, many modifications may be made by one of ordinary skill in the art without departing from the spirit and scope of the appended claims.
