Performance Tuning for Content Manager

Chapter 8. Tuning DB2 for Content Manager 237

8.6.29 Application support layer heap size (ASLHEAPSZ)

Impact

DBM - High

Description

The application support layer heap represents a communication buffer between

the local application and its associated agent. This buffer is allocated as shared

memory by each database manager agent that is started. It is freed when the

database agent process is terminated.

If the request to the database manager or its associated reply do not fit into the

buffer, they will be split into two or more send-and-receive pairs. The size of this

buffer should be set to handle the majority of requests using a single

send-and-receive pair. The size of the request is based on the storage required

to hold:

 The input SQLDA

 All of the associated data in the SQLVARs

 The output SQLDA

 Other fields that do not generally exceed 250 bytes

In addition to this communication buffer, this parameter is used for two other

purposes:

 It is used to determine the I/O block size when a blocking cursor is opened.

This memory for blocked cursors is allocated out of the application’s private

address space, so you should determine the optimal amount of private

memory to allocate for each application program. If the database client cannot

allocate space for a blocking cursor out of an application’s private memory, a

non-blocking cursor will be opened.

 It is used to determine the communication size between agents and db2fmp

processes. (A db2fmp process can be a user-defined function or a fenced

stored procedure.) The number of bytes is allocated from shared memory for

each db2fmp process or thread that is active on the system.

The data sent from the local application is received by the database manager

into a set of contiguous memory allocated from the query heap. The

ASLHEAPSZ parameter is used to determine the initial size of the query heap

(for both local and remote clients). The maximum size of the query heap is

defined by the QUERY_HEAP_SZ parameter.

Default values (range)

15 (1 - 524,288) 4-KB pages