HTTP Session Size and Scope (Sun GlassFish Enterprise Server 2.1 Deployment Planning Guide)

Sun GlassFish Enterprise Server 2.1 Deployment Planning Guide

HTTP Session Size and Scope

The session size per request depends on the amount of session information stored in the session.

Tip –

To improve overall performance, reduce the amount of information in the session as much as possible.

It is possible to fine-tune the session size per request through the persistence scope settings. Choose from the following options for HTTP session persistence scope:

session: The server serializes and saves the entire session object every time it saves session information to HADB.
modified-session: The server saves the session only if the session has been modified. It detects modification by intercepting calls to the bean’s setAttribute() method. This option will not detect direct modifications to inner objects, so in such cases the SFSB must be coded to call setAttribute() explicitly.
modified-attribute: The server saves only those attributes that have been modified (inserted, updated, or deleted) since the last time the session was stored. This has the same drawback as modified-session but can significantly reduce HADB write throughput requirements if properly applied.

To use this option, the application must:

Call setAttribute() or removeAttribute() every time it modifies session state.
Make sure there are no cross references between attributes.
Distribute the session state across multiple attributes, or at least between a read-only attribute and a modifiable attribute.

The following table summarizes the advantages and disadvantages of the persistence scope options.

Table 2–2 Comparison of Persistence Scope Options


Persistence Scope Option	Advantages	Disadvantages
modified-session	Provides improved response time for requests that do not modify session state.	During the execution of a web method, typically `doGet()` or `doPost(`), the application must call a session method: `setAttribute()` if the attribute was changed `removeAttribute()` if the attribute was removed.
session	No constraint on applications.	Potentially poorer throughput and response time as compared to the `modified-session` and the `modified-attribute` options.
modified-attribute	Better throughput and response time for requests in which the percentage of session state modified is low.	As the percentage of session state modified for a given request nears 60%, throughput and response time degrade. In such cases, the performance is worse than the other options because of the overhead of splitting the attributes into separate records.