SGA_TARGET,SGA_MAX_SIZE and SGA_TARGET vs SGA_MAX_SIZE

SGA_TARGET

SGA_TARGET specifies the total size of all SGA components. If SGA_TARGET is specified, then the following memory pools are automatically sized:

    Buffer cache (DB_CACHE_SIZE)
    Shared pool (SHARED_POOL_SIZE)
    Large pool (LARGE_POOL_SIZE)
    Java pool (JAVA_POOL_SIZE)
   
If these automatically tuned memory pools are set to non-zero values, then those values are used as minimum levels by Automatic Shared Memory Management. You would set minimum values if an application component needs a minimum amount of memory to function properly.

The following pools are manually sized components and are not affected by Automatic Shared Memory Management:

    Log buffer
    Other buffer caches, such as KEEP, RECYCLE, and other block sizes
    Streams pool
    Fixed SGA and other internal allocations

The memory allocated to these pools is deducted from the total available for SGA_TARGET when Automatic Shared Memory Management computes the values of the automatically tuned memory pools.

SGA_MAX_SIZE

SGA_MAX_SIZE specifies the maximum size of the SGA for the lifetime of the instance.

     Initial size of SGA at startup, dependent on the sizes of different pools in the SGA, such as buffer cache, shared pool, large pool, and so on.

SGA_TARGET vs SGA_MAX_SIZE

SGA_MAX_SIZE sets the overall amount of memory the SGA can consume but is not dynamic. SGA_TARGET, a new 10g feature used for Automatic Shared Memory Management allows for dynamic resizing of SGA
SGA_MAX_SIZE parameter is the max allowable size to resize the SGA Memory area parameters. If the SGA_TARGET is set to some value then the Automatic Shared Memory Management (ASMM) is enabled, the SGA_TARGET value can be adjusted up to the SGA_MAX_SIZE parameter, not more than SGA_MAX_SIZE parameter value.
i.e. If SGA_MAX_SIZE=4GB and SGA_TARGET=2GB, later period of time, if you want you can resize your SGA_TARGET parameter to the value of SGA_MAX_SIZE i.e. 4GB, you can't resize the SGA_TARGET value to more than 4GB.
Usually, sga_max_size and sga_target will be the same value, but there may be times when you want to have the capability to adjust for peak loads. By setting the Oracle sga_max_size parameter higher than sga_target, you allow dynamic adjustment of the sga_target parameter.

Note that sga_max_size is for Oracle 10g only, and in 11g and beyond, Oracle automatic memory management is configured using the memory_target  and memory_max_target initialization parameters.  The memory_target parameter specifies the amount of shared memory available for Oracle to use when dynamically controlling the SGA and PGA. The memory_max_target AMM parameter specifies the max size that memory_target may take.
You can enable and disable AMM by changing the value of these parameters to non-zero settings:
    sga_target
    sga_max_size
    pga_aggregate_target
    sga_max_size

Forms Servlet or Socket Mode

Many products within the Oracle E-Business Suite have screens that are built with Oracle Forms.  Oracle Forms can be run in either servlet mode or socket mode.  Apps 11i is based on Forms 6i and is configured to run in socket mode by default.  Apps 12 is based on Forms 10g and is configured to run in servlet mode by default.

Forms Servlet Mode

The Forms Listener Servlet is a Java servlet that delivers the ability to run Oracle Forms applications over HTTP and HTTPS connections. It manages the creation of a Forms Server Runtime process for each client, as well as network communications between the client and its associated Forms Server Runtime process.

The desktop client sends HTTP requests and receives HTTP responses from the web server. The HTTP Listener on the web server acts as the network endpoint for the client, keeping other servers and ports from being exposed at the firewall.

Forms Socket Mode

Initial releases of the Oracle Forms Server product used a simple method for connecting the client to the server. The connection from the desktop client to the Forms Listener process was accomplished using a direct socket connection.  The direct socket connection mode was suitable for companies providing thin client access to Forms applications within their corporate local area networks. For the direct socket connection mode, the client had to be able to see the server and had to have permission to establish a direct network connection.

Although the direct socket connection mode is perfectly suited for deployments within a company’s internal network, it's not the best choice for application deployment via unsecured network paths via the Internet. A company connected to the Internet typically employs a strict policy defining the types of network connections that can be made by Internet clients to secure corporate networks. Permitting a direct socket connection from an external client exposes the company to potential risk because the true identity of the client can be hard to determine.

Servlet Mode Advantages

    HTTP and HTTPS traffic is easily recognizable by routers, while socket mode communications is generally considered suspect and treated on an exception basis.
    Existing networking hardware can be used to support basic functions such as load-balancing and packet encryption for network transit.
    More resilient to network and firewall reconfigurations.
    More robust: servlet connections can be reestablished if network connections drop unexpectedly for Forms, Framework, and JSP-based pages.
    Is the only supported method for generic Oracle Forms customers, and therefore is more thoroughly tested by the Forms and E-Business Suite product groups.
    Performance traffic can be monitored via tools like Oracle Real User Experience Insight (RUEI).
    Socket mode is not supported on Windows-based server platforms.

Socket Mode Advantages

    Uses up to 40% less bandwidth than Forms servlet mode.  This may be perceived by Wide Area Network (WAN) users as causing slower responsiveness, depending upon network latency.
    Uses fewer application-tier JVM resources than servlet mode, due to fewer TCP turns and lack of overhead associated with HTTP POST handling.

Switching Apps Deployments Between Modes

Due to its numerous advantages, Forms servlet mode is the preferred and recommended deployment model for Forms on the web.

There may be circumstances where you need to switch between the default Forms modes.  You might wish to switch your Oracle E-Business Suite Release 12 environment to socket mode to improve performance or reduce network load.  You might wish to switch your Apps 11i environment to servlet mode as part of your rollout to external web-based end-users outside of your organization.

If you're running Apps 11i and would like to switch to servlet mode, see:

    Using Forms Listener Servlet with Oracle Applications 11i (Note 201340.1)

If you're running Apps 12 and would like to switch to socket mode, see:

    Using Forms Socket Mode in Oracle Applications Release 12 (Note 384241.1)