The number of connections that can be sustained between a single CICS® region and
the Web is primarily limited by the storage available in the CICS region.The major influences on storage usage for CICS Web support
are:
- Basic storage requirement for each connection. About
4K of storage is required for each connection between CICS and the Web.
- For CICS as an HTTP server: Size of requests received from
Web clients. The total amount of data that CICS accepts for a single request can be limited
by the MAXDATALEN attribute of the TCPIPSERVICE definition.
- The request line and HTTP headers are stored in a temporary storage queue.
- The request body is stored in CICS main storage. Unwanted data from a request
body can be ignored by an application program, but the Web attach task always
reads the complete message in order to clear the data from the socket, and
places all the data in storage.
- Storage used for a request received from a Web client is freed when a
response has been sent to the request.
- For CICS as an HTTP client: Size of responses received from
Web servers. There is no specific way to limit the amount of data that CICS accepts for a response. (The HTTP client facility of CICS Web support
is not designed for use as a browser, so your requests should return only
known resources that you have selected.)
- The status line and HTTP headers are stored in a temporary storage queue.
- The response body is stored in CICS main storage. Unwanted data from a response
body can be ignored by an application program, but the complete message is
read and placed in CICS storage.
- Storage used for responses received from Web servers is required for the
duration of the connection with the Web server. The storage obtained for the
first response is overwritten by each subsequent response that is received
for the connection, or released and re-obtained if a subsequent response requires
a larger amount of storage. The storage is freed when the connection is closed
by the application program using a WEB CLOSE command (or at end of task if
the connection has not previously been closed). The maximum amount of storage
that is obtained for each connection is therefore equal to the size of the
largest message received on the connection.
- For CICS as an HTTP server and CICS as an HTTP client: Size of messages produced
by CICS (requests or responses). While a request or response is being
assembled for sending out from CICS, storage is required for the HTTP headers,
and also for the message body.
- The HTTP headers are stored in a temporary storage queue.
- The message body is stored in CICS main storage.
- Storage used for a request or response sent out from CICS is freed when
the message is sent.
- Code page conversion. Code page conversion can be
carried out for any message body received or sent by CICS, if it is specified
by an application program, analyzer program, or URIMAP definition in the processing
path for the request. The message body is in CICS main storage.
- For conversion between the EBCDIC code page 037 and the ASCII code page
ISO-8859-1, CICS writes the converted message body to the same area of storage as
the original message body, so no additional storage is used.
- For other types of code page conversion, CICS requires additional storage to contain
the converted message body. Depending on the character sets used, the size
of this additional storage area can range from the same size as the original
message body, to a theoretical maximum of four times the size of the original
message body (which is unlikely). For example, 2MB of message body data would
require at least 4MB of storage in total. Double-byte character sets (DBCS)
or multi-byte character sets are likely to require larger storage areas within
this range.

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