Stream size

This fullword contains the length of the stream (in hexadecimal). It is the total number of bytes available in the stream for text. A stream wraps if the maximum number of bytes has been reached and the stream is defined as one that can wrap. The bit setting for the stream flags in byte eight determines the ability of a stream to wrap.

Stream management overhead can be determined by using the following formula:

number of lines per index descriptor block   + 1
  maximum number of lines in the stream

Index Descriptor Blocks (IDBs) are part of an indexing mechanism Session Manager uses for referencing stream data.

For example, you can determine the number of bytes of stream management overhead for the SMOUT stream as follows. This stream is defined as 4096 bytes long, 150 lines maximum, and 5 lines per IDB. Using the above formula results in the following:

150 + 1 = 30 + 1 = 31 IDBs
 5

The 31 IDBs can actually index 155 lines of data. Using the QUERY.STREAMS command with the IBM-supplied defaults would show this.

Because IDBs are eight bytes long, the overhead is:

31 IDBs x 8 bytes per IDB = 248 bytes overhead

Thus, 248 bytes of stream management overhead are obtained in addition to the text portion size. The two physical storage requirements really define one logical stream consisting of an overhead area and a text area.

For a discussion of IDBs and performance considerations, see Changing the number of lines per IDB.