Storage considerations

If you are working with large Db2® tables or views, you may need to consider how much space is required in the editor to store the copy of the Db2® object.

The FM/Db2 editor uses storage in the TSO user's address space. The size of the address space is governed by the TSO region size, which may be limited by your systems administrator. As a guide, the amount of space needed by the FM/Db2 editor is the number of rows loaded, multiplied by the number of bytes of data in each row, multiplied by an editor overhead.

For example, to load 100,000 rows of 20 bytes into the FM/Db2 editor, requires at least 2MB of storage. The editor overhead factor is at least 1 and can be as much as 3, so up to 6MB of storage may be needed.

To take another example, if each row occupies 1000 bytes, every 1024 rows loaded requires about 1MB of storage. Therefore to load 100,000 such rows, at least 100MB of storage is required.

When the editor is operating in "normal mode", the number of rows loaded remains fixed and can be used to estimate the total storage requirements.

When the editor is operating in "large mode", the number of rows loaded in approximately three times the number of rows visible in TABL display format. This number remains unchanged regardless of any scrolling operations. When changes are made to rows, those rows remain in the editor. Therefore you may still encounter storage problems if you perform edit operations that change large numbers of rows in the table.

When you need to change large numbers of rows, consider changing the table by direct execution of SQL statements.