Many ISPF users are prompted for what they should do with their LOG-dataset when they leave ISPF. And the most used answer is: Delete it. Some ISPF users has found out how they make ISPF do the delete automatically, but only a very small group of persons know how to avoid the LOG-dataset totally. You don't need to allocate it unless you have to use its contens.

So what do you need the LOG-dataset for? What does ISPF use it for? The usage depends a lot on how ISPF is started. Normally ISPF only writes to the LOG-dataset when an ISPF service ends with a return code greater than 8 and you are using CONTROL ERRORS CANCEL (the default when starting ISPF). Besides this situation the LOG-dataset is only used when you choose to send information to it. For instance the ISPF trace facility sends its output to the LOG-dataset. In other words the LOG-dataset only contains valid information when you have chosen to use it, while the default is to use it only in error situations which ISPF has its own way of dealing with.

Now you can decide if you want to get totally rid of the LOG-dataset. You can always switch it on again if you need it. On the ISPF main menu you select item 0 for ISPF-defaults. On the ISPF-defaults menu you select item LOG/LIST defaults. On the LOG/LIST defaults panel there are two columns. Left column describes the LOG-dataset and the right column describes the LIST-dataset. In the left column there is a field called "Primary pages". Set this field to 0 (zero) and leave the LOG/LIST defaults panel using F3 (END). Just ignore the text in the lower left corner saying something like *** LOG dataset already allocated ***. It only tells you that the change you just have made takes effect from the next log on to ISPF. So now you leave ISPF normally and log on to ISPF again.

If you eventually one day need to use the LOG-dataset you allocate it by altering the value of field "Primary pages" to a number greater than zero, for instance the same value as in field "Secondary pages". Then you without hesitation log off your ISPF session and log on to it again. You can use the ISPF-command LOG to free your currently allocated LOG dataset and allocate a new one, so that you can study the contens of the original LOG-dataset while running ISPF. Of cource this will only work when the LOG-dataset is allocated.