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* PTF CD602.T06                                        Jan 1994 *               

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* Keywords : STORAGE STARTUP ABENDS TECH NOTE T9306220          *               

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* DB-90S RELEASE 4.2 TAPES : C60201                             *               

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* This technical note describes storage usage by the DB90s      *               

* software and how to minimize abends at startup.               *               

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In order to minimize abends at startup this Tech Note explains what             

happens at startup when you have DB90s installed.                               

                                                                                

The DB90s software is automatically loaded at startup when                      

IDMSDBIO is first called. DB90s attempts to load all of its modules,            

regardless of the components you have activated.                                

                                                                                

Because virtually all DB90s modules are involved with file                      

activities and the manipulation of MVS DCB control blocks, there is             

an MVS limitation regarding BDAM DCBs such that the programs have               

to be loaded below the 16 megabyte line in 24-bit storage.                      

                                                                                

These DB90s modules occupy 90 kilobytes of the 24-bit private area.             

These modules have to be loaded immediately at startup, therefore               

this storage comes from the FREESTG ammount returned to MVS.                    

                                                                                

At DB90s initialisation time, certain DB90s control blocks have                 

to be built for each file that is under DB90s control. These include            

all files defined to Sequential PreFetch, and all files in buffers              

defined to MEGABUF. Again some of these control blocks contain DCBs and         

have to  reside in 24-bit storage.                                              

                                                                                

For each file under DB90s control 221 bytes are required below-the-line.        

                                                                                

Depending on whether a warmstart is performed affects when these file           

control blocks are built.                                                       

                                                                                

At CV startup, after a clean shutdown (ie no warmstart), these file             

control blocks will be built after the basic system has been                    

initialised, and the remaining storage has been returned to MVS.                

These control blocks will therefore be GETMAINED from this storage              

returned to MVS.                                                                

                                                                                

However, if the CV performs a warmstart, then the DB90s file control            

blocks are built during the warmstart process when the files are                

opened and before the storage has been returned to MVS. In this                 

case they will be GETMAINED from the FREESTG that was returned                  

to MVS at CV startup.                                                           

                                                                                

CA Tech Note 90-04-1010 recommends that FREESTG should be closely tuned         

to the value of Storage Returned to OPSYS. If you have done this, then          

there should be no problems with DB90s at CV startup, as there will be          

sufficient storage returned with the FREESTG parameter of #DCPARM.              

                                                                                

Sites that have tightly tuned their FREESTG parameter and REGION SIZE,          

may therefore experience problems during CV startup with INSUFFICIENT           

STORAGE messages or GETMAIN failures.                                           

                                                                                

If these occur after the remaining storage has been returned to MVS,            

then increase the job's REGION SIZE.                                            

                                                                                

If the problems occur during warmstart or before remaining storage              

gets returned to MVS, then you need to increase your FREESTG                    

parameter.                                                                      

                                                                                

You should be aware that if your system starts cleanly without a                

warmstart, this does not automatically mean that everything will be             

OK during a warmstart. If your FREESTG parameter is too small, then             

when a warmstart is required there may be insufficient storage to               

build the file control blocks.                                                  

                                                                                

We therefore recommend you test the warmstart process after installing          

DB90s, to check your FREESTG parameter is sufficient.                           

                                                                                

Remember to calculate storage required by DB90s;                                

                                                                                

       90k  +  ( 221 bytes  x  No. of files under DB90s control )               

                                                                                

For further information and discussion on the use of storage during             

CV startup, see CA Tech Note: 90-04-1010.