IBM Mainframe Forum

Posted: **Thu Oct 31, 2019 3:34 pm**

Hello,

i can't anderstand the number of extent of this DB2 VSAM :

Command - Enter "/" to select action                        Tracks %Used   XT 
------------------------------------------------------------------------------
         DB2REEL.DSNDBD.DBRL.TSN973RL.I0001.A003             87375    ?   163 
 

in five volumes

Select all

DB2REEL.DSNDBD.DBRL.TSN973RL.I0001.A003             23865    ?    44
DB2REEL.DSNDBD.DBRL.TSN973RL.I0001.A003              4515    ?    47
DB2REEL.DSNDBD.DBRL.TSN973RL.I0001.A003             26790    ?    42
DB2REEL.DSNDBD.DBRL.TSN973RL.I0001.A003             25185    ?    27
DB2REEL.DSNDBD.DBRL.TSN973RL.I0001.A003              7020    ?     3
 

A listcat of this VSAM :

Select all

     ALLOCATION                                                                
       SPACE-TYPE------CYLINDER     HI-A-RBA------4294656000                   
       SPACE-PRI--------------2     HI-U-RBA------4293906432                   
       SPACE-SEC--------------1                                                
     VOLUME                                                                    
       VOLSER------------PDBDJ0     PHYREC-SIZE---------4096     HI-A-RBA------
221921280     EXTENT-NUMBER---------47                                         
       DEVTYPE------X'3010200F'     PHYRECS/TRK-----------12     HI-U-RBA------
221921280     EXTENT-TYPE--------X'40'                                         
       VOLFLAG------------PRIME     TRACKS/CA-------------15                   
       EXTENTS:                                                                
       LOW-CCHH-----X'03120000'     LOW-RBA----------------0     TRACKS--------
-------30                                                                      

 

So i guess it is allocated with : SPACE=(CYL,(2,1))

So to reach 87375 TRACKS with 123 EXTENT, the allocation SPACE=(CYL,(2,1)) is not enought...

my calcul is that :

2 CYLS * 5 VOLUMEs = 10 CYLS = 150 TRACKS n(corresponding to the primary allocation in each volume)

and

1 CYL * (163 - 5) = 158 CYL (163 is the number of extent et 5 the primaray ectent in each volume).

So we have : 158 CYLS + 10 CYLS = 2520 TRACKS

and the dataset has : 87375 TRACKS

So i can't anderstand the difference...

Posted: **Thu Oct 31, 2019 4:11 pm**

Not a DB2 question. Topic moved.

Posted: **Fri Nov 01, 2019 2:42 am**

So i guess it is allocated with : SPACE=(CYL,(2,1))

This is true only if you're not using an SMS data class. Perhaps if you had given us the entire LISTCAT output, we could tell you more. But with what you've given us so far, about all we can tell you is that the size of the data set does not correlate to the IDCAMS allocation -- but who knows why?

The larger question is why do you care? As long as the data set is allocated appropriately, and the data base is not having size issues, why should ANYONE care?

Posted: **Fri Nov 01, 2019 3:08 am**

We care because or the db2 optimization. The more extent there are the worst the performance is in DB2.
on monday i will give you the entire listcat. But it seems that db2 allocate itself the vsam dataset throu the create table.

Posted: **Fri Nov 01, 2019 3:47 am**

about all we can tell you is that the size of the data set does not correlate to the IDCAMS allocation

probably because ONLY the info about extent number 47 was posted

Posted: **Mon Nov 04, 2019 1:06 pm**

UT40.LISTCAT.txt

Hello, here is a listcat ALL of the db2 vsam :

Posted: **Tue Nov 05, 2019 1:26 am**

Please do not post attachments - a cut and paste will do (using the code tags of course)

Posted: **Tue Nov 05, 2019 2:49 am**

And you really want us to do something with it? You've got to be flucking kidding...

Posted: **Tue Nov 05, 2019 4:03 am**

And what result do you get when adding all the extents (I'm not gonna do it either) ?

Posted: **Tue Nov 05, 2019 1:44 pm**

DBA Admin told me it's not possible to reduce the extent because it's DB2 wich choose itself the secondary allocation.
Db2 dosen't care about the create table :

Select all

CREATE TABLESPACE TSN973RL   
       IN DBRL               
       USING STOGROUP SGRL   
           PRIQTY 1000       
          SECQTY 100        
 

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