VSAM DB2 and number of extent



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VSAM DB2 and number of extent

Postby samb01 » 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


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 :


     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...
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Re: VSAM DB2 and number of extent

Postby NicC » Thu Oct 31, 2019 4:11 pm

Not a DB2 question. Topic moved.
The problem I have is that people can explain things quickly but I can only comprehend slowly.
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Re: VSAM DB2 and number of extent

Postby Robert Sample » 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?
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Re: VSAM DB2 and number of extent

Postby samb01 » 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.
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Re: VSAM DB2 and number of extent

Postby enrico-sorichetti » 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
cheers
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Re: VSAM DB2 and number of extent

Postby samb01 » Mon Nov 04, 2019 1:06 pm

UT40.LISTCAT.txt
Hello, here is a listcat ALL of the db2 vsam :
You do not have the required permissions to view the files attached to this post.
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Re: VSAM DB2 and number of extent

Postby NicC » Tue Nov 05, 2019 1:26 am

Please do not post attachments - a cut and paste will do (using the code tags of course)
The problem I have is that people can explain things quickly but I can only comprehend slowly.
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Re: VSAM DB2 and number of extent

Postby prino » Tue Nov 05, 2019 2:49 am

And you really want us to do something with it? You've got to be flucking kidding...
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Re: VSAM DB2 and number of extent

Postby willy jensen » 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) ?
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Re: VSAM DB2 and number of extent

Postby samb01 » 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 :


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