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What's the rule of DB2 D/S allocation?

 
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dejunzhu

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Joined: 08 May 2008
Posts: 390
Location: China

PostPosted: Sat Nov 28, 2009 5:37 pm    Post subject: What's the rule of DB2 D/S allocation?
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According the D/S allocation description in IBM DB2 manual:<<DB2 V9.1 Administration Guide>> P23, it says:
Quote:
The correct format for the name of a data set is as follows:
catname.DSNDBx.dbname.psname.y0001.znnn
...
znnn:
For simple or segmented table spaces, the number is 001 (preceded by A)
for the first data set. When little space is available, DB2 issues a warning
message. If the size of the data set for a simple or a segmented table space
approaches the maximum limit, define another data set with the same
name as the first data set and the number 002. The next data set will be
003, and so on.

Please allow me to ask the following 2 quesitons:
1. what does maximum limit refer to? Does it refer to the extents limit on ONE volumn or total volumns? Extents limit description

2. One of my tablespace has the following DB2 D/S allocated:
Code:

TABLESPACE&#12288;EXTENSITION&#65306;67
 Total Tracks:      139425 non-x:     139425   Data Sets:      4 non-x:      4 
 -------------------------------------------------------------------------------
 Command - Enter "/" to select action                        Tracks %Used   XT 
 -------------------------------------------------------------------------------
          DC10IV.DSNDBD.DC10D001.DC10SDS1.I0001.A001          43695    ?    21 
          DC10IV.DSNDBD.DC10D001.DC10SDS1.I0001.A002          43695    ?    21 
          DC10IV.DSNDBD.DC10D001.DC10SDS1.I0001.A003          43695    ?    21 
          DC10IV.DSNDBD.DC10D001.DC10SDS1.I0001.A004           8340    ?     4 
 ***************************** End of Data Set list ****************************


Can you explain why there are 4 D/S in all? Isn't this conflicting with the description in DB2 manual beforementioned?
Since the total extents is 67, why 4 D/S was allocated?

While some other table has D/S allocation like this:
Code:

 
EXT               DATA SET NAME                                                                                                     
----------------------------------------------------------------------                                                               
140   DC10CV.DSNDBD.DC10D001.DC10XLOB.I0001.A001                                                                                   
117   DC10CV.DSNDBD.DC10D001.DC10SRP0.I0001.A001

If a DB2 D/S can just be allocated to ONE volumn, there must cann't be a extent of 140.
That's to say, one D/S(here is DC10CV.DSNDBD.DC10D001.DC10XLOB.I0001.A001 ) is allocated on multiple volumns.

Appreciate your kind help very much!
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Robert Sample

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PostPosted: Sat Nov 28, 2009 7:13 pm    Post subject:
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I am not a DB2 person, but I can give you this:

1. Maximum limit has nothing to do with extents. The context makes it clear the reference is to size (tracks in your example). A 3390-3 has 50050 tracks, so getting close to that size will trigger the new file creation (for some value of "close".

2. I suspect that DB2 is using 15% of the disk pack as the trigger point, so whenever a data base gets to 43695 tracks another file is allocated. The primary and secondary space allocations would control this, not the number of extents allocated.

3. There's not enough data provided to know what is going on -- do a LISTCAT of DC10CV.DSNDBD.DC10D001.DC10XLOB.I0001.A001 and post it.
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dejunzhu

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Joined: 08 May 2008
Posts: 390
Location: China

PostPosted: Sun Nov 29, 2009 7:14 am    Post subject:
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Robert Sample wrote:
I am not a DB2 person, but I can give you this:

1. Maximum limit has nothing to do with extents. The context makes it clear the reference is to size (tracks in your example). A 3390-3 has 50050 tracks, so getting close to that size will trigger the new file creation (for some value of "close".

2. I suspect that DB2 is using 15% of the disk pack as the trigger point, so whenever a data base gets to 43695 tracks another file is allocated. The primary and secondary space allocations would control this, not the number of extents allocated.

3. There's not enough data provided to know what is going on -- do a LISTCAT of DC10CV.DSNDBD.DC10D001.DC10XLOB.I0001.A001 and post it.


I think I have found the rule for D/S allocation:
Every D/S has a maximum size of 43695 tracks. If size surpasses it, a new D/S is allocated.

But I wonder, is this rule set by DB2, or system?
If it is set by DB2, where is the related information on manual?
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Robert Sample

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PostPosted: Sun Nov 29, 2009 7:28 am    Post subject:
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I recommend you contact your site DB2 support group for assistance. They are the ones who installed DB2, so they should know what the system and site default values are.
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dejunzhu

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Joined: 08 May 2008
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Location: China

PostPosted: Sun Nov 29, 2009 7:57 am    Post subject:
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By the way, many thanks to Robert. LISTCAT command provided me an effective way to analyse statistics for DB2 D/S, such as , how is secondary space allocated? (Because I set SEQTY=-1, which refers to default value of DB2, I cannot check the value via SQL statements against catalog tables.)
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