Compress Vsam Dataset

elonics · New User Joined: 05 Jul 2005 Posts: 49 Location: India

Hi ALL,
Can we compress the vsam dataset if it is out of space. How can we do this.

elonics · New User Joined: 05 Jul 2005 Posts: 49 Location: India

This is a interview question for my friend in IBM. Can we compress it or not. or Did any faced a problem when VSAM is out of space.

superk · Posted: Tue Aug 16, 2005 7:44 pm

Virtually all VSAM datasets will already be compressed with SMS compression routines. So, if it is not already, yes, it can be. If it is already, then all that can be done is to either free up some space by eliminating or moving old data, or by actually increasing the storage requirements.

shivashunmugam Muthu · Posted: Wed Aug 17, 2005 9:25 am

Hi SuperK

How to compress it? Is it like something which we used to compress PDS & PS in left extreme as "C"?

am jus searching whether am having any VSAM file...I dint get yet..will try that one...but b4 that please update me..

elonics · New User Joined: 05 Jul 2005 Posts: 49 Location: India

hi Superk,
can u be mor specific in ur answer. i could nt get u .

shivashunmugam Muthu · Posted: Wed Aug 17, 2005 4:27 pm

NOT 'C' .....Its 'Z'

Bit Confused!

sarath_ibm · New User Joined: 03 Aug 2005 Posts: 14 Location: hyderabad

hi elonics . its very simple type z in leftside . it will get compressed.

elonics · New User Joined: 05 Jul 2005 Posts: 49 Location: India

I KNOW ,SARATH,THSI IS OK FOR FLATFILES . CAN THIS BE APPLICABLE FOR VSAM DATASETS

Ravi Gopal · New User Joined: 04 Aug 2005 Posts: 3

Hi,

To avoid this out of space condition of vsam dataset, you need to do REORG.It can be done in the following ways:

Way1:
====
1.Unload the data from VSAM to falt file using REPRO.
2.Then allocate more volumes for the VSAM file using IDCAMS in batch.
3.Then reload the VSAM file from flat file again using REPRO.

Way2:
====
1.You can directly alter the VSAM file using the following command:
//STEP01 EXEC PGM=IDCAMS
//SYSPRINT DD SYSOUT=*
//SYSUDUMP DD SYSOUT=*
//SYSIN DD *
ALTER VSAM.DATASET ADDVOLUMES(* * * * *)
/*

This will add 5 new candidate volumes to the file and will be taken care by SMS.

*Sometime it may not allow us to do this due to clients restriction on using the space.

Regards
Ravi

shivashunmugam Muthu · Posted: Thu Aug 18, 2005 12:36 pm

hi Ravi

your options are perfect.. But how to compress is the question here. Adding space is something which we do later.....(after all options)

we cud compress by issuing 'z' only with PDS.

For PSDS/VSAM we cant?

any options guyz

elonics · New User Joined: 05 Jul 2005 Posts: 49 Location: India

Thanx Ravi

mmwife · Super Moderator Joined: 30 May 2003 Posts: 1592

I've used DFSORT copy to reorg a vsam file. The seq is:

sort/copy to flat file; delete/define VSAM file; sort/copy to empty VSAM file.

As I recall, what you buy back is the freespace and the partially filled CI/CAs The used freespace is freed but the primary space is used in its stead; really not a savings.

The advantage is supposed to be better performance because the split processing overhead is avoided.

ideas · New User Joined: 25 May 2005 Posts: 52 Location: India

Compression isnt feasible for VSAM I guess.

dneufarth · Posted: Tue Aug 23, 2005 1:35 am

Products are available from CA and BMC that compress VSAM datasets.

Dave

sendil · New User Joined: 30 Jun 2005 Posts: 27

When data is compressed, the length of a stored record may change after
an update without any logical record length change.
VSAM compression is done transparently to the application, through the data
class (DC) parameter in SMS data sets. This DC assigned to the data set has
to specify the following DSNTYPE=EXT with a required COMPACTION=Y
(blank defaults to N). The following screen pictures the ISMF list of the DC:

VSAM compression only applies to KSDS in extended format. All the fields to
the left of the key in the logical record are not compressed. In your next data
model, you can define the key field with offset equal to zero.
Compression affects the catalog, VTOC, and SMF information about VSAM
data sets.
DATACLAS EXTENDED MEDIA
NAME DATA SET NAME TYPE ADDRESSABILITY COMPACTION TYPE
--(2)--- -------(26)------- -----(27)----- ---(28)--- -(29)-
DCSMB EXTENDED REQUIRED NO ---- ------
DCSTRIPE EXTENDED REQUIRED NO ---- ------
DCXXXX EXTENDED REQUIRED NO ---- ------
DIRECT ------------------ NO ---- ------
ECCST ------------------ NO YES MEDIA2
EHPCT ------------------ NO YES MEDIA3