Free space in compression calculations on table space
The DSN1COMP utility considers the PCTFREE and FREEPAGE values when making compression estimates unless the input data set is a LOB table space or image copy data set of a LOB table space. The PCTFREE and FREEPAGE values do not apply to LOBs.
DSN1COMP reports the PCTFREE and FREEPAGE values used and the amount of uncompressed data, as shown in the following examples. Note that if you specify PCTFREE or FREEPAGE values for DSN1COMP that are different than the values that were specified in the SQL to create or alter the table space, the DSN1COMP output includes a different value for uncompressed pages.
The following example shows the DSN1COMP output for compressed data:
DSN1998I INPUT DSNAME = DB2SMS.DSNDBC.DSN03686.ZZINSRZY.I0001.A001 , VSAM
DSN1944I DSN1COMP INPUT PARAMETERS
INPUT DATA SET CONTAINS COMPRESSED DATA
USING HUFFMAN COMPRESSION TYPE
INPUT DICTIONARY WAS BUILT BY INSERT
4,096 DICTIONARY SIZE USED
0 FREEPAGE VALUE USED
5 PCTFREE VALUE USED
COMPTYPE(ALL) REQUESTED
NO ROWLIMIT WAS REQUESTED
ESTIMATE BASED ON DB2 LOAD METHOD
255 MAXROWS VALUE USED
DSN1940I DSN1COMP COMPRESSION REPORT
HARDWARE SUPPORT FOR HUFFMAN COMPRESSION IS AVAILABLE
+-----------------------------------+------------------+------------------+------------------+------------------+
| | | Estimated state | Estimated state | Calculated |
| | UNCOMPRESSED | Compressed | Compressed | Compressed from |
| | | FIXED | HUFFMAN | INPUT DICTIONARY |
+-----------------------------------+------------------+------------------+------------------+------------------+
| DATA (IN KB) | 1,659,179 | 434,603 | 222,697 | 436,780 |
| PERCENT SAVINGS | | 73%| 86%| 73%|
| | | | | |
| AVERAGE BYTES PER ROW | 1,701 | 448 | 231 | 450 |
| PERCENT SAVINGS | | 73%| 86%| 73%|
| | | | | |
| DATA PAGES NEEDED | 500,000 | 125,000 | 62,500 | 125,000 |
| PERCENT DATA PAGES SAVED | | 75%| 87%| 75%|
| | | | | |
| DICTIONARY PAGES REQUIRED | 0 | 64 | 64 | 64 |
| ROWS SCANNED TO BUILD DICTIONARY | | 81 | 81 | N/A |
| ROWS SCANNED TO PROVIDE ESTIMATE | | 1,000,000 | 1,000,000 | N/A |
| DICTIONARY ENTRIES | | 4,096 | 4,080 | 4,096 |
| | | | | |
| TOTAL PAGES (DICTIONARY + DATA) | 500,000 | 125,064 | 62,564 | 125,064 |
| PERCENT SAVINGS | | 74%| 87%| 74%|
+-----------------------------------+------------------+------------------+------------------+------------------+
DSN1994I DSN1COMP COMPLETED SUCCESSFULLY, 118,475 PAGES PROCESSED The following example shows the DSN1COMP output for uncompressed data:
DSN1999I START OF DSN1COMP FOR JOB DSN1CMP COMPTS1
DSN1998I INPUT DSNAME = DSNC000.DSNDBC.EMPDB.EMPSPACE.I0001.A001 , VSAM
DSN1944I DSN1COMP INPUT PARAMETERS
INPUT DATA SET CONTAINS NON-COMPRESSED DATA
4,096 DICTIONARY SIZE USED
30 FREEPAGE VALUE USED
45 PCTFREE VALUE USED
COMPTYPE(FIXED) REQUESTED
NO ROWLIMIT WAS REQUESTED
ESTIMATE BASED ON DB2 REORG METHOD
255 MAXROWS VALUE USED
DSN1940I DSN1COMP COMPRESSION REPORT
HARDWARE SUPPORT FOR HUFFMAN COMPRESSION IS NOT AVAILABLE
+-----------------------------------+------------------+------------------+
| | | Estimated state |
| | UNCOMPRESSED | Compressed |
| | | FIXED |
+-----------------------------------+------------------+------------------+
| DATA (IN KB) | 224 | 142 |
| PERCENT SAVINGS | | 36%|
| | | |
| AVERAGE BYTES PER ROW | 48 | 32 |
| PERCENT SAVINGS | | 33%|
| | | |
| DATA PAGES NEEDED | 145 | 113 |
| PERCENT DATA PAGES SAVED | | 22%|
| | | |
| DICTIONARY PAGES REQUIRED | 0 | 16 |
| ROWS SCANNED TO BUILD DICTIONARY | | 1,969 |
| ROWS SCANNED TO PROVIDE ESTIMATE | | 5,000 |
| DICTIONARY ENTRIES | | 4,096 |
| | | |
| TOTAL PAGES (DICTIONARY + DATA) | 145 | 129 |
| PERCENT SAVINGS | | 11%|
+-----------------------------------+------------------+------------------+
DSN1994I DSN1COMP COMPLETED SUCCESSFULLY, 63 PAGES PROCESSED