DSN1COMP output
The DSN1COMP utility generates a report that includes the estimated space savings that can be achieved by using compression.
The first part of the report lists the input parameters in message DSN1944I. For table spaces, this message also reports whether the input data set was compressed and if so, the type of compression used. For example:
INPUT DATA SET CONTAINS COMPRESSED DATA
USING HUFFMAN COMPRESSION TYPE
If a compression dictionary exists, this message also reports whether the existing dictionary was
built by an insert operation or by a utility. For
example:
INPUT DICTIONARY WAS BUILT BY INSERTMessage DSN1940I then lists the requested compression estimates. For table spaces, this message also reports whether the hardware required for Huffman compression (IBM z14® or later) is available.
For table space reports, the following fields contain the indicated values:
- DATA PAGES NEEDED
- The number of pages that are needed for data. For the columns that report compression information, this value is calculated based on the percent of savings from the estimated total uncompressed data.
- DICTIONARY PAGES REQUIRED
- The estimated number of pages required to build dictionary pages. For segmented (non-UTS) table spaces or universal table spaces (UTS), these pages are calculated based on the segment boundary. The entire segment is allocated for the dictionary pages and the SEGSIZE value contributes to the number of pages that are reserved for the dictionary pages. DICTIONARY PAGES REQUIRED does not reflect the actual number of pages used for the dictionary.
- TOTAL PAGES
- The total number of pages. For the columns that report compression information, this value is calculated based on the percent of savings from the estimated total uncompressed data.
Message DSN1994I reports the number of physical pages that are processed from the
input file.
Tip: If you receive message DSN1941I, use a data set with
more rows as input, or specify a larger value for ROWLIMIT.
Sample DSN1COMP reports for a table space
The following four sample reports show the DSN1COMP output for a table space based on the type of compression estimate (COMPTYPE) requested where the input data set is uncompressed.
COMPTYPE not specified: The following sample report shows the output when COMPTYPE is not specified. In this case, DSN1COMP was run on IBM z14 or later hardware. (If DSN1COMP is run on earlier hardware, the report omits the Huffman compression estimate.)
DSN1999I START OF DSN1COMP FOR JOB DSN1CMP COMPTS4
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
0 FREEPAGE VALUE USED
5 PCTFREE VALUE USED
COMPTYPE NOT SPECIFIED
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 |
| | UNCOMPRESSED | Compressed | Compressed |
| | | FIXED | HUFFMAN |
+-----------------------------------+------------------+------------------+------------------+
| DATA (IN KB) | 224 | 178 | 173 |
| PERCENT SAVINGS | | 20%| 22%|
| | | | |
| AVERAGE BYTES PER ROW | 48 | 39 | 38 |
| PERCENT SAVINGS | | 18%| 20%|
| | | | |
| DATA PAGES NEEDED | 63 | 68 | 70 |
| PERCENT DATA PAGES SAVED | | 7%| 11%|
| | | | |
| DICTIONARY PAGES REQUIRED | 0 | 16 | 20 |
| ROWS SCANNED TO BUILD DICTIONARY | | 1,969 | 1,969 |
| ROWS SCANNED TO PROVIDE ESTIMATE | | 5,000 | 5,000 |
| DICTIONARY ENTRIES | | 4,096 | 4,080 |
| | | | |
| TOTAL PAGES (DICTIONARY + DATA) | 63 | 84 | 90 |
| PERCENT SAVINGS | | 33%| 42%|
+-----------------------------------+------------------+------------------+------------------+
DSN1994I DSN1COMP COMPLETED SUCCESSFULLY, 63 PAGES PROCESSEDCOMPTYPE(ALL) The following sample report shows the output for a table space when COMPTYPE(ALL) is specified. It includes the estimated space savings for both fixed-length and Huffman compression.
DSN1999I START OF DSN1COMP FOR JOB DSN1CMP STEP2
DSN1998I INPUT DSNAME = DSNC000.DSNDBC.DB1.TS1.I0001.A001 , VSAM
DSN1944I DSN1COMP INPUT PARAMETERS
INPUT DATA SET CONTAINS NON-COMPRESSED DATA
4,096 DICTIONARY SIZE USED
0 FREEPAGE VALUE USED
5 PCTFREE VALUE USED
NO ROWLIMIT WAS REQUESTED
ESTIMATE BASED ON DB2 LOAD METHOD
255 MAXROWS VALUE USED
255 MAXROWS VALUE USED
DSN1940I DSN1COMP COMPRESSION REPORT
Hardware support for Huffman compression is available
+-----------------------------------+------------------+------------------+------------------+
| | | Estimated state | Estimated state |
| | UNCOMPRESSED | Compressed | Compressed |
| | | FIXED | HUFFMAN |
+-----------------------------------+------------------+------------------+------------------+
| Data (in KB) | 1,758 | 1,232 | 1,278 |
| Percent savings | | 29%| 27%|
| | | | |
| Average Bytes per row | 38 | 28 | 29 |
| Percent savings | | 26%| 23%|
| | | | |
| Data Pages needed | 496 | 381 | 398 |
| Percent Data pages saved | | 23%| 19%|
| | | | |
| Dictionary pages required | 0 | 16 | 19 |
| Rows scanned to build dictionary | | 5,311 | 5,311 |
| Rows scanned to provide estimate | | 50,000 | 50,000 |
| Dictionary Entries | | 4,096 | 4,080 |
| | | | |
| Total Pages (Dictionary + Data) | 496 | 397 | 417 |
| Percent savings | | 19%| 15%|
+-----------------------------------+------------------+------------------+------------------+
DSN1994I DSN1COMP COMPLETED SUCCESSFULLY, 475 PAGES PROCESSED
COMPTYPE(FIXED) The following sample report shows the output for a table space when COMPTYPE(FIXED) is specified. It includes the estimated space savings for only fixed-length compression.
DSN1999I START OF DSN1COMP FOR JOB DSN1CMP STEP2
DSN1998I INPUT DSNAME = DSNC000.DSNDBC.DB1.TS1.I0001.A001 , VSAM
DSN1944I DSN1COMP INPUT PARAMETERS
INPUT DATA SET CONTAINS NON-COMPRESSED DATA
4,096 DICTIONARY SIZE USED
0 FREEPAGE VALUE USED
5 PCTFREE VALUE USED
NO ROWLIMIT WAS REQUESTED
ESTIMATE BASED ON DB2 LOAD METHOD
255 MAXROWS VALUE USED
255 MAXROWS VALUE USED
DSN1940I DSN1COMP COMPRESSION REPORT
Hardware support for Huffman compression is available
+-----------------------------------+------------------+------------------+
| | | Estimated state |
| | UNCOMPRESSED | Compressed |
| | | FIXED |
+-----------------------------------+------------------+------------------+
| Data (in KB) | 1,758 | 1,232 |
| Percent savings | | 29%|
| | | |
| Average Bytes per row | 38 | 28 |
| Percent savings | | 26%|
| | | |
| Data Pages needed | 496 | 381 |
| Percent Data pages saved | | 23%|
| | | |
| Dictionary pages required | 0 | 16 |
| Rows scanned to build dictionary | | 5,311 |
| Rows scanned to provide estimate | | 50,000 |
| Dictionary Entries | | 4,096 |
| | | |
| Total Pages (Dictionary + Data) | 496 | 397 |
| Percent savings | | 19%|
+-----------------------------------+------------------+------------------+
DSN1994I DSN1COMP COMPLETED SUCCESSFULLY, 475 PAGES PROCESSEDCOMPTYPE(HUFFMAN) The following sample report shows the output for a table space when COMPTYPE(HUFFMAN) is specified. It includes the estimated space savings for only Huffman compression.
DSN1999I START OF DSN1COMP FOR JOB DSN1CMP STEP2
DSN1998I INPUT DSNAME = DSNC000.DSNDBC.DB1.TS1.I0001.A001 , VSAM
DSN1944I DSN1COMP INPUT PARAMETERS
INPUT DATA SET CONTAINS NON-COMPRESSED DATA
4,096 DICTIONARY SIZE USED
0 FREEPAGE VALUE USED
5 PCTFREE VALUE USED
NO ROWLIMIT WAS REQUESTED
ESTIMATE BASED ON DB2 LOAD METHOD
255 MAXROWS VALUE USED
255 MAXROWS VALUE USED
DSN1940I DSN1COMP COMPRESSION REPORT
Hardware support for Huffman compression is available
+-----------------------------------+------------------+------------------+
| | | Estimated state |
| | UNCOMPRESSED | Compressed |
| | | HUFFMAN |
+-----------------------------------+------------------+------------------+
| Data (in KB) | 1,758 | 1,278 |
| Percent savings | | 27%|
| | | |
| Average Bytes per row | 38 | 29 |
| Percent savings | | 23%|
| | | |
| Data Pages needed | 496 | 398 |
| Percent Data pages saved | | 19%|
| | | |
| Dictionary pages required | 0 | 19 |
| Rows scanned to build dictionary | | 5,311 |
| Rows scanned to provide estimate | | 50,000 |
| Dictionary Entries | | 4,080 |
| | | |
| Total Pages (Dictionary + Data) | 496 | 417 |
| Percent savings | | 15%|
+-----------------------------------+------------------+------------------+
DSN1994I DSN1COMP COMPLETED SUCCESSFULLY, 475 PAGES PROCESSEDCompressed input: The following sample report shows the output for a table space when the input data set is compressed. The output includes an extra column with information from the input compression dictionary.
DSN1999I START OF DSN1COMP FOR JOB DSN1CMP STEP2
DSN1998I INPUT DSNAME = DB2DUMP.DSNDBD.DBPBR2.TSPBR2.I0001.A001 , SEQ
DSN1944I DSN1COMP INPUT PARAMETERS
INPUT DATA SET CONTAINS COMPRESSED DATA
USING FIXED-LENGTH COMPRESSION TYPE
INPUT DICTIONARY WAS BUILT BY INSERT
4,096 DICTIONARYSIZE USED
0 FREEPAGE VALUE USED
5 PCTFREE VALUE USED
COMPTYPE NOT SPECIFIED
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 Sample DSN1COMP report for an index
When you run DSN1COMP on an index, the generated report includes the estimated reduction in leaf page space, as shown in the following sample report:
DSN1999I START OF DSN1COMP FOR JOB DSN1COMP STEP2
DSN1998I INPUT DSNAME = TESTCAT.DSNDBD.DB1COMPR.I1.I0001.A001 , VSAM
DSN1944I DSN1COMP INPUT PARAMETERS
PROCESSING PARMS FOR INDEX DATASET:
NO LEAFLIM WAS REQUESTED
DSN1940I DSN1COMP COMPRESSION REPORT
38 Index Leaf Pages Processed
3,000 Keys Processed
3,000 Rids Processed
401 KB of Key Data Processed
106 KB of Compressed Keys Produced
EVALUATION OF COMPRESSION WITH DIFFERENT INDEX PAGE SIZES:
----------------------------------------------
8 K Page Buffer Size yields a
51 % Reduction in Index Leaf Page Space
The Resulting Index would have approximately
49 % of the original index's Leaf Page Space
No Bufferpool Space would be unused
----------------------------------------------
----------------------------------------------
16 K Page Buffer Size yields a
74 % Reduction in Index Leaf Page Space
The Resulting Index would have approximately
26 % of the original index's Leaf Page Space
3 % of Bufferpool Space would be unused to
ensure keys fit into compressed buffers
----------------------------------------------
DSN1994I DSN1COMP COMPLETED SUCCESSFULLY, 38 PAGES PROCESSED
Sample DSN1COMP report for an uncompressed LOB table space
When you run DSN1COMP on an uncompressed LOB table space, the generated report includes the estimated data pages saved for each page size, as shown in the following sample report:
DSN1944I DSN1COMP INPUT PARAMETERS
PROCESSING PARMS FOR LOB DATASET:
LOB
DSN1940I DSN1COMP COMPRESSION REPORT
DSN1COMP run on uncompressed LOB table space
LOB table space statistics
---------------------------------------------------------
Number of LOBs 15 LOBs
Minimum LOB size 5 KB
Maximum LOB size 148 KB
Average LOB size 59 KB
LOB compression ratio
---------------------------------------------------------
Total LOB data compressed 656 KB
Total LOB data uncompressed 887 KB
Percentage of KB saved 27 %
Minimum System pages required 36 Pages
Data pages needed for compressed LOB table space 149 Pages
Data pages needed for uncompressed LOB table space 210 Pages
Percentage of Data pages saved 30 %
Current page size 4 KB
EVALUATION OF COMPRESSION WITH DIFFERENT PAGE SIZES
Note: System Pages may contain LOB data!
---------------------------------------------------------
4K page size:
Minimum System pages required 36 Pages
Additional Data pages needed for compressed LOBs 149 Pages
Additional Data pages needed for uncompressed LOBs 210 Pages
Data pages saved (not including system pages) 30 %
8K page size:
Minimum System pages required 36 Pages
Additional Data pages needed for compressed LOBs 81 Pages
Additional Data pages needed for uncompressed LOBs 102 Pages
Data pages saved (not including system pages) 21 %
16K page size:
Minimum System pages required 36 Pages
Additional Data pages needed for compressed LOBs 41 Pages
Additional Data pages needed for uncompressed LOBs 49 Pages
Data pages saved (not including system pages) 17 %
32K page size:
Minimum System pages required 36 Pages
Additional Data pages needed for compressed LOBs 20 Pages
Additional Data pages needed for uncompressed LOBs 20 Pages
Data pages saved (not including system pages) 0 %
DSN1994I DSN1COMP COMPLETED SUCCESSFULLY, 2,520 PAGES PROCESSED
Sample DSN1COMP report for a compressed LOB table space
When you run DSN1COMP on a compressed LOB table space, the generated report includes the estimated data pages saved for each page size, as shown in the following sample report:
DSN1944I DSN1COMP INPUT PARAMETERS
PROCESSING PARMS FOR LOB DATASET:
LOB
DSN1940I DSN1COMP COMPRESSION REPORT
DSN1COMP run on compressed LOB table space
LOB table space statistics
---------------------------------------------------------
Number of LOBs 15 LOBs
Minimum LOB size 5 KB
Maximum LOB size 148 KB
Average LOB size 28 KB
Table space with compression (in KB)
---------------------------------------------------------
Total uncompressed data 0 KB
Total compressed data 241 KB
Total LOB data 241 KB
Table space if uncompressed (in KB)
---------------------------------------------------------
Total uncompressed data 428 KB
Total compressed data 0 KB
Total LOB data 428 KB
LOB compression ratio
---------------------------------------------------------
Total LOB data compressed 241 KB
Total LOB data uncompressed 428 KB
Percentage of KB saved 44 %
Minimum System pages required 36 Pages
Data pages needed for compressed LOB table space 47 Pages
Data pages needed for uncompressed LOB table space 95 Pages
Percentage of Data pages saved 51 %
Current page size 4 KB
EVALUATION OF COMPRESSION WITH DIFFERENT PAGE SIZES
Note: System Pages may contain LOB data!
---------------------------------------------------------
4K page size:
Minimum System pages required 36 Pages
Additional Data pages needed for compressed LOBs 47 Pages
Additional Data pages needed for uncompressed LOBs 95 Pages
Data pages saved (not including system pages) 51 %
8K page size:
Minimum System pages required 36 Pages
Additional Data pages needed for compressed LOBs 23 Pages
Additional Data pages needed for uncompressed LOBs 45 Pages
Data pages saved (not including system pages) 49 %
16K page size:
Minimum System pages required 36 Pages
Additional Data pages needed for compressed LOBs 7 Pages
Additional Data pages needed for uncompressed LOBs 18 Pages
Data pages saved (not including system pages) 62 %
32K page size:
Minimum System pages required 36 Pages
Additional Data pages needed for compressed LOBs 3 Pages
Additional Data pages needed for uncompressed LOBs 4 Pages
Data pages saved (not including system pages) 25 %
DSN1994I DSN1COMP COMPLETED SUCCESSFULLY, 2,520 PAGES PROCESSED