Is ANALYZE.FILE meant to give different averages for the same items in different spec'd Dynamic Files?

I had an expectation that record size averages would not change regardless of the setup of the dynamic file. I was wrong, aparently.

This is my initial test file

>ANALYZE.FILE TEST_DYN STATS NO.PAGE
File name                               = TEST_DYN
File has 301 groups (each * represents 10 groups analyzed).
******************************File name ..................   TEST_DYN
Pathname ...................   TEST_DYN
File type ..................   DYNAMIC
File style and revision ....   64BIT Revision 12
NLS Character Set Mapping ..   NONE
Hashing Algorithm ..........   GENERAL
No. of groups (modulus) ....   301 current ( minimum 1, 0 empty,
                                            300 overflowed, 300 badly )
Number of records ..........   2455
Large record size ..........   1619 bytes
Number of large records ....   1951
Group size .................   2048 bytes
Load factors ...............   80% (split), 50% (merge) and 80% (actual)
Total size .................   88696832 bytes
Total size of record data ..   88260487 bytes
Total size of record IDs ...   79401 bytes
Unused space ...............   352848 bytes
Total space for records ....   88692736 bytes

File name ..................   TEST_DYN
                               Number per group ( total of 301 groups )
                               Average    Minimum    Maximum     StdDev
Group buffers ..............    143.88          1        482      93.56
Records ....................      8.16          1         18       3.46
Large records ..............      6.48          1         15       3.01
Data bytes .................   3224.21       1325     985231    1552.70
Record ID bytes ............    263.79         36        589     112.10
Unused bytes ...............   1172.25         56       3028     606.56
Total bytes ................   4660.25       2048     987136       0.00

                               Number per record ( total of 2455 records )
                               Average    Minimum    Maximum     StdDev
Data bytes .................   5951.32         38     518138    0649.61
Record ID bytes ............     32.34          2         62       7.32
Total bytes ................   5983.66         40     518200    0650.80

File name ..................   TEST_DYN
                         Histogram of record and ID lengths

                                                                          60.7%
    Bytes ---------------------------------------------------------------------

  up to 4|
  up to 8|
 up to 16|
 up to 32|
 up to 64|
up to 128|
up to 256|
up to 512| >>>>>>>>>
 up to 1K| >>>>>>>
 up to 2K| >>>>>
 up to 4K| >>
 up to 8K| >>>>>
up to 16K| >>>>>>>>>>>>
     More| >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
          ---------------------------------------------------------------------
>

I wanted to test the impact of a different GROUP.SIZE setting, thinking it would/should influence the oversize group results.

It did, but making them larger not smaller.

The other strange result was a change in the average record size - what's with that!

>ICREATE.FILE DATA TEST_DYN$_301023 DYNAMIC GENERAL GROUP.SIZE 2 MINIMUM.MODULUS 2456
Creating file "TEST_DYN$_301023" as Type 30.
>

>COPYI FROM TEST_DYN TO TEST_DYN$_301023 ALL OVERWRITING

2455 records copied.
>ANALYZE.FILE TEST_DYN$_301023 STATS NO.PAGE
File name                               = TEST_DYN$_301023
File has 2456 groups (each * represents 10 groups analyzed).
********************************************************************************
********************************************************************************
********************************************************************************
*****File name ..................   TEST_DYN$_301023
Pathname ...................   TEST_DYN$_301023
File type ..................   DYNAMIC
File style and revision ....   64BIT Revision 12
NLS Character Set Mapping ..   NONE
Hashing Algorithm ..........   GENERAL
No. of groups (modulus) ....   2456 current ( minimum 2456, 934 empty,
                                            1285 overflowed, 1263 badly )
Number of records ..........   2455
Large record size ..........   3257 bytes
Number of large records ....   1867
Group size .................   4096 bytes
Load factors ...............   80% (split), 50% (merge) and 6% (actual)
Total size .................   99160064 bytes
Total size of record data ..   89682841 bytes
Total size of record IDs ...   78591 bytes
Unused space ...............   9390440 bytes
Total space for records ....   99151872 bytes

File name ..................   TEST_DYN$_301023
                               Number per group ( total of 2456 groups )
                               Average    Minimum    Maximum     StdDev
Group buffers ..............      9.86          1        148      15.37
Records ....................      1.00          1          5       1.02
Large records ..............      0.76          1          5       0.89
Data bytes .................   6515.81         27     602257    2967.32
Record ID bytes ............     32.00          2        175      33.24
Unused bytes ...............   3823.47         88       4096     558.45
Total bytes ................   0371.28       4096     606208       0.00

                               Number per record ( total of 2455 records )
                               Average    Minimum    Maximum     StdDev
Data bytes .................   6530.69         38     516090    0615.47
Record ID bytes ............     32.01          2         62       7.40
Total bytes ................   6562.70         40     516152    0616.95

File name ..................   TEST_DYN$_301023
                         Histogram of record and ID lengths

                                                                          63.8%
    Bytes ---------------------------------------------------------------------

  up to 4|
  up to 8|
 up to 16|
 up to 32|
 up to 64|
up to 128|
up to 256|
up to 512| >>>>>>>>>
 up to 1K| >>>>>>
 up to 2K| >>>>>>>
 up to 4K| >
 up to 8K| >
up to 16K| >>>>>>>>>>>
     More| >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
          ---------------------------------------------------------------------
>

Hi Gregor,

It looks like the average data bytes per record does include some overhead associated with each record/group. It looks to be calculated by dividing the "Total size of record data" by the number of records. The first file has that calculation set at 88260487 bytes and the second file has that set at 89682841. Given the same number of records, I'm guessing that changing the minimum modulus to 2456 from 301 in addition to changing the group size was a factor. Although this is just a guess at this point. I would be interested to see the results if you change the minimum modulus back to 301 on the TEST_DYN$_301023 file to see how that impacts the results? 

On a related note, the averages appear to be restricted to 4 digits and the leading digit appears truncated. I was initially confused as multiplying the average by the number of records was not matching up with the total.

Thanks,

Neil

Interesting feedback @Neil Morris

It seems to me that  both the number truncation and the average size calculation are bugs, unless they are both "by design".

Hi Gregor,

It looks like the average data bytes per record does include some overhead associated with each record/group. It looks to be calculated by dividing the "Total size of record data" by the number of records. The first file has that calculation set at 88260487 bytes and the second file has that set at 89682841. Given the same number of records, I'm guessing that changing the minimum modulus to 2456 from 301 in addition to changing the group size was a factor. Although this is just a guess at this point. I would be interested to see the results if you change the minimum modulus back to 301 on the TEST_DYN$_301023 file to see how that impacts the results? 

On a related note, the averages appear to be restricted to 4 digits and the leading digit appears truncated. I was initially confused as multiplying the average by the number of records was not matching up with the total.

Thanks,

Neil

FYI

I have raised a support case (#00929012) to look at the truncation of output in ANALYZE.FILE.