System Parameters

Description

The 'XK' (or '>K') parameter can be used to enable the PxPlus enhanced VLR file format, which provides both smaller and faster VLR files (most noticeable when you have large data blocks and small keys), and to allow VLR files to grow >2GB.

Files updated while this parameter is enabled use a modified key tree structure that is able to pack more keys per file key block. This results in less key blocks and smaller key trees. This new algorithm has been shown to reduce disk space by as much as 30%, depending on the file structure and keys.

Note:
VLR files written while this parameter is active will not be compatible with earlier releases if the file ends up with >255 keys per block or becomes >2GB.

(The 'XK' system parameter was added in PxPlus v10.00 and is fundamentally the same as '>K'.)

Default

Off

See Also

'>K' Enhanced VLR File Format

Example

To give you an idea as to what this means, the following is an analysis program (filecheck):

     begin
     input "File to check: ",X$;
     if ctl<>0 \
          then end
     open (1,isz=-1)X$
     read record (1,siz=256,ind=0)H$
     B_SZ=(dec(H$(241,1))+1)*1024
!
! Process all segments
!
     for SEG=1 to 100
          print "Processing:",pth(1)
          B_ADR=512
!
          while 1
               read record (1,ind=B_ADR,siz=B_SZ,err=*break)B$
               TOT_BLK++
               if B$(1,1)=$FE$ \
                    then KEY_BLK++;
                            KEY_FREE+=B_SZ-len(stp(B$,1,$00$))
               if B$(1,1)=$80$ \
                    then DTA_FREE+=dec($00$+B$(7,2));
                            DTA_BLK++
               if B$(1,1)=$00$ \
                    then FRE_BLK++
               if B$(1,1)=$FC$ \
                    then INV_BLK++
               if B$(1,1)=$FB$ \
                    then DCT_BLK++
               B_ADR+=B_SZ
          wend
!
! Open next segment if present
!
          close (1)
          open (1,isz=-1,err=*break)X$+"."+str(SEG:"000")
     next
!
     print "Total Blks:",TOT_BLK:"##,###,##0"," (for",TOT_BLK*B_SZ+512," bytes)"
     print "Total Segs:",SEG:"##,###,##0"
     print "  Key Blks:",KEY_BLK:"##,###,##0"," (for",KEY_BLK*B_SZ," bytes of which",KEY_FREE," is unused)"
     print " Free Blks:",FRE_BLK:"##,###,##0"," (for",FRE_BLK*B_SZ," bytes)"
     print "  Inv Blks:",INV_BLK:"##,###,##0"," (for",INV_BLK*B_SZ," bytes)"
     print " DictBlks:",DCT_BLK:"##,###,##0"," (for",DCT_BLK*B_SZ," bytes)"
     print " Data Blks:",DTA_BLK:"##,###,##0"," (for",DTA_BLK*B_SZ," bytes of which",DTA_FREE," is unused)"
     end

And a program to load a test data file (fileload):

erase "tstdta",err=*next
keyed "tstdta",6,0,0,bsz=8
open purge (1)"tstdta"
for I=1 to 10000
     write (1,key=str(I:"000000"))"This is record ",I
next I

And the results:

set_param 'XK'=0
run "fileload
run "filecheck'
File to check: tstdta
Processing:c:\temp\tstdta
Total Blks:        99 (for 811520 bytes)
Total Segs:         1
Key Blks:          54 (for 442368 bytes of which 331450 is unused)
Free Blks:           0 (for 0 bytes)
Inv Blks:              1 (for 8192 bytes)
Dict Blks:            0 (for 0 bytes)
Data Blks:         44 (for 360448 bytes of which 41202 is unused)
set_param 'XK'
run "fileload
run "filecheck
File to check: tstdta
Processing:c:\temp\tstdta
Total Blks:        64 (for 524800 bytes)
Total Segs:         1
Key Blks:          19 (for 155648 bytes of which 45325 is unused)
Free Blks:           0 (for 0 bytes)
Inv Blks:              1 (for 8192 bytes)
Dict Blks:            0 (for 0 bytes)
Data Blks:         44 (for 360448 bytes of which 41202 is unused)

As you can see in this example, the file went from 99 blocks down to 64 blocks (a 33% saving in disk space). In addition, the number of key blocks dropped from 54 to 19 (a 65% saving). Not only does using this option reduce the file size, but also the changes improve execution time by reducing the number of levels in the key tree.

For instance, without the 'XK' option, a file with over 62,500 records must have a three (3) level key tree regardless of key/block size. With this new option, a file with a 10-character key size and an 8K block can support a file with well over 250,000 records with only a two (2) level key tree.

Files > 2GB

When this parameter is enabled (On), VLR files will be allowed to grow beyond the 2GB limit imposed on earlier (pre-version 10) releases. The actual maximum file size will be determined by the actual block size: