The CA-Clipper index file is a modified B+ tree. The size of a page
is 1024 bytes. The first page is the header:
_______________________ _______
00h / 0 | Signature byte *9| ^
00h / 1 | (binary) *12| |
|-----------------------| |
00h / 2 | Indexing version no. | |
00h / 3 | (Compiler version) | |
|-----------------------| |
00h / 4 | Offset in file for | File
00h / 5 | first index page. | header
00h / 6 | (root) | |
00h / 7 | | (page 0)
|-----------------------| |
00h / 8 | Offset to an unused | |
00h / 9 | next key page. *11| |
00h / 10 | | |
00h / 11 | | |
|-----------------------| |
00h / 12 | Key size + 8 bytes *1| |
00h / 13 | | |
|-----------------------| |
00h / 14 | Key size | |
00h / 15 | | |
|-----------------------| |
00h / 16 | No. of decimals in | |
00h / 17 | key | |
|-----------------------| |
00h / 18 | Max. item *6| |
00h / 19 | | |
|-----------------------| |
00h / 20 | Half page *7| |
00h / 21 | | |
|-----------------------| |
00h / 22 | Key expression. *8| |
00h / 23 | (NULL terminated) | |
: : |
00h / 277 | | |
|-----------------------| |
00h / 278 | Unique index flag *3| |
|-----------------------| |
00h / 279 | (Unused) | |
: : |
: : |
00h / 1023| | |
1 x 1024 |=======================| _v_____
00h / 0| Address of next empty | ^
00h / 1| page *11| |
00h / 2| | |
00h / 3| | |
|-----------------------| Empty page
: (Reserved) | (in linked list)
: | |
: | |
00h / 1023: | |
2 x 1024 |=======================| ___V___
| No. of used entries | |
| on current page (N) | |
|-----------------------| Used
| Array of N unsigned | page
: longs *5: |
: : |
|-----------------------| |
| Array of index | |
: entries : |
: : | __ |=======================|
: : | / 0| Address of left page |
| | | / 1| in tree *4|
| | | / 2| |
| | | / 3| |
|=======================| ___|____/ |-----------------------|
| Array of index | | 4| Record no. in DBF |
: : | 5| |
: : | 6| |
: : | 7| |
: : | |-----------------------|
: : | 8| Key field |
: : ___|____ : :
|=======================| | \ N| |
| | | \_____ |=======================|
: : |
|__End_of_File__________| ___v____ End of file ( 1Ah )
See NDX example
- Also called signature.
Distance between key pages. size + 2 longs. ie.e Left pointer + record no.
- The first, or root page
of an indes has a minimum of 1 entry regardless of this value.
- Unique index flag
- Address of left page in tree
This number will be between the minimum (half page) and maximum (max. item)
defined in the header unless it is the root page.
- Array on unsigned longs
The array length is equal to the maximum number of key entries per page
+1. Value 00h = No record. Other values: Record offset from start of page
- Max. item
.
The maximum number of keys (with their pointers) that can fit on an index
page.
- Half page
.
The maximum number of keys that can fit on an index page, divided by two.
This is an important value in a B-tree system as it is the minimum number
of keys that must be on a page.
- Key expression
The actual expression on which the index was built. It is a NULL terminated
string with at max length of 256 bytes.
- Version no
| 0003h |
Clipper 87 |
| 0006h |
Clipper 5.x |
- ??
This is a reference to the first page in a linked list of empty pages in
beteen valid data.
- Offset of next unused pages
Address 00 00 00 00h is the last empty page in chain.
- Binary version no
Stored as:
|
Value
|
Description
|
|
03h 00h
|
Default
|
|
00h 03h
|
Clipper 87
|
|
00h 06h
|
Clipper 5.x
|