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fill out some details about the database definition page (page 0) and the text

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code page/sort order info.
This commit is contained in:
James Ahlborn
2011-04-05 23:27:30 -04:00
parent fd1b777634
commit bbb73a0a83
1 changed files with 22 additions and 12 deletions
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34
HACKING
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@@ -73,19 +73,29 @@ The first byte of each page identifies the page type as follows.
Database Definition Page
------------------------
Each MDB database has a single definition page located at beginning of the file.
Not a lot is known about this page, and it is one of the least documented page
types. However, it contains things like Jet version, encryption keys, and name
of the creating program.
Each MDB database has a single definition page located at beginning of the
file. Not a lot is known about this page, and it is one of the least
documented page types. However, it contains things like Jet version,
encryption keys, and name of the creating program. Note, this page is
"encrypted" with a simple rc4 key starting at offset 0x18 and extending for
126 (Jet3) or 128 (Jet4) bytes.
Offset 0x14 contains the Jet version of this database: 0x00 for 3, 0x01 for 4,
0x02 for 5, 0x03 for Access 2010.
This is used by the mdb-ver utility to determine the Jet version.
The 14 bytes starting at 0x42 are the (encrypted) database password.
The 20 bytes (Jet3) or 40 bytes (Jet4) starting at 0x42 are the database
password. In Jet4, there is an additional mask applied to this password
derived from the database creation date (also stored on this page as 8 bytes
starting at offset 0x72).
The 4 bytes at 0x3e on the Database Definition Page are the database key.
The 2 bytes at 0x3C are the default database code page (useless in Jet4?).
The 2 bytes at 0x3A (Jet3) or 4 bytes at 0x6E (Jet4) are the default text
collating sort order.
Data Pages
----------
@@ -314,9 +324,9 @@ next_pg field.
| ???? | 2 bytes | col_num | Column Number (includes deleted columns) |
| ???? | 2 bytes | offset_V | Offset for variable length columns |
| ???? | 2 bytes | col_num | Column Number |
| ???? | 2 bytes | ??? | |
| ???? | 1 byte | precision | precision if numeric column |
| ???? | 1 byte | scale | scale if numeric column |
| ???? | 2 bytes | sort_order | textual column sort order(0x409=General) |
| ???? | 2 bytes | misc | prec/scale (1 byte each), or code page |
| | | | for textual columns (0x4E4=cp1252) |
| ???? | 2 bytes | ??? | |
| ???? | 1 byte | bitmask | See Column flags bellow |
| ???? | 2 bytes | offset_F | Offset for fixed length columns |
@@ -402,7 +412,7 @@ next_pg field.
| ???? | 2 bytes | col_num | Column Number |
| ???? | 2 bytes | misc | prec/scale (1 byte each), or sort order |
| | | | for textual columns(0x409=General) |
| ???? | 2 bytes | ??? | |
| ???? | 2 bytes | misc_ext | text sort order version num is 2nd byte |
| ???? | 1 byte | bitmask | See column flags below |
| ???? | 1 byte | misc_flags | 0x01 for compressed unicode |
| 0000 | 4 bytes | ??? | |
@@ -721,9 +731,9 @@ Once converted into this (non-ascii) character set, the text value can be
sorted in 'alphabetic' order using the lexicographical order of the entry
bytes. A text column will end with a NULL (0x00 or 0xff if negated).
Note, this encoding is the "General" sort order in Access 2000-2007. As of
Access 2010, this is now called the "General legacy" sort order, and the 2010
"General" sort order is a new encoding.
Note, this encoding is the "General" sort order in Access 2000-2007 (1033,
version 0). As of Access 2010, this is now called the "General legacy" sort
order, and the 2010 "General" sort order is a new encoding (1033, vesion 1).
The leaf page entries store the key column and the 3 byte page and 1 byte row
number.