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Fabian Schmidt 2024-08-07 15:12:18 +02:00
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@ -14,10 +14,36 @@ Maybe having a file per table instead of per database is easier to set up, but i
### Format
| Offset | Description |
|---------|-------------|
| 0 | Something |
| todo!() | todo!() |
#### Header
| Offset | Length | Description | Example |
|---------|---------|-----------------------------------|----------------------------------------------------|
| 0 | 16 | Engine Version | MyDB-0.0.1 |
| 16 | 14 | Db Version | YYYYMMDDhhmmss |
| 30 | 64 | Table of Tables offset | Default: 512 |
| 94 | 64 | Table of Users offset | |
| 158 | 64 | Table of user to table | |
| 222 | 1 | Page Size as power of 2 | Default: 14 == 16,384 bytes<br>max 2<sup>255</sup> |
| 223 | 289 | Nothing | |
| 512 | 16284 | Default offset of table of tables | |
The table of tables contains the names and offsets in the file of all tables, or rather the first page of all tables.
Each table name can have a length of 32 bytes, the offset is a 64 byte integer and there is a 32 byte id so each row in this table is 128 bytes long.
The table of users contain the username and encrypted password of a user. Each username and password can have a max length of 32 and 60 bytes and there is a 32 byte id so 124 bytes per row.
The user to table table contains the read and write access of each user for each table. It uses the table of tables id, the table of users id and a byte for read access and a byte for write access. So 66 bytes per row.
Each table takes up at least one default page worth of space. Default page means that page sizes can vary depending on the table. A table with columns using up a ton of space might need more space per row than the default page size, there it wouldn't make much sense (I think) to have a static page size
#### Page
| Offset | Length | Description | Example |
| (from page offset) | | | |
|--------------------|--------|---------------------------------------|----------------------------------------------------|
| 0 | 64 | Number of pages | Default: 1 |
| 64 | 1024 | max 32 columns * 32 bytes per name | |
| 1088 | 64 | 1 byte per column to set as indexed | |
## SQL Interpreter