59 lines
1.8 KiB
Markdown
59 lines
1.8 KiB
Markdown
# Table file structure
|
|
|
|
## Table file version changelog
|
|
|
|
### v0.1
|
|
Initial version.
|
|
|
|
## Overall specification
|
|
|
|
1. `TBL!` file signature (4 bytes)
|
|
2. Table file version (2 bytes)
|
|
3. The offset to the first page in a table. (8 bytes)
|
|
4. The offset to the last page in a table. (8 bytes)
|
|
5. The offset to the last available *free* page (8 bytes)
|
|
6. Pages (64 KiB each)
|
|
1. Page flags (1 byte)
|
|
2. Next page offset (8 bytes) **could be 0 if last page**
|
|
3. Row count (2 bytes)
|
|
4. Rows
|
|
1. Row flags (1 byte)
|
|
2. Row data
|
|
|
|
## Table file version specification
|
|
|
|
In the further time, it's planned to rewrite the file structure, so it's useful to have a version marker.
|
|
|
|
| 7-4 | 3-0 |
|
|
|---------------|---------------|
|
|
| Major version | Minor version |
|
|
|
|
That means that the first byte defines major version, and the second one defines minor version.
|
|
|
|
If tables with different versions are binary-compatible with each other, their major version must be the same.
|
|
|
|
## Page flags specification
|
|
|
|
| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
|
|
|-----|-----|-----|-----|-----|-----|-----|-----|
|
|
| RSV | RSV | RSV | RSV | RSV | RSV | RSV | DEL |
|
|
|
|
- **RSV** -- reserved for further usage.
|
|
- **DEL** -- free page flag.
|
|
|
|
## Row flags specification
|
|
|
|
See "Page flags specification" above.
|
|
|
|
## Free pages
|
|
|
|
A page can be called *free* iff all its rows are deleted.
|
|
If there is a free page, there actions are being done:
|
|
|
|
1. Set `DEL` page flag ((6.3) |= FLAG_DEL)
|
|
2. If a page is **not** the last one, replace next page offset in the previous page with a value in current page
|
|
((previous 6.1) = (6.1))
|
|
3. Put last available free page as the next page ((6.1) = 5)
|
|
4. Set current page offset as the offset to the last available free page ((5) = current_page_offset)
|
|
|