MyDB

I have no clue how databases work It has been so long since my DB course, all I know is that they use B-Trees to store data I'm gonna attempt to write my own DB anyway

File format

Train of thought

As far as I'm concerned, the most important thing is probably the way the database gets stored. I don't want it to be in memory so I will have to create a file (or more) on the filesystem in which all the data is going to be stored. As far as I know, sqlite stores databases in a single file, I'm not sure about others like postgresql, mysql/mariadb, oracledb, etc. Maybe having a file per table instead of per database is easier to set up, but it might be just as hard, and doing IO on multiple files might be bad for performance.

Format

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 max 2255
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

todo!()