mirror of
https://github.com/featurebasedb/featurebase.git
synced 2026-10-07 11:27:50 +00:00
110 lines
2.2 KiB
Markdown
110 lines
2.2 KiB
Markdown
Roaring B-tree Format
|
|
=====================
|
|
|
|
The RBF format represents a Roaring bitmap whose containers are stored in the
|
|
leafs of a b-tree. This allows the bitmap to be efficiently queried & updated.
|
|
|
|
|
|
## File Format
|
|
|
|
The RBF file is divided into equal 8KB pages. Each page after the meta page
|
|
is numbered incrementally from 1 to 1^31.
|
|
|
|
Pages can be one of the following types:
|
|
|
|
- Meta page: contains header information.
|
|
- Branch page: contains pointers to lower branch & leaf pages.
|
|
- Leaf page: contains array and RLE container data.
|
|
- Bitmap page: contains bitmap container data.
|
|
|
|
All integer values are little endian encoded.
|
|
|
|
|
|
## Page header
|
|
|
|
Every page type except the bitmap page contains the following header:
|
|
|
|
|
|
### Meta page
|
|
|
|
The meta page contains the following header:
|
|
|
|
[4] magic (\xFFRBF)
|
|
[4] flags
|
|
[4] page count
|
|
[8] wal ID
|
|
[4] root records pgno
|
|
[4] freelist pgno
|
|
|
|
|
|
### Root Records page
|
|
|
|
A list of all b-tree names & their respective root page numbers are stored in
|
|
root record pages. Once a bitmap root is created, it is never moved so the
|
|
root record pages only need to be rewritten when creating, renaming, or deleting
|
|
a b-tree. If records exceed the size of a page then they are overflowed to
|
|
additional pages.
|
|
|
|
[4] page number
|
|
[4] flags
|
|
[4] overflow pgno
|
|
[*] bitmap records
|
|
|
|
Each bitmap record is represented as:
|
|
|
|
[4] pgno
|
|
[2] name size
|
|
[*] name
|
|
|
|
All bitmap records are loaded into memory when the file is opened.
|
|
|
|
|
|
### Branch page
|
|
|
|
The branch page contains the following header:
|
|
|
|
[4] page number
|
|
[4] flags
|
|
[2] cell count
|
|
[*] cell index (2 * cell count)
|
|
[*] padding for 4-byte alignment
|
|
|
|
Each cell is formatted as:
|
|
|
|
[8] highbits
|
|
[4] flags
|
|
[4] page number
|
|
|
|
|
|
### Leaf page
|
|
|
|
The leaf page contains the following header:
|
|
|
|
[4] page number
|
|
[4] flags
|
|
[2] cell count
|
|
[*] cell index (2 * cell count)
|
|
|
|
|
|
The leaf page contains a series of cells with the header of:
|
|
|
|
[8] highbits
|
|
[4] flag
|
|
[4] child count
|
|
[*] array or RLE data
|
|
|
|
|
|
### Bitmap page
|
|
|
|
The data for the bitmap page takes up the entire 8KB.
|
|
|
|
|
|
## Proof of Concept Notes
|
|
|
|
The following are notes made that are temporary for the RBF format. This will
|
|
change as development progresses:
|
|
|
|
- Transaction support is deferred
|
|
- WAL support is deferred
|
|
|
|
|