Struct rustdb::compact::CompactFile

pub struct CompactFile {
    pub stg: Box<dyn Storage>,
    // some fields omitted
}

CompactFile stores logical pages in smaller regions of backing storage.

Each logical page has a fixed size “starter page”.

A logical page that does not fit in the “starter page” has 1 or more “extension pages”.

Each extension page starts with it’s containing logical page number ( to allow extension pages to be relocated as required ).

When a new extension page is needed, it is allocated from the end of the file.

When an extension page is freed, the last extension page in the file is relocated to fill it.

If the starter page array needs to be enlarged, the first extension page is relocated to the end of the file.

File layout: file header | starter pages | extension pages.

Layout of starter page: 2 byte logical page size | array of 8 byte page numbers | user data | unused data.

Note: for a free logical page, a special value is stored after the page size, then a link to the next free logical page.

Layout of extension page: 8 byte logical page number | user data | unused data.

Fields

stg: Box<dyn Storage>

Underlying storage.

Implementations

impl CompactFile

pub fn new(stg: Box<dyn Storage>, sp_size: usize, ep_size: usize) -> Self

Construct a new CompactFile.

pub fn lp_size(&self, lpnum: u64) -> usize

Get the current size of the specified logical page.

pub fn set_page(&mut self, lpnum: u64, data: Data)

Set the contents of the page.

pub fn get_page(&self, lpnum: u64) -> Data

Get logical page contents.

pub fn alloc_page(&mut self) -> u64

Allocate logical page number. Pages are numbered 0,1,2…

pub fn free_page(&mut self, pnum: u64)

Free a logical page number.

pub fn is_new(&self) -> bool

Is this a new file?

pub fn rollback(&mut self)

Resets logical page allocation to last save.

pub fn save(&mut self)

Process the temporary sets of free pages and write the file header.

pub fn compress(
    sp_size: usize,
    ep_size: usize,
    size: usize,
    saving: usize
) -> bool

Check whether compressing a page is worthwhile.

pub fn get_info(&self) -> (HashSet<u64>, u64)

Get the set of free logical pages ( also verifies free chain is ok ).