Crate sanakirja_core[−][src]
This crate defines tools to implement datastructures that can live in main memory or on-disk, meaning that their natural habitat is memory-mapped files, but if that environment is threatened, they might seek refuge in lower-level environments.
One core building block of this library is the notion of virtual
memory pages, which are allocated and freed by an
externally-provided allocator (see how the sanakirja
crate does
this). The particular implementation used here is meant to allow a
transactional system with readers reading the structures
concurrently with one writer at a time.
At the moment, only B trees are implemented, as well as the following general traits:
LoadPage
is a trait used to get a pointer to a page. In the most basic version, this may just return a pointer to the file, offset by the requested offset. In more sophisticated versions, this can be used to encrypt and compress pages.AllocPage
allocates and frees pages, because as datastructures need to be persisted on disk, we can't rely on Rust's memory management to do it for us. Users of this crate don't have to worry about this though.
Moreover, two other traits can be used to store things on pages:
Storable
is a simple trait that all Sized + Ord
types
without references can readily implement (the direct_repr!
macro does that). For types containing references to pages
allocated in the database, the comparison function can be
customised. Moreover, these types must supply an iterator over
these references, in order for reference-counting to work properly
when the datastructures referencing these types are forked.
Dynamically-sized types, or types that need to be represented in a
dynamically-sized way, can use the UnsizedStorable
format.
Modules
btree | An implementation of B trees. The core operations on B trees
(lookup, iterate, put and del) are generic in the actual
implementation of nodes, via the |
Macros
direct_repr | A macro to implement |
Structs
CowPage | Representation of a mutable or shared page. This is an owned page
(like |
MutPage | An owned page on which we can write. This is just a wrapper around
|
Page | Representation of a borrowed, or immutable page, like a slice in Rust. |
Constants
PAGE_SIZE | There's a hard-coded assumption that pages have 4K bytes. This is true for normal memory pages on almost all platforms. |
Traits
AllocPage | Trait for allocating and freeing pages. |
LoadPage | Trait for loading a page. |
Storable | Types that can be stored on disk. This trait may be used in
conjunction with |
UnsizedStorable | Types that can be stored on disk. |