Enum MemoryStrategy 

#[non_exhaustive]
pub enum MemoryStrategy {
    Bounded,
    Auto,
    Mirrored,
}

How much memory a read-write open may use to hold the file being edited.

The two read-write backends differ in memory, not in what they can express: a bounded session reads through a handle and holds only what a commit is building, while a mirrored session materializes the whole file in memory. Bounded is the better default when it applies, but it cannot yet edit every file — a pre-v2 (non-latest-format) superblock or a userblock still needs the mirror.

This is what a caller says about that trade-off, on FileAccessProperties::with_memory_strategy. Leaving it unset lets the entry point decide: File::open_rw prefers the bounded engine and falls back to the mirror (Auto). Stating Bounded refuses instead of falling back.

This is a request, so it is deliberately not the type a file answers with: File::edit_backing returns an EditBacking, which cannot express Auto.

Sealed: unlike FileLocking or FileSpaceStrategy, whose variant sets mirror a closed C-library enum, this is a policy this crate invented, so a fourth strategy must not be a breaking change.

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

Bounded

Never build a whole-file mirror. A file the bounded engine cannot edit is refused at open with Error::EditUnsupported, before anything is staged.

Auto

Prefer the bounded engine, but fall back to the whole-file mirror for a file it cannot edit, rather than refusing. Memory then scales with the file, which is the cost of the file opening at all. What File::open_rw uses when nothing is asked for.

Two files reach that fallback, and no others: one with a pre-v2 (non-latest-format) superblock, and one with a userblock (a non-zero base address). Every other file a read-write open accepts is edited bounded, whatever its FileSpaceStrategy, whether or not it persists its free space, and however large it is. A paged file with no persisted free space is refused by both backings rather than mirrored, so it is not a third case. The list being exhaustive is what makes “prefer bounded” a guarantee to budget against: wherever Bounded opens a file, Auto gives the same backing.

Mirrored

Always build the whole-file mirror, whatever the file looks like. What File::open_rw did before it learned to dispatch.

Trait Implementations

impl Clone for MemoryStrategy

fn clone(&self) -> MemoryStrategy

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for MemoryStrategy

impl Debug for MemoryStrategy

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Eq for MemoryStrategy

impl From<EditBacking> for MemoryStrategy

fn from(backing: EditBacking) -> Self

Turns an outcome back into the request that pins it, so a caller can reopen a file onto the backing it got the first time: with_memory_strategy(file.edit_backing().unwrap().into()).

impl PartialEq for MemoryStrategy

fn eq(&self, other: &MemoryStrategy) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for MemoryStrategy