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use super::*;
/// A user of a `PageCache` needs to provide a `Materializer` which
/// handles the merging of page fragments.
pub trait Materializer {
/// The possibly fragmented page, written to log storage sequentially, and
/// read in parallel from multiple locations on disk when serving
/// a request to read the page. These will be merged to a single version
/// at read time, and possibly cached.
type PageFrag;
#[doc(hidden)]
fn is_null() -> bool
where
Self: Sized,
{
false
}
/// Used to merge chains of partial pages into a form
/// that is useful for the `PageCache` owner.
fn merge<'a, I>(frags: I, config: &Config) -> Self::PageFrag
where
I: IntoIterator<Item = &'a Self::PageFrag>,
Self::PageFrag: 'a;
/// Used to determine the size of the value for caching purposes.
fn size_in_bytes(frag: &Self::PageFrag) -> u64;
}
/// A materializer for things that have nothing to
/// materialize or recover, like a standalone `Log`.
#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
pub struct NullMaterializer;
impl Materializer for NullMaterializer {
type PageFrag = ();
#[doc(hidden)]
fn is_null() -> bool {
true
}
fn merge<'a, I>(_frags: I, _config: &Config) -> Self::PageFrag
where
I: IntoIterator<Item = &'a Self::PageFrag>,
{
}
fn size_in_bytes(_: &Self::PageFrag) -> u64 {
0
}
}