kmwebnet/OpenSK
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Introduce window size to fix hidden entries

Browse Source
This commit is contained in:
Julien Cretin
2021-10-01 17:50:49 +02:00
committed by Julien Cretin
parent 9dc5286633
commit af3bee64a5
3 changed files with 96 additions and 65 deletions
Download Patch File Download Diff File Expand all files Collapse all files

27
libraries/persistent_store/src/format.rs
View File

@@ -264,14 +264,23 @@ impl Format {
self.bytes_to_words(self.max_value_len())
}
/// The virtual window size in words, denoted by W.
///
/// This is the span of virtual storage that is accessible. In particular, all store content
/// fits within this window.
///
/// We have W = (N - 1) × Q - M.
pub fn window_size(&self) -> Nat {
(self.num_pages() - 1) * self.virt_page_size() - self.max_prefix_len()
}
/// The total virtual capacity in words, denoted by V.
///
/// We have V = (N - 1) × (Q - 1) - M.
/// This is the span of virtual storage after which we trigger a compaction. This is smaller
/// than the virtual window because compaction may transiently overflow out of this virtual
/// capacity.
///
/// We can show V ≥ (N - 2) × (Q - 1) with the following steps:
/// - M ≤ Q - 1 from M < Q from [M](Format::max_prefix_len)'s definition
/// - -M ≥ -(Q - 1) from above
/// - V ≥ (N - 1) × (Q - 1) - (Q - 1) from V's definition
/// We have V = W - (N - 1) = (N - 1) × (Q - 1) - M.
pub fn virt_size(&self) -> Nat {
(self.num_pages() - 1) * (self.virt_page_size() - 1) - self.max_prefix_len()
}
@@ -281,9 +290,9 @@ impl Format {
/// We have C = V - N = (N - 1) × (Q - 2) - M - 1.
///
/// We can show C ≥ (N - 2) × (Q - 2) - 2 with the following steps:
/// - V ≥ (N - 2) × (Q - 1) from [V](Format::virt_size)'s definition
/// - C ≥ (N - 2) × (Q - 1) - N from C's definition
/// - (N - 2) × (Q - 1) - N = (N - 2) × (Q - 2) - 2 by calculus
/// - M ≤ Q - 1 from M < Q from [M](Format::max_prefix_len)'s definition
/// - C ≥ (N - 1) × (Q - 2) - (Q - 1) - 1 from C's definition
/// - C ≥ (N - 2) × (Q - 2) - 2 by calculus
pub fn total_capacity(&self) -> Nat {
// From the virtual capacity, we reserve N - 1 words for `Erase` entries and 1 word for a
// `Clear` entry.
@@ -353,7 +362,7 @@ impl Format {
WordState::Partial
} else {
let tail = COMPACT_TAIL.get(word);
if tail > self.virt_size() + self.max_prefix_len() {
if tail > self.window_size() {
return Err(StoreError::InvalidStorage);
}
WordState::Valid(CompactInfo { tail })