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turso/core/storage/page_cache.rs
Pekka Enberg 8337e86794 core: Use sequential consistency for atomics by default 
We use relaxed ordering in a lot of places where we really need to
ensure all CPUs see the write. Switch to sequential consistency, unless
acquire/release is explicitly used. If there are places that can be
optimized, we can switch to relaxed case-by-case, but have a comment
explaning *why* it is safe.
2025-09-18 13:38:13 +03:00

1750 lines
56 KiB
Rust
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use std::sync::atomic::Ordering;
use std::sync::Arc;
use tracing::trace;
use crate::turso_assert;
use super::pager::PageRef;
/// FIXME: https://github.com/tursodatabase/turso/issues/1661
const DEFAULT_PAGE_CACHE_SIZE_IN_PAGES_MAKE_ME_SMALLER_ONCE_WAL_SPILL_IS_IMPLEMENTED: usize =
100000;
#[derive(Debug, Copy, Eq, Hash, PartialEq, Clone)]
#[repr(transparent)]
pub struct PageCacheKey(usize);
const NULL: usize = usize::MAX;
const CLEAR: u8 = 0;
const REF_MAX: u8 = 3;
#[derive(Clone, Debug)]
struct PageCacheEntry {
/// Key identifying this page
key: PageCacheKey,
/// The cached page, None if this slot is free
page: Option<PageRef>,
/// Reference counter (SIEVE/GClock): starts at zero, bumped on access,
/// decremented during eviction, only pages at 0 are evicted.
ref_bit: u8,
/// Index of next entry in SIEVE queue (older/toward tail)
next: usize,
/// Index of previous entry in SIEVE queue (newer/toward head)
prev: usize,
}
impl Default for PageCacheEntry {
fn default() -> Self {
Self {
key: PageCacheKey(0),
page: None,
ref_bit: CLEAR,
next: NULL,
prev: NULL,
}
}
}
impl PageCacheEntry {
#[inline]
fn bump_ref(&mut self) {
self.ref_bit = std::cmp::min(self.ref_bit + 1, REF_MAX);
}
#[inline]
/// Returns the old value
fn decrement_ref(&mut self) -> u8 {
let old = self.ref_bit;
self.ref_bit = old.saturating_sub(1);
old
}
#[inline]
fn clear_ref(&mut self) {
self.ref_bit = CLEAR;
}
#[inline]
fn empty() -> Self {
Self::default()
}
#[inline]
fn reset_links(&mut self) {
self.next = NULL;
self.prev = NULL;
}
}
/// PageCache implements a variation of the SIEVE algorithm that maintains an intrusive linked list queue of
/// pages which keep a 'reference_bit' to determine how recently/frequently the page has been accessed.
/// The bit is set to `Clear` on initial insertion and then bumped on each access and decremented
/// during eviction scans.
///
/// The ring is circular. `clock_hand` points at the tail (LRU).
/// Sweep order follows next: tail (LRU) -> head (MRU) -> .. -> tail
/// New pages are inserted after the clock hand in the `next` direction,
/// which places them at head (MRU) (i.e. `tail.next` is the head).
pub struct PageCache {
/// Capacity in pages
capacity: usize,
/// Map of Key -> usize in entries array
map: PageHashMap,
clock_hand: usize,
/// Fixed-size vec holding page entries
entries: Vec<PageCacheEntry>,
/// Free list: Stack of available slot indices
freelist: Vec<usize>,
}
unsafe impl Send for PageCache {}
unsafe impl Sync for PageCache {}
struct PageHashMap {
buckets: Vec<Vec<HashMapNode>>,
capacity: usize,
size: usize,
}
#[derive(Debug, Clone, PartialEq, thiserror::Error)]
pub enum CacheError {
#[error("{0}")]
InternalError(String),
#[error("page {pgno} is locked")]
Locked { pgno: usize },
#[error("page {pgno} is dirty")]
Dirty { pgno: usize },
#[error("page {pgno} is pinned")]
Pinned { pgno: usize },
#[error("cache active refs")]
ActiveRefs,
#[error("Page cache is full")]
Full,
#[error("key already exists")]
KeyExists,
}
#[derive(Debug, PartialEq)]
pub enum CacheResizeResult {
Done,
PendingEvictions,
}
impl PageCacheKey {
pub fn new(pgno: usize) -> Self {
Self(pgno)
}
}
impl PageCache {
pub fn new(capacity: usize) -> Self {
assert!(capacity > 0);
let freelist = (0..capacity).rev().collect::<Vec<usize>>();
Self {
capacity,
map: PageHashMap::new(capacity),
clock_hand: NULL,
entries: vec![PageCacheEntry::empty(); capacity],
freelist,
}
}
#[inline]
fn link_after(&mut self, a: usize, b: usize) {
// insert `b` after `a` in a non-empty circular list
let an = self.entries[a].next;
self.entries[b].prev = a;
self.entries[b].next = an;
self.entries[an].prev = b;
self.entries[a].next = b;
}
#[inline]
fn link_new_node(&mut self, slot: usize) {
let hand = self.clock_hand;
if hand == NULL {
// first element → points to itself
self.entries[slot].prev = slot;
self.entries[slot].next = slot;
self.clock_hand = slot;
} else {
// insert after the hand (LRU)
self.link_after(hand, slot);
}
}
#[inline]
fn unlink(&mut self, slot: usize) {
let p = self.entries[slot].prev;
let n = self.entries[slot].next;
if p == slot && n == slot {
self.clock_hand = NULL;
} else {
self.entries[p].next = n;
self.entries[n].prev = p;
if self.clock_hand == slot {
// stay at LRU position, second-oldest becomes oldest
self.clock_hand = p;
}
}
self.entries[slot].reset_links();
}
#[inline]
fn forward_of(&self, i: usize) -> usize {
self.entries[i].next
}
pub fn contains_key(&self, key: &PageCacheKey) -> bool {
self.map.contains_key(key)
}
#[inline]
pub fn insert(&mut self, key: PageCacheKey, value: PageRef) -> Result<(), CacheError> {
self._insert(key, value, false)
}
#[inline]
pub fn upsert_page(&mut self, key: PageCacheKey, value: PageRef) -> Result<(), CacheError> {
self._insert(key, value, true)
}
pub fn _insert(
&mut self,
key: PageCacheKey,
value: PageRef,
update_in_place: bool,
) -> Result<(), CacheError> {
trace!("insert(key={:?})", key);
let slot = self.map.get(&key);
if let Some(slot) = slot {
let p = self.entries[slot]
.page
.as_ref()
.expect("slot must have a page");
if !p.is_loaded() && !p.is_locked() {
// evict, then continue with fresh insert
self._delete(key, true)?;
let slot_index = self.find_free_slot()?;
let entry = &mut self.entries[slot_index];
entry.key = key;
entry.page = Some(value);
entry.clear_ref();
self.map.insert(key, slot_index);
self.link_new_node(slot_index);
return Ok(());
}
let existing = &mut self.entries[slot];
existing.bump_ref();
if update_in_place {
existing.page = Some(value);
return Ok(());
} else {
turso_assert!(
Arc::ptr_eq(existing.page.as_ref().unwrap(), &value),
"Attempted to insert different page with same key: {key:?}"
);
return Err(CacheError::KeyExists);
}
}
// Key doesn't exist, proceed with new entry
self.make_room_for(1)?;
let slot_index = self.find_free_slot()?;
let entry = &mut self.entries[slot_index];
turso_assert!(entry.page.is_none(), "page must be None in free slot");
entry.key = key;
entry.page = Some(value);
// Sieve ref bit starts cleared, will be set on first access
entry.clear_ref();
self.map.insert(key, slot_index);
self.link_new_node(slot_index);
Ok(())
}
fn find_free_slot(&mut self) -> Result<usize, CacheError> {
let slot = self.freelist.pop().ok_or_else(|| {
CacheError::InternalError("No free slots available after make_room_for".into())
})?;
#[cfg(debug_assertions)]
{
turso_assert!(
self.entries[slot].page.is_none(),
"allocating non-free slot {}",
slot
);
}
turso_assert!(
self.entries[slot].next == NULL && self.entries[slot].prev == NULL,
"freelist slot {} has non-NULL links",
slot
);
Ok(slot)
}
fn _delete(&mut self, key: PageCacheKey, clean_page: bool) -> Result<(), CacheError> {
if !self.contains_key(&key) {
return Ok(());
}
let slot_idx = self
.map
.get(&key)
.ok_or_else(|| CacheError::InternalError("Key exists but not found in map".into()))?;
let entry = self.entries[slot_idx]
.page
.as_ref()
.expect("page in map was None")
.clone();
if entry.is_locked() {
return Err(CacheError::Locked {
pgno: entry.get().id,
});
}
if entry.is_dirty() {
return Err(CacheError::Dirty {
pgno: entry.get().id,
});
}
if entry.is_pinned() {
return Err(CacheError::Pinned {
pgno: entry.get().id,
});
}
if clean_page {
entry.clear_loaded();
let _ = entry.get().contents.take();
}
// unlink from circular list and advance hand if needed
self.unlink(slot_idx);
self.map.remove(&key);
let e = &mut self.entries[slot_idx];
e.page = None;
e.clear_ref();
e.reset_links();
self.freelist.push(slot_idx);
Ok(())
}
#[inline]
/// Deletes a page from the cache
pub fn delete(&mut self, key: PageCacheKey) -> Result<(), CacheError> {
trace!("cache_delete(key={:?})", key);
self._delete(key, true)
}
#[inline]
pub fn get(&mut self, key: &PageCacheKey) -> crate::Result<Option<PageRef>> {
let Some(slot) = self.map.get(key) else {
return Ok(None);
};
// Because we can abort a read_page completion, this means a page can be in the cache but be unloaded and unlocked.
// However, if we do not evict that page from the page cache, we will return an unloaded page later which will trigger
// assertions later on. This is worsened by the fact that page cache is not per `Statement`, so you can abort a completion
// in one Statement, and trigger some error in the next one if we don't evict the page here.
let entry = &mut self.entries[slot];
let page = entry
.page
.as_ref()
.expect("page in the map to exist")
.clone();
if !page.is_loaded() && !page.is_locked() {
self.delete(*key)?;
return Ok(None);
}
entry.bump_ref();
Ok(Some(page))
}
#[inline]
pub fn peek(&mut self, key: &PageCacheKey, touch: bool) -> Option<PageRef> {
let slot = self.map.get(key)?;
let entry = &mut self.entries[slot];
let page = entry.page.as_ref()?.clone();
if touch {
entry.bump_ref();
}
Some(page)
}
/// Resizes the cache to a new capacity
/// If shrinking, attempts to evict pages.
/// If growing, simply increases capacity.
pub fn resize(&mut self, new_cap: usize) -> CacheResizeResult {
if new_cap == self.capacity {
return CacheResizeResult::Done;
}
if new_cap < self.len() {
let need = self.len() - new_cap;
let mut evicted = 0;
while evicted < need {
match self.make_room_for(1) {
Ok(()) => evicted += 1,
Err(CacheError::Full) => return CacheResizeResult::PendingEvictions,
Err(_) => return CacheResizeResult::PendingEvictions,
}
}
}
assert!(new_cap > 0);
// Collect survivors starting from hand, one full cycle
struct Payload {
key: PageCacheKey,
page: PageRef,
ref_bit: u8,
}
let survivors: Vec<Payload> = {
let mut v = Vec::with_capacity(self.len());
let start = self.clock_hand;
if start != NULL {
let mut cur = start;
let mut seen = 0usize;
loop {
let e = &self.entries[cur];
if let Some(ref p) = e.page {
v.push(Payload {
key: e.key,
page: p.clone(),
ref_bit: e.ref_bit,
});
seen += 1;
}
cur = e.next;
if cur == start || seen >= self.len() {
break;
}
}
}
v
};
// Rebuild storage
self.entries.resize(new_cap, PageCacheEntry::empty());
self.capacity = new_cap;
let mut new_map = PageHashMap::new(new_cap);
let used = survivors.len().min(new_cap);
for (i, item) in survivors.iter().enumerate().take(used) {
let e = &mut self.entries[i];
e.key = item.key;
e.page = Some(item.page.clone());
e.ref_bit = item.ref_bit;
// link circularly to neighbors by index
let prev = if i == 0 { used - 1 } else { i - 1 };
let next = if i + 1 == used { 0 } else { i + 1 };
e.prev = prev;
e.next = next;
new_map.insert(item.key, i);
}
self.map = new_map;
// hand points to slot 0 if there are survivors, else NULL
self.clock_hand = if used > 0 { 0 } else { NULL };
// rebuild freelist
self.freelist.clear();
for i in (used..new_cap).rev() {
self.freelist.push(i);
}
CacheResizeResult::Done
}
/// Ensures at least `n` free slots are available
///
/// Uses the SIEVE algorithm to evict pages if necessary:
/// Start at tail (LRU position)
/// If page is marked, decrement mark
/// If page mark was already Cleared, evict it
/// If page is unevictable (dirty/locked/pinned), continue sweep
/// On sweep, pages with ref_bit > 0 are given a second chance by decrementing
/// their ref_bit and leaving them in place; only pages with ref_bit == 0 are evicted.
/// We never relocate nodes during sweeping.
/// because the list is circular, `tail.next == head` and `head.prev == tail`.
///
/// Returns `CacheError::Full` if not enough pages can be evicted
pub fn make_room_for(&mut self, n: usize) -> Result<(), CacheError> {
if n > self.capacity {
return Err(CacheError::Full);
}
let available = self.capacity - self.len();
if n <= available {
return Ok(());
}
let mut need = n - available;
let mut examined = 0usize;
let max_examinations = self.len().saturating_mul(REF_MAX as usize + 1);
let mut cur = self.clock_hand;
if cur == NULL || cur >= self.capacity || self.entries[cur].page.is_none() {
return Err(CacheError::Full);
}
while need > 0 && examined < max_examinations {
// compute the next candidate before mutating anything
let next = self.forward_of(cur);
let evictable_and_clear = {
let e = &mut self.entries[cur];
if let Some(ref p) = e.page {
if p.is_dirty() || p.is_locked() || p.is_pinned() {
examined += 1;
false
} else if e.ref_bit == CLEAR {
true
} else {
e.decrement_ref();
examined += 1;
false
}
} else {
examined += 1;
false
}
};
if evictable_and_clear {
// Evict the current slot, then continue from the next candidate in sweep direction
self.evict_slot(cur, true)?;
need -= 1;
examined = 0;
// move on; if the ring became empty, self.clock_hand may be NULL
cur = if next == cur { self.clock_hand } else { next };
if cur == NULL {
if need == 0 {
break;
}
return Err(CacheError::Full);
}
} else {
// keep sweeping
cur = next;
}
}
self.clock_hand = cur;
if need > 0 {
return Err(CacheError::Full);
}
Ok(())
}
pub fn clear(&mut self) -> Result<(), CacheError> {
if self.map.len() == 0 {
// Fast path: nothing to do.
self.clock_hand = NULL;
return Ok(());
}
for node in self.map.iter() {
let e = &self.entries[node.slot_index];
if let Some(ref p) = e.page {
if p.is_dirty() {
return Err(CacheError::Dirty { pgno: p.get().id });
}
}
}
let mut used_slots = Vec::with_capacity(self.map.len());
for node in self.map.iter() {
used_slots.push(node.slot_index);
}
// don't touch already-free slots at all.
for &i in &used_slots {
if let Some(p) = self.entries[i].page.take() {
p.clear_loaded();
let _ = p.get().contents.take();
}
self.entries[i].clear_ref();
self.entries[i].reset_links();
}
self.clock_hand = NULL;
self.map = PageHashMap::new(self.capacity);
for &i in used_slots.iter().rev() {
self.freelist.push(i);
}
Ok(())
}
#[inline]
/// preconditions: slot contains Some(page) and is clean/unlocked/unpinned
fn evict_slot(&mut self, slot: usize, clean_page: bool) -> Result<(), CacheError> {
let key = self.entries[slot].key;
if clean_page {
if let Some(ref p) = self.entries[slot].page {
p.clear_loaded();
let _ = p.get().contents.take();
}
}
// unlink will advance the hand if it pointed to `slot`
self.unlink(slot);
let _ = self.map.remove(&key);
let e = &mut self.entries[slot];
e.page = None;
e.clear_ref();
e.reset_links();
self.freelist.push(slot);
Ok(())
}
/// Removes all pages from the cache with pgno greater than len
pub fn truncate(&mut self, len: usize) -> Result<(), CacheError> {
let keys_to_delete: Vec<PageCacheKey> = {
self.entries
.iter()
.filter_map(|entry| {
entry.page.as_ref().and({
if entry.key.0 > len {
Some(entry.key)
} else {
None
}
})
})
.collect()
};
for key in keys_to_delete.iter() {
self.delete(*key)?;
}
Ok(())
}
pub fn print(&self) {
tracing::debug!("page_cache_len={}", self.map.len());
let entries = &self.entries;
for (i, entry_opt) in entries.iter().enumerate() {
if let Some(ref page) = entry_opt.page {
tracing::debug!(
"slot={}, page={:?}, flags={}, pin_count={}, ref_bit={:?}",
i,
entry_opt.key,
page.get().flags.load(Ordering::SeqCst),
page.get().pin_count.load(Ordering::SeqCst),
entry_opt.ref_bit,
);
}
}
}
#[cfg(test)]
pub fn keys(&mut self) -> Vec<PageCacheKey> {
let mut keys = Vec::with_capacity(self.len());
let entries = &self.entries;
for entry in entries.iter() {
if entry.page.is_none() {
continue;
}
keys.push(entry.key);
}
keys
}
pub fn len(&self) -> usize {
self.map.len()
}
pub fn capacity(&self) -> usize {
self.capacity
}
#[cfg(test)]
fn verify_cache_integrity(&self) {
let map = &self.map;
let hand = self.clock_hand;
if hand == NULL {
assert_eq!(map.len(), 0, "map not empty but list is empty");
} else {
// 0 = unseen, 1 = freelist, 2 = in list
let mut seen = vec![0u8; self.capacity];
// Walk exactly map.len steps from hand, ensure circular closure
let mut cnt = 0usize;
let mut cur = hand;
loop {
let e = &self.entries[cur];
assert!(e.page.is_some(), "list points to empty slot {cur}");
assert_eq!(seen[cur], 0, "slot {cur} appears twice (list/freelist)");
seen[cur] = 2;
cnt += 1;
let n = e.next;
let p = e.prev;
assert_eq!(self.entries[n].prev, cur, "broken next.prev at {cur}");
assert_eq!(self.entries[p].next, cur, "broken prev.next at {cur}");
if n == hand {
break;
}
assert!(cnt <= map.len(), "cycle longer than map len");
cur = n;
}
assert_eq!(
cnt,
map.len(),
"list length {} != map size {}",
cnt,
map.len()
);
// Map bijection
for node in map.iter() {
let slot = node.slot_index;
assert!(
self.entries[slot].page.is_some(),
"map points to empty slot"
);
assert_eq!(self.entries[slot].key, node.key, "map key mismatch");
assert_eq!(seen[slot], 2, "map slot {slot} not on list");
}
// Freelist disjointness
let mut free_count = 0usize;
for &s in &self.freelist {
free_count += 1;
assert_eq!(seen[s], 0, "slot {s} in both freelist and list");
assert!(
self.entries[s].page.is_none(),
"freelist slot {s} has a page"
);
assert_eq!(self.entries[s].next, NULL, "freelist slot {s} next != NULL");
assert_eq!(self.entries[s].prev, NULL, "freelist slot {s} prev != NULL");
seen[s] = 1;
}
// No orphans: every slot is in list or freelist or unused beyond capacity
let orphans = seen.iter().filter(|&&v| v == 0).count();
assert_eq!(
free_count + cnt + orphans,
self.capacity,
"free {} + list {} + orphans {} != capacity {}",
free_count,
cnt,
orphans,
self.capacity
);
// In practice orphans==0; assertion above detects mismatches.
}
// Hand sanity
if hand != NULL {
assert!(hand < self.capacity, "clock_hand out of bounds");
assert!(
self.entries[hand].page.is_some(),
"clock_hand points to empty slot"
);
}
}
#[cfg(test)]
fn slot_of(&self, key: &PageCacheKey) -> Option<usize> {
self.map.get(key)
}
#[cfg(test)]
fn ref_of(&self, key: &PageCacheKey) -> Option<u8> {
self.slot_of(key).map(|i| self.entries[i].ref_bit)
}
}
impl Default for PageCache {
fn default() -> Self {
PageCache::new(
DEFAULT_PAGE_CACHE_SIZE_IN_PAGES_MAKE_ME_SMALLER_ONCE_WAL_SPILL_IS_IMPLEMENTED,
)
}
}
#[derive(Clone)]
struct HashMapNode {
key: PageCacheKey,
slot_index: usize,
}
#[allow(dead_code)]
impl PageHashMap {
pub fn new(capacity: usize) -> PageHashMap {
PageHashMap {
buckets: vec![vec![]; capacity],
capacity,
size: 0,
}
}
pub fn insert(&mut self, key: PageCacheKey, slot_index: usize) {
let bucket = self.hash(&key);
let bucket = &mut self.buckets[bucket];
let mut idx = 0;
while let Some(node) = bucket.get_mut(idx) {
if node.key == key {
node.slot_index = slot_index;
node.key = key;
return;
}
idx += 1;
}
bucket.push(HashMapNode { key, slot_index });
self.size += 1;
}
pub fn contains_key(&self, key: &PageCacheKey) -> bool {
let bucket = self.hash(key);
self.buckets[bucket].iter().any(|node| node.key == *key)
}
pub fn get(&self, key: &PageCacheKey) -> Option<usize> {
let bucket = self.hash(key);
let bucket = &self.buckets[bucket];
for node in bucket {
if node.key == *key {
return Some(node.slot_index);
}
}
None
}
pub fn remove(&mut self, key: &PageCacheKey) -> Option<usize> {
let bucket = self.hash(key);
let bucket = &mut self.buckets[bucket];
let mut idx = 0;
while let Some(node) = bucket.get(idx) {
if node.key == *key {
break;
}
idx += 1;
}
if idx == bucket.len() {
None
} else {
let v = bucket.remove(idx);
self.size -= 1;
Some(v.slot_index)
}
}
pub fn clear(&mut self) {
for bucket in &mut self.buckets {
bucket.clear();
}
self.size = 0;
}
pub fn len(&self) -> usize {
self.size
}
fn iter(&self) -> impl Iterator<Item = &HashMapNode> {
self.buckets.iter().flat_map(|b| b.iter())
}
fn hash(&self, key: &PageCacheKey) -> usize {
if self.capacity.is_power_of_two() {
key.0 & (self.capacity - 1)
} else {
key.0 % self.capacity
}
}
fn rehash(&self, new_capacity: usize) -> PageHashMap {
let mut new_hash_map = PageHashMap::new(new_capacity);
for node in self.iter() {
new_hash_map.insert(node.key, node.slot_index);
}
new_hash_map
}
}
#[cfg(test)]
mod tests {
use super::*;
use crate::storage::page_cache::CacheError;
use crate::storage::pager::{Page, PageRef};
use crate::storage::sqlite3_ondisk::PageContent;
use rand_chacha::{
rand_core::{RngCore, SeedableRng},
ChaCha8Rng,
};
use std::sync::Arc;
fn create_key(id: usize) -> PageCacheKey {
PageCacheKey::new(id)
}
pub fn page_with_content(page_id: usize) -> PageRef {
let page = Arc::new(Page::new(page_id));
{
let buffer = crate::Buffer::new_temporary(4096);
let page_content = PageContent {
offset: 0,
buffer: Arc::new(buffer),
overflow_cells: Vec::new(),
};
page.get().contents = Some(page_content);
page.set_loaded();
}
page
}
fn insert_page(cache: &mut PageCache, id: usize) -> PageCacheKey {
let key = create_key(id);
let page = page_with_content(id);
assert!(cache.insert(key, page).is_ok());
key
}
#[test]
fn test_delete_only_element() {
let mut cache = PageCache::default();
let key1 = insert_page(&mut cache, 1);
cache.verify_cache_integrity();
assert_eq!(cache.len(), 1);
assert!(cache.delete(key1).is_ok());
assert_eq!(
cache.len(),
0,
"Length should be 0 after deleting only element"
);
assert!(
!cache.contains_key(&key1),
"Cache should not contain key after delete"
);
cache.verify_cache_integrity();
}
#[test]
fn test_detach_tail() {
let mut cache = PageCache::default();
let key1 = insert_page(&mut cache, 1); // tail
let _key2 = insert_page(&mut cache, 2); // middle
let _key3 = insert_page(&mut cache, 3); // head
cache.verify_cache_integrity();
assert_eq!(cache.len(), 3);
// Delete tail
assert!(cache.delete(key1).is_ok());
assert_eq!(cache.len(), 2, "Length should be 2 after deleting tail");
assert!(
!cache.contains_key(&key1),
"Cache should not contain deleted tail key"
);
cache.verify_cache_integrity();
}
#[test]
fn test_insert_existing_key_updates_in_place() {
let mut cache = PageCache::default();
let key1 = create_key(1);
let page1_v1 = page_with_content(1);
let page1_v2 = page1_v1.clone(); // Same Arc instance
assert!(cache.insert(key1, page1_v1.clone()).is_ok());
assert_eq!(cache.len(), 1);
// Inserting same page instance should return KeyExists error
let result = cache.insert(key1, page1_v2.clone());
assert_eq!(result, Err(CacheError::KeyExists));
assert_eq!(cache.len(), 1);
// Verify the page is still accessible
assert!(cache.get(&key1).unwrap().is_some());
cache.verify_cache_integrity();
}
#[test]
#[should_panic(expected = "Attempted to insert different page with same key")]
fn test_insert_different_page_same_key_panics() {
let mut cache = PageCache::default();
let key1 = create_key(1);
let page1_v1 = page_with_content(1);
let page1_v2 = page_with_content(1); // Different Arc instance
assert!(cache.insert(key1, page1_v1.clone()).is_ok());
assert_eq!(cache.len(), 1);
cache.verify_cache_integrity();
// This should panic because it's a different page instance
let _ = cache.insert(key1, page1_v2.clone());
}
#[test]
fn test_delete_nonexistent_key() {
let mut cache = PageCache::default();
let key_nonexist = create_key(99);
// Deleting non-existent key should be a no-op (returns Ok)
assert!(cache.delete(key_nonexist).is_ok());
assert_eq!(cache.len(), 0);
cache.verify_cache_integrity();
}
#[test]
fn test_page_cache_evict() {
let mut cache = PageCache::new(1);
let key1 = insert_page(&mut cache, 1);
let key2 = insert_page(&mut cache, 2);
// With capacity=1, inserting key2 should evict key1
assert_eq!(cache.get(&key2).unwrap().unwrap().get().id, 2);
assert!(
cache.get(&key1).unwrap().is_none(),
"key1 should be evicted"
);
// key2 should still be accessible
assert_eq!(cache.get(&key2).unwrap().unwrap().get().id, 2);
assert!(
cache.get(&key1).unwrap().is_none(),
"capacity=1 should have evicted the older page"
);
cache.verify_cache_integrity();
}
#[test]
fn test_sieve_touch_non_tail_does_not_affect_immediate_eviction() {
// SIEVE algorithm: touching a non-tail page marks it but doesn't move it.
// The tail (if unmarked) will still be the first eviction candidate.
// Insert 1,2,3 -> order [3,2,1] with tail=1
let mut cache = PageCache::new(3);
let key1 = insert_page(&mut cache, 1);
let key2 = insert_page(&mut cache, 2);
let key3 = insert_page(&mut cache, 3);
// Touch key2 (middle) to mark it with reference bit
assert!(cache.get(&key2).unwrap().is_some());
// Insert 4: SIEVE examines tail (key1, unmarked) -> evict key1
let key4 = insert_page(&mut cache, 4);
assert!(
cache.get(&key2).unwrap().is_some(),
"marked non-tail (key2) should remain"
);
assert!(cache.get(&key3).unwrap().is_some(), "key3 should remain");
assert!(
cache.get(&key4).unwrap().is_some(),
"key4 was just inserted"
);
assert!(
cache.get(&key1).unwrap().is_none(),
"unmarked tail (key1) should be evicted first"
);
cache.verify_cache_integrity();
}
#[test]
fn clock_second_chance_decrements_tail_then_evicts_next() {
let mut cache = PageCache::new(3);
let key1 = insert_page(&mut cache, 1);
let key2 = insert_page(&mut cache, 2);
let key3 = insert_page(&mut cache, 3);
assert_eq!(cache.len(), 3);
assert!(cache.get(&key1).unwrap().is_some());
let key4 = insert_page(&mut cache, 4);
assert!(cache.get(&key1).unwrap().is_some(), "key1 should survive");
assert!(cache.get(&key2).unwrap().is_some(), "key2 remains");
assert!(cache.get(&key4).unwrap().is_some(), "key4 inserted");
assert!(
cache.get(&key3).unwrap().is_none(),
"key3 (next after tail) evicted"
);
assert_eq!(cache.len(), 3);
cache.verify_cache_integrity();
}
#[test]
fn test_delete_locked_page() {
let mut cache = PageCache::default();
let key = insert_page(&mut cache, 1);
let page = cache.get(&key).unwrap().unwrap();
page.set_locked();
assert_eq!(cache.delete(key), Err(CacheError::Locked { pgno: 1 }));
assert_eq!(cache.len(), 1, "Locked page should not be deleted");
cache.verify_cache_integrity();
}
#[test]
fn test_delete_dirty_page() {
let mut cache = PageCache::default();
let key = insert_page(&mut cache, 1);
let page = cache.get(&key).unwrap().unwrap();
page.set_dirty();
assert_eq!(cache.delete(key), Err(CacheError::Dirty { pgno: 1 }));
assert_eq!(cache.len(), 1, "Dirty page should not be deleted");
cache.verify_cache_integrity();
}
#[test]
fn test_delete_pinned_page() {
let mut cache = PageCache::default();
let key = insert_page(&mut cache, 1);
let page = cache.get(&key).unwrap().unwrap();
page.pin();
assert_eq!(cache.delete(key), Err(CacheError::Pinned { pgno: 1 }));
assert_eq!(cache.len(), 1, "Pinned page should not be deleted");
cache.verify_cache_integrity();
}
#[test]
fn test_make_room_for_with_dirty_pages() {
let mut cache = PageCache::new(2);
let key1 = insert_page(&mut cache, 1);
let key2 = insert_page(&mut cache, 2);
// Make both pages dirty (unevictable)
cache.get(&key1).unwrap().unwrap().set_dirty();
cache.get(&key2).unwrap().unwrap().set_dirty();
// Try to insert a third page, should fail because can't evict dirty pages
let key3 = create_key(3);
let page3 = page_with_content(3);
let result = cache.insert(key3, page3);
assert_eq!(result, Err(CacheError::Full));
assert_eq!(cache.len(), 2);
cache.verify_cache_integrity();
}
#[test]
fn test_page_cache_insert_and_get() {
let mut cache = PageCache::default();
let key1 = insert_page(&mut cache, 1);
let key2 = insert_page(&mut cache, 2);
assert_eq!(cache.get(&key1).unwrap().unwrap().get().id, 1);
assert_eq!(cache.get(&key2).unwrap().unwrap().get().id, 2);
cache.verify_cache_integrity();
}
#[test]
fn test_page_cache_over_capacity() {
// Test SIEVE eviction when exceeding capacity
let mut cache = PageCache::new(2);
let key1 = insert_page(&mut cache, 1);
let key2 = insert_page(&mut cache, 2);
// Insert 3: tail (key1, unmarked) should be evicted
let key3 = insert_page(&mut cache, 3);
assert_eq!(cache.len(), 2);
assert!(cache.get(&key2).unwrap().is_some(), "key2 should remain");
assert!(cache.get(&key3).unwrap().is_some(), "key3 just inserted");
assert!(
cache.get(&key1).unwrap().is_none(),
"key1 (oldest, unmarked) should be evicted"
);
cache.verify_cache_integrity();
}
#[test]
fn test_page_cache_delete() {
let mut cache = PageCache::default();
let key1 = insert_page(&mut cache, 1);
assert!(cache.delete(key1).is_ok());
assert!(cache.get(&key1).unwrap().is_none());
assert_eq!(cache.len(), 0);
cache.verify_cache_integrity();
}
#[test]
fn test_page_cache_clear() {
let mut cache = PageCache::default();
let key1 = insert_page(&mut cache, 1);
let key2 = insert_page(&mut cache, 2);
assert!(cache.clear().is_ok());
assert!(cache.get(&key1).unwrap().is_none());
assert!(cache.get(&key2).unwrap().is_none());
assert_eq!(cache.len(), 0);
cache.verify_cache_integrity();
}
#[test]
fn test_resize_smaller_success() {
let mut cache = PageCache::default();
for i in 1..=5 {
let _ = insert_page(&mut cache, i);
}
assert_eq!(cache.len(), 5);
let result = cache.resize(3);
assert_eq!(result, CacheResizeResult::Done);
assert_eq!(cache.len(), 3);
assert_eq!(cache.capacity(), 3);
// Should still be able to insert after resize
assert!(cache.insert(create_key(6), page_with_content(6)).is_ok());
assert_eq!(cache.len(), 3); // One was evicted to make room
cache.verify_cache_integrity();
}
#[test]
fn test_detach_with_multiple_pages() {
let mut cache = PageCache::default();
let _key1 = insert_page(&mut cache, 1);
let key2 = insert_page(&mut cache, 2);
let _key3 = insert_page(&mut cache, 3);
// Delete middle element (key2)
assert!(cache.delete(key2).is_ok());
// Verify structure after deletion
assert_eq!(cache.len(), 2);
assert!(!cache.contains_key(&key2));
cache.verify_cache_integrity();
}
#[test]
fn test_delete_multiple_elements() {
let mut cache = PageCache::default();
let key1 = insert_page(&mut cache, 1);
let key2 = insert_page(&mut cache, 2);
let key3 = insert_page(&mut cache, 3);
cache.verify_cache_integrity();
assert_eq!(cache.len(), 3);
// Delete head (key3)
assert!(cache.delete(key3).is_ok());
assert_eq!(cache.len(), 2, "Length should be 2 after deleting head");
assert!(
!cache.contains_key(&key3),
"Cache should not contain deleted head key"
);
cache.verify_cache_integrity();
// Delete tail (key1)
assert!(cache.delete(key1).is_ok());
assert_eq!(cache.len(), 1, "Length should be 1 after deleting two");
cache.verify_cache_integrity();
// Delete last element (key2)
assert!(cache.delete(key2).is_ok());
assert_eq!(cache.len(), 0, "Length should be 0 after deleting all");
cache.verify_cache_integrity();
}
#[test]
fn test_resize_larger() {
let mut cache = PageCache::new(2);
let key1 = insert_page(&mut cache, 1);
let key2 = insert_page(&mut cache, 2);
assert_eq!(cache.len(), 2);
let result = cache.resize(5);
assert_eq!(result, CacheResizeResult::Done);
assert_eq!(cache.len(), 2);
assert_eq!(cache.capacity(), 5);
// Existing pages should still be accessible
assert!(cache.get(&key1).is_ok_and(|p| p.is_some()));
assert!(cache.get(&key2).is_ok_and(|p| p.is_some()));
// Now we should be able to add 3 more without eviction
for i in 3..=5 {
let _ = insert_page(&mut cache, i);
}
assert_eq!(cache.len(), 5);
cache.verify_cache_integrity();
}
#[test]
fn test_resize_same_capacity() {
let mut cache = PageCache::new(3);
for i in 1..=3 {
let _ = insert_page(&mut cache, i);
}
let result = cache.resize(3);
assert_eq!(result, CacheResizeResult::Done);
assert_eq!(cache.len(), 3);
assert_eq!(cache.capacity(), 3);
cache.verify_cache_integrity();
}
#[test]
fn test_truncate_page_cache() {
let mut cache = PageCache::new(10);
let _ = insert_page(&mut cache, 1);
let _ = insert_page(&mut cache, 4);
let _ = insert_page(&mut cache, 8);
let _ = insert_page(&mut cache, 10);
// Truncate to keep only pages <= 4
cache.truncate(4).unwrap();
assert!(cache.contains_key(&PageCacheKey(1)));
assert!(cache.contains_key(&PageCacheKey(4)));
assert!(!cache.contains_key(&PageCacheKey(8)));
assert!(!cache.contains_key(&PageCacheKey(10)));
assert_eq!(cache.len(), 2);
assert_eq!(cache.capacity(), 10);
cache.verify_cache_integrity();
}
#[test]
fn test_truncate_page_cache_remove_all() {
let mut cache = PageCache::new(10);
let _ = insert_page(&mut cache, 8);
let _ = insert_page(&mut cache, 10);
// Truncate to 4 (removes all pages since they're > 4)
cache.truncate(4).unwrap();
assert!(!cache.contains_key(&PageCacheKey(8)));
assert!(!cache.contains_key(&PageCacheKey(10)));
assert_eq!(cache.len(), 0);
assert_eq!(cache.capacity(), 10);
cache.verify_cache_integrity();
}
#[test]
fn test_page_cache_fuzz() {
let seed = std::time::SystemTime::now()
.duration_since(std::time::UNIX_EPOCH)
.unwrap()
.as_secs();
let mut rng = ChaCha8Rng::seed_from_u64(seed);
tracing::info!("fuzz test seed: {}", seed);
let max_pages = 10;
let mut cache = PageCache::new(10);
let mut reference_map = std::collections::HashMap::new();
for _ in 0..10000 {
cache.print();
match rng.next_u64() % 2 {
0 => {
// Insert operation
let id_page = rng.next_u64() % max_pages;
let key = PageCacheKey::new(id_page as usize);
#[allow(clippy::arc_with_non_send_sync)]
let page = Arc::new(Page::new(id_page as usize));
if cache.peek(&key, false).is_some() {
continue; // Skip duplicate page ids
}
tracing::debug!("inserting page {:?}", key);
match cache.insert(key, page.clone()) {
Err(CacheError::Full | CacheError::ActiveRefs) => {} // Expected, ignore
Err(err) => {
panic!("Cache insertion failed unexpectedly: {err:?}");
}
Ok(_) => {
reference_map.insert(key, page);
// Clean up reference_map if cache evicted something
if cache.len() < reference_map.len() {
reference_map.retain(|k, _| cache.contains_key(k));
}
}
}
assert!(cache.len() <= 10, "Cache size exceeded capacity");
}
1 => {
// Delete operation
let random = rng.next_u64() % 2 == 0;
let key = if random || reference_map.is_empty() {
let id_page: u64 = rng.next_u64() % max_pages;
PageCacheKey::new(id_page as usize)
} else {
let i = rng.next_u64() as usize % reference_map.len();
*reference_map.keys().nth(i).unwrap()
};
tracing::debug!("removing page {:?}", key);
reference_map.remove(&key);
assert!(cache.delete(key).is_ok());
}
_ => unreachable!(),
}
cache.verify_cache_integrity();
// Verify all pages in reference_map are in cache
for (key, page) in &reference_map {
let cached_page = cache.peek(key, false).expect("Page should be in cache");
assert_eq!(cached_page.get().id, key.0);
assert_eq!(page.get().id, key.0);
}
}
}
#[test]
fn test_peek_without_touch() {
// Test that peek with touch=false doesn't mark pages
let mut cache = PageCache::new(2);
let key1 = insert_page(&mut cache, 1);
let key2 = insert_page(&mut cache, 2);
// Peek key1 without touching (no ref bit set)
assert!(cache.peek(&key1, false).is_some());
// Insert 3: should evict unmarked tail (key1)
let key3 = insert_page(&mut cache, 3);
assert!(cache.get(&key2).unwrap().is_some(), "key2 should remain");
assert!(
cache.get(&key3).unwrap().is_some(),
"key3 was just inserted"
);
assert!(
cache.get(&key1).unwrap().is_none(),
"key1 should be evicted since peek(false) didn't mark it"
);
assert_eq!(cache.len(), 2);
cache.verify_cache_integrity();
}
#[test]
fn test_peek_with_touch() {
// Test that peek with touch=true marks pages for SIEVE
let mut cache = PageCache::new(2);
let key1 = insert_page(&mut cache, 1);
let key2 = insert_page(&mut cache, 2);
// Peek key1 WITH touching (sets ref bit)
assert!(cache.peek(&key1, true).is_some());
// Insert 3: key1 is marked, so it gets second chance
// key2 becomes new tail and gets evicted
let key3 = insert_page(&mut cache, 3);
assert!(
cache.get(&key1).unwrap().is_some(),
"key1 should survive (was marked)"
);
assert!(
cache.get(&key3).unwrap().is_some(),
"key3 was just inserted"
);
assert!(
cache.get(&key2).unwrap().is_none(),
"key2 should be evicted after key1's second chance"
);
assert_eq!(cache.len(), 2);
cache.verify_cache_integrity();
}
#[test]
#[ignore = "long running test, remove ignore to verify memory stability"]
fn test_clear_memory_stability() {
let initial_memory = memory_stats::memory_stats().unwrap().physical_mem;
for _ in 0..100000 {
let mut cache = PageCache::new(1000);
for i in 0..1000 {
let key = create_key(i);
let page = page_with_content(i);
cache.insert(key, page).unwrap();
}
cache.clear().unwrap();
drop(cache);
}
let final_memory = memory_stats::memory_stats().unwrap().physical_mem;
let growth = final_memory.saturating_sub(initial_memory);
println!("Memory growth: {growth} bytes");
assert!(
growth < 10_000_000,
"Memory grew by {growth} bytes over test cycles (limit: 10MB)",
);
}
#[test]
fn clock_drains_hot_page_within_single_sweep_when_others_are_unevictable() {
// capacity 3: [3(head), 2, 1(tail)]
let mut c = PageCache::new(3);
let k1 = insert_page(&mut c, 1);
let k2 = insert_page(&mut c, 2);
let _k3 = insert_page(&mut c, 3);
// Make k1 hot: bump to Max
for _ in 0..3 {
assert!(c.get(&k1).unwrap().is_some());
}
assert!(matches!(c.ref_of(&k1), Some(REF_MAX)));
// Make other pages unevictable; clock must keep revisiting k1.
c.get(&k2).unwrap().unwrap().set_dirty();
c.get(&_k3).unwrap().unwrap().set_dirty();
// Insert 4 -> sweep rotates as needed, draining k1 and evicting it.
let _k4 = insert_page(&mut c, 4);
assert!(
c.get(&k1).unwrap().is_none(),
"k1 should be evicted after its credit drains"
);
assert!(c.get(&k2).unwrap().is_some(), "k2 is dirty (unevictable)");
assert!(c.get(&_k3).unwrap().is_some(), "k3 is dirty (unevictable)");
assert!(c.get(&_k4).unwrap().is_some(), "k4 just inserted");
c.verify_cache_integrity();
}
#[test]
fn gclock_hot_survives_scan_pages() {
let mut c = PageCache::new(4);
let _k1 = insert_page(&mut c, 1);
let k2 = insert_page(&mut c, 2);
let _k3 = insert_page(&mut c, 3);
let _k4 = insert_page(&mut c, 4);
// Make k2 truly hot: three real touches
for _ in 0..3 {
assert!(c.get(&k2).unwrap().is_some());
}
assert!(matches!(c.ref_of(&k2), Some(REF_MAX)));
// Now simulate a scan inserting new pages 5..10 (one-hit wonders).
for id in 5..=10 {
let _ = insert_page(&mut c, id);
}
// Hot k2 should still be present; most single-hit scan pages should churn.
assert!(
c.get(&k2).unwrap().is_some(),
"hot page should survive scan"
);
// The earliest single-hit page should be gone.
assert!(c.get(&create_key(5)).unwrap().is_none());
c.verify_cache_integrity();
}
#[test]
fn hand_stays_valid_after_deleting_only_element() {
let mut c = PageCache::new(2);
let k = insert_page(&mut c, 1);
assert!(c.delete(k).is_ok());
// Inserting again should not panic and should succeed
let _ = insert_page(&mut c, 2);
c.verify_cache_integrity();
}
#[test]
fn hand_is_reset_after_clear_and_resize() {
let mut c = PageCache::new(3);
for i in 1..=3 {
let _ = insert_page(&mut c, i);
}
c.clear().unwrap();
// No elements; insert should not rely on stale hand
let _ = insert_page(&mut c, 10);
// Resize from 1 -> 4 and back should not OOB the hand
assert_eq!(c.resize(4), CacheResizeResult::Done);
assert_eq!(c.resize(1), CacheResizeResult::Done);
let _ = insert_page(&mut c, 11);
c.verify_cache_integrity();
}
#[test]
fn resize_preserves_ref_and_recency() {
let mut c = PageCache::new(4);
let _k1 = insert_page(&mut c, 1);
let k2 = insert_page(&mut c, 2);
let _k3 = insert_page(&mut c, 3);
let _k4 = insert_page(&mut c, 4);
// Make k2 hot.
for _ in 0..3 {
assert!(c.get(&k2).unwrap().is_some());
}
let _r_before = c.ref_of(&k2);
// Shrink to 3 (one page will be evicted during repack/next insert)
assert_eq!(c.resize(3), CacheResizeResult::Done);
assert!(matches!(c.ref_of(&k2), _r_before));
// Force an eviction; hot k2 should survive more passes.
let _ = insert_page(&mut c, 5);
assert!(c.get(&k2).unwrap().is_some());
c.verify_cache_integrity();
}
#[test]
fn test_sieve_second_chance_preserves_marked_page() {
let mut cache = PageCache::new(3);
let key1 = insert_page(&mut cache, 1);
let key2 = insert_page(&mut cache, 2);
let key3 = insert_page(&mut cache, 3);
// Mark key1 for second chance
assert!(cache.get(&key1).unwrap().is_some());
let key4 = insert_page(&mut cache, 4);
// CLOCK sweep from hand:
// - key1 marked -> decrement, continue
// - key3 (MRU) unmarked -> evict
assert!(
cache.get(&key1).unwrap().is_some(),
"key1 had ref bit set, got second chance"
);
assert!(
cache.get(&key3).unwrap().is_none(),
"key3 (MRU) should be evicted"
);
assert!(cache.get(&key4).unwrap().is_some(), "key4 just inserted");
assert!(
cache.get(&key2).unwrap().is_some(),
"key2 (middle) should remain"
);
cache.verify_cache_integrity();
}
#[test]
fn test_clock_sweep_wraps_around() {
// Test that clock hand properly wraps around the circular list
let mut cache = PageCache::new(3);
let key1 = insert_page(&mut cache, 1);
let key2 = insert_page(&mut cache, 2);
let key3 = insert_page(&mut cache, 3);
// Mark all pages
assert!(cache.get(&key1).unwrap().is_some());
assert!(cache.get(&key2).unwrap().is_some());
assert!(cache.get(&key3).unwrap().is_some());
// Insert 4: hand will sweep full circle, decrementing all refs
// then sweep again and evict first unmarked page
let key4 = insert_page(&mut cache, 4);
// One page was evicted after full sweep
assert_eq!(cache.len(), 3);
assert!(cache.get(&key4).unwrap().is_some());
// Verify exactly one of the original pages was evicted
let survivors = [key1, key2, key3]
.iter()
.filter(|k| cache.get(k).unwrap().is_some())
.count();
assert_eq!(survivors, 2, "Should have 2 survivors from original 3");
cache.verify_cache_integrity();
}
#[test]
fn test_circular_list_single_element() {
let mut cache = PageCache::new(3);
let key1 = insert_page(&mut cache, 1);
// Single element should point to itself
let slot = cache.slot_of(&key1).unwrap();
assert_eq!(cache.entries[slot].next, slot);
assert_eq!(cache.entries[slot].prev, slot);
// Delete single element
assert!(cache.delete(key1).is_ok());
assert_eq!(cache.clock_hand, NULL);
// Insert after empty should work
let key2 = insert_page(&mut cache, 2);
let slot2 = cache.slot_of(&key2).unwrap();
assert_eq!(cache.entries[slot2].next, slot2);
assert_eq!(cache.entries[slot2].prev, slot2);
cache.verify_cache_integrity();
}
#[test]
fn test_hand_advances_on_eviction() {
let mut cache = PageCache::new(2);
let _key1 = insert_page(&mut cache, 1);
let _key2 = insert_page(&mut cache, 2);
// Note initial hand position
let initial_hand = cache.clock_hand;
// Force eviction
let _key3 = insert_page(&mut cache, 3);
// Hand should have advanced
let new_hand = cache.clock_hand;
assert_ne!(new_hand, NULL);
// Hand moved during sweep (exact position depends on eviction)
assert!(initial_hand == NULL || new_hand != initial_hand || cache.len() < 2);
cache.verify_cache_integrity();
}
#[test]
fn test_multi_level_ref_counting() {
let mut cache = PageCache::new(2);
let key1 = insert_page(&mut cache, 1);
let _key2 = insert_page(&mut cache, 2);
// Bump key1 to MAX (3 accesses)
for _ in 0..3 {
assert!(cache.get(&key1).unwrap().is_some());
}
assert_eq!(cache.ref_of(&key1), Some(REF_MAX));
// Insert multiple new pages - key1 should survive longer
for i in 3..6 {
let _ = insert_page(&mut cache, i);
}
// key1 might still be there due to high ref count
// (depends on exact sweep pattern, but it got multiple chances)
cache.verify_cache_integrity();
}
#[test]
fn test_resize_maintains_circular_structure() {
let mut cache = PageCache::new(5);
for i in 1..=4 {
let _ = insert_page(&mut cache, i);
}
// Resize smaller
assert_eq!(cache.resize(2), CacheResizeResult::Done);
assert_eq!(cache.len(), 2);
// Verify circular structure
if cache.clock_hand != NULL {
let start = cache.clock_hand;
let mut current = start;
let mut count = 0;
loop {
count += 1;
current = cache.entries[current].next;
if current == start {
break;
}
assert!(count <= cache.len(), "Circular list broken after resize");
}
assert_eq!(count, cache.len());
}
cache.verify_cache_integrity();
}
#[test]
fn test_link_after_correctness() {
let mut cache = PageCache::new(4);
let key1 = insert_page(&mut cache, 1);
let key2 = insert_page(&mut cache, 2);
let key3 = insert_page(&mut cache, 3);
// Verify circular linkage
let slot1 = cache.slot_of(&key1).unwrap();
let slot2 = cache.slot_of(&key2).unwrap();
let slot3 = cache.slot_of(&key3).unwrap();
// Should form a circle: 3 -> 2 -> 1 -> 3 (insertion order)
assert_eq!(cache.entries[slot3].next, slot2);
assert_eq!(cache.entries[slot2].next, slot1);
assert_eq!(cache.entries[slot1].next, slot3);
assert_eq!(cache.entries[slot3].prev, slot1);
assert_eq!(cache.entries[slot2].prev, slot3);
assert_eq!(cache.entries[slot1].prev, slot2);
cache.verify_cache_integrity();
}
}
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