mirror of
https://github.com/tursodatabase/limbo.git
synced 2025-08-04 01:58:16 +00:00
191 lines
5.5 KiB
Rust
191 lines
5.5 KiB
Rust
use std::{cell::RefCell, collections::HashMap, ptr::NonNull};
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use tracing::debug;
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use super::pager::PageRef;
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// In limbo, page cache is shared by default, meaning that multiple frames from WAL can reside in
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// the cache, meaning, we need a way to differentiate between pages cached in different
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// connections. For this we include the max_frame that a connection will read from so that if two
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// connections have different max_frames, they might or not have different frame read from WAL.
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//
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// WAL was introduced after Shared cache in SQLite, so this is why these two features don't work
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// well together because pages with different snapshots may collide.
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#[derive(Debug, Eq, Hash, PartialEq, Clone)]
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pub struct PageCacheKey {
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pgno: usize,
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max_frame: Option<u64>,
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}
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#[allow(dead_code)]
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struct PageCacheEntry {
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key: PageCacheKey,
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page: PageRef,
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prev: Option<NonNull<PageCacheEntry>>,
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next: Option<NonNull<PageCacheEntry>>,
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}
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impl PageCacheEntry {
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fn as_non_null(&mut self) -> NonNull<PageCacheEntry> {
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NonNull::new(&mut *self).unwrap()
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}
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}
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pub struct DumbLruPageCache {
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capacity: usize,
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map: RefCell<HashMap<PageCacheKey, NonNull<PageCacheEntry>>>,
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head: RefCell<Option<NonNull<PageCacheEntry>>>,
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tail: RefCell<Option<NonNull<PageCacheEntry>>>,
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}
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unsafe impl Send for DumbLruPageCache {}
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unsafe impl Sync for DumbLruPageCache {}
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impl PageCacheKey {
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pub fn new(pgno: usize, max_frame: Option<u64>) -> Self {
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Self { pgno, max_frame }
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}
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}
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impl DumbLruPageCache {
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pub fn new(capacity: usize) -> Self {
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Self {
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capacity,
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map: RefCell::new(HashMap::new()),
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head: RefCell::new(None),
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tail: RefCell::new(None),
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}
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}
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pub fn contains_key(&mut self, key: &PageCacheKey) -> bool {
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self.map.borrow().contains_key(key)
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}
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pub fn insert(&mut self, key: PageCacheKey, value: PageRef) {
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self._delete(key.clone(), false);
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debug!("cache_insert(key={:?})", key);
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let mut entry = Box::new(PageCacheEntry {
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key: key.clone(),
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next: None,
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prev: None,
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page: value,
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});
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self.touch(&mut entry);
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if self.map.borrow().len() >= self.capacity {
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self.pop_if_not_dirty();
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}
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let b = Box::into_raw(entry);
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let as_non_null = NonNull::new(b).unwrap();
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self.map.borrow_mut().insert(key, as_non_null);
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}
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pub fn delete(&mut self, key: PageCacheKey) {
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self._delete(key, true)
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}
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pub fn _delete(&mut self, key: PageCacheKey, clean_page: bool) {
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debug!("cache_delete(key={:?}, clean={})", key, clean_page);
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let ptr = self.map.borrow_mut().remove(&key);
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if ptr.is_none() {
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return;
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}
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let mut ptr = ptr.unwrap();
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{
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let ptr = unsafe { ptr.as_mut() };
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self.detach(ptr, clean_page);
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}
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unsafe { std::ptr::drop_in_place(ptr.as_ptr()) };
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}
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fn get_ptr(&mut self, key: &PageCacheKey) -> Option<NonNull<PageCacheEntry>> {
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let m = self.map.borrow_mut();
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let ptr = m.get(key);
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ptr.copied()
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}
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pub fn get(&mut self, key: &PageCacheKey) -> Option<PageRef> {
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debug!("cache_get(key={:?})", key);
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let ptr = self.get_ptr(key);
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ptr?;
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let ptr = unsafe { ptr.unwrap().as_mut() };
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let page = ptr.page.clone();
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//self.detach(ptr);
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self.touch(ptr);
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Some(page)
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}
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pub fn resize(&mut self, capacity: usize) {
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let _ = capacity;
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todo!();
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}
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fn detach(&mut self, entry: &mut PageCacheEntry, clean_page: bool) {
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let mut current = entry.as_non_null();
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if clean_page {
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// evict buffer
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let page = &entry.page;
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page.clear_loaded();
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debug!("cleaning up page {}", page.get().id);
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let _ = page.get().contents.take();
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}
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let (next, prev) = unsafe {
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let c = current.as_mut();
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let next = c.next;
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let prev = c.prev;
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c.prev = None;
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c.next = None;
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(next, prev)
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};
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// detach
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match (prev, next) {
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(None, None) => {}
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(None, Some(_)) => todo!(),
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(Some(p), None) => {
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self.tail = RefCell::new(Some(p));
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}
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(Some(mut p), Some(mut n)) => unsafe {
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let p_mut = p.as_mut();
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p_mut.next = Some(n);
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let n_mut = n.as_mut();
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n_mut.prev = Some(p);
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},
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};
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}
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fn touch(&mut self, entry: &mut PageCacheEntry) {
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let mut current = entry.as_non_null();
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unsafe {
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let c = current.as_mut();
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c.next = *self.head.borrow();
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}
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if let Some(mut head) = *self.head.borrow_mut() {
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unsafe {
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let head = head.as_mut();
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head.prev = Some(current);
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}
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}
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}
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fn pop_if_not_dirty(&mut self) {
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let tail = *self.tail.borrow();
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if tail.is_none() {
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return;
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}
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let tail = unsafe { tail.unwrap().as_mut() };
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if tail.page.is_dirty() {
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// TODO: drop from another clean entry?
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return;
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}
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self.detach(tail, true);
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}
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pub fn clear(&mut self) {
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let to_remove: Vec<PageCacheKey> = self.map.borrow().iter().map(|v| v.0.clone()).collect();
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for key in to_remove {
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self.delete(key);
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}
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}
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}
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