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page_cache: two-level immutable_page_map

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This change alone makes things strictly worse, but on top of this, we'll
be able to rewrite drop_buffers_for_immutable to remove pages based on
what's in the `drop_file_id`'s immutable_page_map second-level hash map.
That's better than what we do currently, i.e., iterating over all the
slots.
This commit is contained in:
Christian Schwarz
2023-08-28 18:35:32 +02:00
parent 529f8b5016
commit 8c933a9686
1 changed files with 32 additions and 7 deletions
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pageserver/src/page_cache.rs
+32 -7
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@@ -205,6 +205,8 @@ impl Slot {
}
}
type ImmutablePageMap = HashMap<FileId, RwLock<HashMap<u32, usize>>>;
pub struct PageCache {
/// This contains the mapping from the cache key to buffer slot that currently
/// contains the page, if any.
@@ -217,7 +219,7 @@ pub struct PageCache {
/// can have a separate mapping map, next to this field.
materialized_page_map: RwLock<HashMap<MaterializedPageHashKey, Vec<Version>>>,
immutable_page_map: RwLock<HashMap<(FileId, u32), usize>>,
immutable_page_map: RwLock<ImmutablePageMap>,
/// The actual buffers with their metadata.
slots: Box<[Slot]>,
@@ -657,7 +659,9 @@ impl PageCache {
}
CacheKey::ImmutableFilePage { file_id, blkno } => {
let map = self.immutable_page_map.read().unwrap();
Some(*map.get(&(*file_id, *blkno))?)
let block_nos = map.get(file_id)?;
let block_nos = block_nos.read().unwrap();
block_nos.get(blkno).copied()
}
}
}
@@ -680,7 +684,9 @@ impl PageCache {
}
CacheKey::ImmutableFilePage { file_id, blkno } => {
let map = self.immutable_page_map.read().unwrap();
Some(*map.get(&(*file_id, *blkno))?)
let block_nos = map.get(file_id)?;
let block_nos = block_nos.read().unwrap();
block_nos.get(blkno).copied()
}
}
}
@@ -712,10 +718,27 @@ impl PageCache {
}
}
CacheKey::ImmutableFilePage { file_id, blkno } => {
let mut map = self.immutable_page_map.write().unwrap();
map.remove(&(*file_id, *blkno))
.expect("could not find old key in mapping");
let map = self.immutable_page_map.read().unwrap();
let block_nos = map.get(file_id).expect("could not find file_id in mapping");
let mut block_nos = block_nos.write().unwrap();
block_nos
.remove(blkno)
.expect("could not find blkno in mapping");
self.size_metrics.current_bytes_immutable.sub_page_sz(1);
if block_nos.is_empty() {
drop(block_nos);
// re-lock map in write mode
drop(map);
let mut map = self.immutable_page_map.write().unwrap();
let Some(block_nos_rwl) = map.get(file_id) else {
return;
};
let block_nos = block_nos_rwl.read().unwrap();
if block_nos.is_empty() {
drop(block_nos);
map.remove(file_id);
}
}
}
}
}
@@ -753,7 +776,9 @@ impl PageCache {
CacheKey::ImmutableFilePage { file_id, blkno } => {
let mut map = self.immutable_page_map.write().unwrap();
match map.entry((*file_id, *blkno)) {
let block_nos = map.entry(*file_id).or_default();
let mut block_nos = block_nos.write().unwrap();
match block_nos.entry(*blkno) {
Entry::Occupied(entry) => Some(*entry.get()),
Entry::Vacant(entry) => {
entry.insert(slot_idx);