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page cache: add access & hit rate metrics (#4628)

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Co-authored-by: Dmitry Rodionov <dmitry@neon.tech>
This commit is contained in:
Christian Schwarz
2023-07-05 10:38:32 +02:00
committed by GitHub
parent c7143dbde6
commit 3f9defbfb4
3 changed files with 114 additions and 2 deletions
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41
pageserver/src/page_cache.rs
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@@ -313,6 +313,10 @@ impl PageCache {
key: &Key,
lsn: Lsn,
) -> Option<(Lsn, PageReadGuard)> {
crate::metrics::PAGE_CACHE
.read_accesses_materialized_page
.inc();
let mut cache_key = CacheKey::MaterializedPage {
hash_key: MaterializedPageHashKey {
tenant_id,
@@ -323,8 +327,21 @@ impl PageCache {
};
if let Some(guard) = self.try_lock_for_read(&mut cache_key) {
if let CacheKey::MaterializedPage { hash_key: _, lsn } = cache_key {
Some((lsn, guard))
if let CacheKey::MaterializedPage {
hash_key: _,
lsn: available_lsn,
} = cache_key
{
if available_lsn == lsn {
crate::metrics::PAGE_CACHE
.read_hits_materialized_page_exact
.inc();
} else {
crate::metrics::PAGE_CACHE
.read_hits_materialized_page_older_lsn
.inc();
}
Some((available_lsn, guard))
} else {
panic!("unexpected key type in slot");
}
@@ -499,11 +516,31 @@ impl PageCache {
/// ```
///
fn lock_for_read(&self, cache_key: &mut CacheKey) -> anyhow::Result<ReadBufResult> {
let (read_access, hit) = match cache_key {
CacheKey::MaterializedPage { .. } => {
unreachable!("Materialized pages use lookup_materialized_page")
}
CacheKey::EphemeralPage { .. } => (
&crate::metrics::PAGE_CACHE.read_accesses_ephemeral,
&crate::metrics::PAGE_CACHE.read_hits_ephemeral,
),
CacheKey::ImmutableFilePage { .. } => (
&crate::metrics::PAGE_CACHE.read_accesses_immutable,
&crate::metrics::PAGE_CACHE.read_hits_immutable,
),
};
read_access.inc();
let mut is_first_iteration = true;
loop {
// First check if the key already exists in the cache.
if let Some(read_guard) = self.try_lock_for_read(cache_key) {
if is_first_iteration {
hit.inc();
}
return Ok(ReadBufResult::Found(read_guard));
}
is_first_iteration = false;
// Not found. Find a victim buffer
let (slot_idx, mut inner) =