From be3c261715be543d7c406a3f7e33ba6c48de85e6 Mon Sep 17 00:00:00 2001
From: BodoBolero <peterbendel@neon.tech>
Date: Thu, 24 Apr 2025 14:59:02 +0200
Subject: [PATCH] use scc::HashMap instead of DashMap

---
 Cargo.lock                   | 17 ++++++++++++++++-
 Cargo.toml                   |  2 +-
 pageserver/Cargo.toml        |  2 +-
 pageserver/src/page_cache.rs |  8 ++++----
 4 files changed, 22 insertions(+), 7 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index 70fc9aebc8..178038bbf5 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -4262,7 +4262,6 @@ dependencies = [
  "consumption_metrics",
  "crc32c",
  "criterion",
- "dashmap 6.1.0",
  "either",
  "enum-map",
  "enumset",
@@ -4303,6 +4302,7 @@ dependencies = [
  "reqwest",
  "rpds",
  "rustls 0.23.18",
+ "scc",
  "scopeguard",
  "send-future",
  "serde",
@@ -6077,6 +6077,15 @@ dependencies = [
  "winapi-util",
 ]
 
+[[package]]
+name = "scc"
+version = "2.3.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "22b2d775fb28f245817589471dd49c5edf64237f4a19d10ce9a92ff4651a27f4"
+dependencies = [
+ "sdd",
+]
+
 [[package]]
 name = "schannel"
 version = "0.1.23"
@@ -6117,6 +6126,12 @@ version = "0.4.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "621e3680f3e07db4c9c2c3fb07c6223ab2fab2e54bd3c04c3ae037990f428c32"
 
+[[package]]
+name = "sdd"
+version = "3.0.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "584e070911c7017da6cb2eb0788d09f43d789029b5877d3e5ecc8acf86ceee21"
+
 [[package]]
 name = "sec1"
 version = "0.3.0"
diff --git a/Cargo.toml b/Cargo.toml
index 3a3716a08a..6453ecd3c7 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -85,7 +85,6 @@ clashmap = { version = "1.0", features = ["raw-api"] }
 comfy-table = "7.1"
 const_format = "0.2"
 crc32c = "0.6"
-dashmap = "6.1"
 diatomic-waker = { version = "0.2.3" }
 either = "1.8"
 enum-map = "2.4.2"
@@ -161,6 +160,7 @@ rustc-hash = "1.1.0"
 rustls = { version = "0.23.16", default-features = false }
 rustls-pemfile = "2"
 rustls-pki-types = "1.11"
+scc = "2.3.4"
 scopeguard = "1.1"
 sysinfo = "0.29.2"
 sd-notify = "0.4.1"
diff --git a/pageserver/Cargo.toml b/pageserver/Cargo.toml
index 10ec455715..0e29517afa 100644
--- a/pageserver/Cargo.toml
+++ b/pageserver/Cargo.toml
@@ -27,7 +27,6 @@ chrono = { workspace = true, features = ["serde"] }
 clap = { workspace = true, features = ["string"] }
 consumption_metrics.workspace = true
 crc32c.workspace = true
-dashmap.workspace = true
 either.workspace = true
 fail.workspace = true
 futures.workspace = true
@@ -53,6 +52,7 @@ rand.workspace = true
 range-set-blaze = { version = "0.1.16", features = ["alloc"] }
 regex.workspace = true
 rustls.workspace = true
+scc.workspace = true
 scopeguard.workspace = true
 send-future.workspace = true
 serde.workspace = true
diff --git a/pageserver/src/page_cache.rs b/pageserver/src/page_cache.rs
index 3522e17134..d64f6d3c99 100644
--- a/pageserver/src/page_cache.rs
+++ b/pageserver/src/page_cache.rs
@@ -67,8 +67,8 @@
 //! mapping is automatically removed and the slot is marked free.
 //!
 
-use dashmap::DashMap;
-use dashmap::Entry;
+use scc::HashMap;
+use scc::hash_map::Entry;
 use std::sync::atomic::{AtomicU8, AtomicU64, AtomicUsize, Ordering};
 use std::sync::{Arc, Weak};
 use std::time::Duration;
@@ -194,7 +194,7 @@ impl SlotInner {
 }
 
 pub struct PageCache {
-    immutable_page_map: std::sync::Arc::<DashMap<(FileId, u32), usize>>,
+    immutable_page_map: std::sync::Arc::<HashMap<(FileId, u32), usize>>,
 
     /// The actual buffers with their metadata.
     slots: Box<[Slot]>,
@@ -511,7 +511,7 @@ impl PageCache {
                 match self.immutable_page_map.entry((*file_id, *blkno)) {
                     Entry::Occupied(entry) => Some(*entry.get()),
                     Entry::Vacant(entry) => {
-                        entry.insert(slot_idx);
+                        entry.insert_entry(slot_idx);
                         None
                     }
                 }