Use rustc' FxHasher instead of the std one

Author: sandhose

Cargo.lock

@@ -25,6 +25,7 @@ compact_str.workspace = true
 tracing.workspace = true
 tracing-indicatif.workspace = true
 futures-util = "0.3.30"
+rustc-hash = "2.1.1"
 
 rand.workspace = true
 uuid = "1.13.1"

crates/syn2mas/Cargo.toml

@@ -9,6 +9,9 @@ mod synapse_reader;
 mod migration;
 mod progress_stream;
 
+type RandomState = rustc_hash::FxBuildHasher;
+type HashMap<K, V> = rustc_hash::FxHashMap<K, V>;
+
 pub use self::{
     mas_writer::{checks::mas_pre_migration_checks, locking::LockedMasDatabase, MasWriter},
     migration::migrate,

crates/syn2mas/src/lib.rs

@@ -16,7 +16,7 @@
 //! This module does not implement any of the safety checks that should be run
 //! *before* the migration.
 
-use std::{collections::HashMap, pin::pin, time::Instant};
+use std::{pin::pin, time::Instant};
 
 use chrono::{DateTime, Utc};
 use compact_str::CompactString;
@@ -41,7 +41,7 @@ use crate::{
         self, ExtractLocalpartError, FullUserId, SynapseAccessToken, SynapseDevice,
         SynapseExternalId, SynapseRefreshableTokenPair, SynapseThreepid, SynapseUser,
     },
-    SynapseReader,
+    HashMap, RandomState, SynapseReader,
 };
 
 #[derive(Debug, Error, ContextInto)]
@@ -114,7 +114,7 @@ struct MigrationState {
 
     /// A mapping of Synapse external ID providers to MAS upstream OAuth 2.0
     /// provider ID
-    provider_id_mapping: HashMap<String, Uuid>,
+    provider_id_mapping: std::collections::HashMap<String, Uuid>,
 }
 
 /// Performs a migration from Synapse's database to MAS' database.
@@ -137,7 +137,7 @@ pub async fn migrate(
     server_name: String,
     clock: &dyn Clock,
     rng: &mut impl RngCore,
-    provider_id_mapping: HashMap<String, Uuid>,
+    provider_id_mapping: std::collections::HashMap<String, Uuid>,
 ) -> Result<(), Error> {
     let span = Span::current();
     span.pb_set_message("counting work");
@@ -148,8 +148,11 @@ pub async fn migrate(
         server_name,
         // We oversize the hashmaps, as the estimates are innaccurate, and we would like to avoid
         // reallocations.
-        users: HashMap::with_capacity(counts.users * 9 / 8),
-        devices_to_compat_sessions: HashMap::with_capacity(counts.devices * 9 / 8),
+        users: HashMap::with_capacity_and_hasher(counts.users * 9 / 8, RandomState::default()),
+        devices_to_compat_sessions: HashMap::with_capacity_and_hasher(
+            counts.devices * 9 / 8,
+            RandomState::default(),
+        ),
         provider_id_mapping,
     };