libsql-server: use LRU cache to store active namespaces

This is a port of Marin's libsql/sqld#689

This PR replaces the namespace store dumb hashmap with an LRU cache to bound
the maximum number of namespaces loaded into memory while unbounding the number
of namespaces allocated on a sqld instance.  Additionally, this enables fully
concurrent access to namespaces by removing the global lock on the namespace
store.

Co-authored-by: Piotr Sarna <[email protected]>

Author: Marin Postma

libsql-server/Cargo.toml

@@ -76,6 +76,7 @@ tracing-subscriber = { version = "0.3.16", features = ["env-filter"] }
 http-body = "0.4"
 url = { version = "2.3", features = ["serde"] }
 uuid = { version = "1.3", features = ["v4", "serde"] }
+moka = { version = "0.12.1", features = ["future"] }
 
 [dev-dependencies]
 arbitrary = { version = "1.3.0", features = ["derive_arbitrary"] }

libsql-server/src/error.rs

@@ -92,6 +92,9 @@ pub enum Error {
     UrlParseError(#[from] url::ParseError),
     #[error("Namespace store has shutdown")]
     NamespaceStoreShutdown,
+    // This is for errors returned by moka
+    #[error(transparent)]
+    Ref(#[from] std::sync::Arc<Self>),
 }
 
 trait ResponseError: std::error::Error {
@@ -105,6 +108,12 @@ trait ResponseError: std::error::Error {
 impl ResponseError for Error {}
 
 impl IntoResponse for Error {
+    fn into_response(self) -> axum::response::Response {
+        (&self).into_response()
+    }
+}
+
+impl IntoResponse for &Error {
     fn into_response(self) -> axum::response::Response {
         use Error::*;
 
@@ -150,6 +159,7 @@ impl IntoResponse for Error {
             PrimaryStreamInterupted => self.format_err(StatusCode::INTERNAL_SERVER_ERROR),
             UrlParseError(_) => self.format_err(StatusCode::BAD_REQUEST),
             NamespaceStoreShutdown => self.format_err(StatusCode::SERVICE_UNAVAILABLE),
+            Ref(this) => this.as_ref().into_response(),
         }
     }
 }
@@ -224,7 +234,7 @@ pub enum LoadDumpError {
 
 impl ResponseError for LoadDumpError {}
 
-impl IntoResponse for LoadDumpError {
+impl IntoResponse for &LoadDumpError {
     fn into_response(self) -> axum::response::Response {
         use LoadDumpError::*;
 
@@ -244,7 +254,7 @@ impl IntoResponse for LoadDumpError {
 
 impl ResponseError for ForkError {}
 
-impl IntoResponse for ForkError {
+impl IntoResponse for &ForkError {
     fn into_response(self) -> axum::response::Response {
         match self {
             ForkError::Internal(_)