feat: implement LMDB database backend

- Add nostr-lmdb dependency (v0.44) for persistent storage
- Create SharedDatabase type alias for database abstraction
- Update all database-related functions to use trait object
- Support runtime selection via NGIT_DATABASE_BACKEND env var

Database backends:
- memory: In-memory (default, fastest, no persistence)
- lmdb: LMDB backend (persistent, general purpose)

All 34 tests pass with the new implementation.

7 files changed, 289 insertions, 37 deletions

diff --git a/.env.example b/.env.example
index 0a27bbb..796415e 100644
--- a/.env.example
+++ b/.env.example
@@ -17,7 +17,7 @@ NGIT_RELAY_DATA_PATH=./data/relay
 # Database backend (memory, nostrdb, lmdb)
 # - memory: In-memory database (default, fastest, no persistence)
 # - nostrdb: NostrDB backend (persistent, optimized for Nostr) [Not yet implemented]
-# - lmdb: LMDB backend (persistent, general purpose) [Not yet implemented]
+# - lmdb: LMDB backend (persistent, general purpose)
 NGIT_DATABASE_BACKEND=memory
 
 # Server configuration
diff --git a/Cargo.lock b/Cargo.lock
index aa78542..6fcb65f 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -248,6 +248,9 @@ name = "bitflags"
 version = "2.10.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "812e12b5285cc515a9c72a5c1d3b6d46a19dac5acfef5265968c166106e31dd3"
+dependencies = [
+ "serde_core",
+]
 
 [[package]]
 name = "block-buffer"
@@ -274,6 +277,12 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "46c5e41b57b8bba42a04676d81cb89e9ee8e859a1a66f80a5a72e1cb76b34d43"
 
 [[package]]
+name = "byteorder"
+version = "1.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1fd0f2584146f6f2ef48085050886acf353beff7305ebd1ae69500e27c67f64b"
+
+[[package]]
 name = "bytes"
 version = "1.10.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -433,6 +442,21 @@ dependencies = [
 ]
 
 [[package]]
+name = "crossbeam-queue"
+version = "0.3.12"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0f58bbc28f91df819d0aa2a2c00cd19754769c2fad90579b3592b1c9ba7a3115"
+dependencies = [
+ "crossbeam-utils",
+]
+
+[[package]]
+name = "crossbeam-utils"
+version = "0.8.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d0a5c400df2834b80a4c3327b3aad3a4c4cd4de0629063962b03235697506a28"
+
+[[package]]
 name = "crypto-common"
 version = "0.1.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -478,6 +502,15 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "1aaf95b3e5c8f23aa320147307562d361db0ae0d51242340f558153b4eb2439b"
 
 [[package]]
+name = "doxygen-rs"
+version = "0.4.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "415b6ec780d34dcf624666747194393603d0373b7141eef01d12ee58881507d9"
+dependencies = [
+ "phf",
+]
+
+[[package]]
 name = "either"
 version = "1.15.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -521,6 +554,16 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "52051878f80a721bb68ebfbc930e07b65ba72f2da88968ea5c06fd6ca3d3a127"
 
 [[package]]
+name = "flatbuffers"
+version = "25.9.23"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "09b6620799e7340ebd9968d2e0708eb82cf1971e9a16821e2091b6d6e475eed5"
+dependencies = [
+ "bitflags 2.10.0",
+ "rustc_version",
+]
+
+[[package]]
 name = "flate2"
 version = "1.1.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -531,6 +574,18 @@ dependencies = [
 ]
 
 [[package]]
+name = "flume"
+version = "0.11.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "da0e4dd2a88388a1f4ccc7c9ce104604dab68d9f408dc34cd45823d5a9069095"
+dependencies = [
+ "futures-core",
+ "futures-sink",
+ "nanorand",
+ "spin",
+]
+
+[[package]]
 name = "fnv"
 version = "1.0.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -769,6 +824,40 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "2304e00983f87ffb38b55b444b5e3b60a884b5d30c0fca7d82fe33449bbe55ea"
 
 [[package]]
+name = "heed"
+version = "0.20.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7d4f449bab7320c56003d37732a917e18798e2f1709d80263face2b4f9436ddb"
+dependencies = [
+ "bitflags 2.10.0",
+ "byteorder",
+ "heed-traits",
+ "heed-types",
+ "libc",
+ "lmdb-master-sys",
+ "once_cell",
+ "page_size",
+ "synchronoise",
+ "url",
+]
+
+[[package]]
+name = "heed-traits"
+version = "0.20.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "eb3130048d404c57ce5a1ac61a903696e8fcde7e8c2991e9fcfc1f27c3ef74ff"
+
+[[package]]
+name = "heed-types"
+version = "0.20.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9d3f528b053a6d700b2734eabcd0fd49cb8230647aa72958467527b0b7917114"
+dependencies = [
+ "byteorder",
+ "heed-traits",
+]
+
+[[package]]
 name = "hex"
 version = "0.4.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -1152,6 +1241,17 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "6373607a59f0be73a39b6fe456b8192fcc3585f602af20751600e974dd455e77"
 
 [[package]]
+name = "lmdb-master-sys"
+version = "0.2.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "864808e0b19fb6dd3b70ba94ee671b82fce17554cf80aeb0a155c65bb08027df"
+dependencies = [
+ "cc",
+ "doxygen-rs",
+ "libc",
+]
+
+[[package]]
 name = "lock_api"
 version = "0.4.14"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -1215,6 +1315,15 @@ dependencies = [
 ]
 
 [[package]]
+name = "nanorand"
+version = "0.7.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6a51313c5820b0b02bd422f4b44776fbf47961755c74ce64afc73bfad10226c3"
+dependencies = [
+ "getrandom 0.2.16",
+]
+
+[[package]]
 name = "native-tls"
 version = "0.2.14"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -1250,6 +1359,7 @@ dependencies = [
  "http-body-util",
  "hyper 1.8.1",
  "hyper-util",
+ "nostr-lmdb",
  "nostr-relay-builder",
  "nostr-sdk 0.44.1",
  "serde",
@@ -1327,6 +1437,7 @@ version = "0.44.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7462c9d8ae5ef6a28d66a192d399ad2530f1f2130b13186296dbb11bdef5b3d1"
 dependencies = [
+ "flatbuffers",
  "lru",
  "nostr 0.44.1",
  "tokio",
@@ -1342,6 +1453,21 @@ dependencies = [
 ]
 
 [[package]]
+name = "nostr-lmdb"
+version = "0.44.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1201bcf1f900c352f9f2cea5249960dc6b23049b65699a516e1327243becf6a2"
+dependencies = [
+ "async-utility",
+ "flume",
+ "heed",
+ "nostr 0.44.1",
+ "nostr-database 0.44.0",
+ "tokio",
+ "tracing",
+]
+
+[[package]]
 name = "nostr-relay-builder"
 version = "0.44.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -1502,6 +1628,16 @@ dependencies = [
 ]
 
 [[package]]
+name = "page_size"
+version = "0.6.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "30d5b2194ed13191c1999ae0704b7839fb18384fa22e49b57eeaa97d79ce40da"
+dependencies = [
+ "libc",
+ "winapi",
+]
+
+[[package]]
 name = "parking_lot"
 version = "0.12.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -1552,6 +1688,48 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9b4f627cb1b25917193a259e49bdad08f671f8d9708acfd5fe0a8c1455d87220"
 
 [[package]]
+name = "phf"
+version = "0.11.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1fd6780a80ae0c52cc120a26a1a42c1ae51b247a253e4e06113d23d2c2edd078"
+dependencies = [
+ "phf_macros",
+ "phf_shared",
+]
+
+[[package]]
+name = "phf_generator"
+version = "0.11.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3c80231409c20246a13fddb31776fb942c38553c51e871f8cbd687a4cfb5843d"
+dependencies = [
+ "phf_shared",
+ "rand 0.8.5",
+]
+
+[[package]]
+name = "phf_macros"
+version = "0.11.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f84ac04429c13a7ff43785d75ad27569f2951ce0ffd30a3321230db2fc727216"
+dependencies = [
+ "phf_generator",
+ "phf_shared",
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "phf_shared"
+version = "0.11.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "67eabc2ef2a60eb7faa00097bd1ffdb5bd28e62bf39990626a582201b7a754e5"
+dependencies = [
+ "siphasher",
+]
+
+[[package]]
 name = "pin-project-lite"
 version = "0.2.16"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -1774,6 +1952,15 @@ dependencies = [
 ]
 
 [[package]]
+name = "rustc_version"
+version = "0.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cfcb3a22ef46e85b45de6ee7e79d063319ebb6594faafcf1c225ea92ab6e9b92"
+dependencies = [
+ "semver",
+]
+
+[[package]]
 name = "rustix"
 version = "1.1.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -1921,6 +2108,12 @@ dependencies = [
 ]
 
 [[package]]
+name = "semver"
+version = "1.0.27"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d767eb0aabc880b29956c35734170f26ed551a859dbd361d140cdbeca61ab1e2"
+
+[[package]]
 name = "serde"
 version = "1.0.228"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -2028,6 +2221,12 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d66dc143e6b11c1eddc06d5c423cfc97062865baf299914ab64caa38182078fe"
 
 [[package]]
+name = "siphasher"
+version = "1.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "56199f7ddabf13fe5074ce809e7d3f42b42ae711800501b5b16ea82ad029c39d"
+
+[[package]]
 name = "slab"
 version = "0.4.11"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -2060,6 +2259,15 @@ dependencies = [
 ]
 
 [[package]]
+name = "spin"
+version = "0.9.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6980e8d7511241f8acf4aebddbb1ff938df5eebe98691418c4468d0b72a96a67"
+dependencies = [
+ "lock_api",
+]
+
+[[package]]
 name = "stable_deref_trait"
 version = "1.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -2095,6 +2303,15 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "2047c6ded9c721764247e62cd3b03c09ffc529b2ba5b10ec482ae507a4a70160"
 
 [[package]]
+name = "synchronoise"
+version = "1.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3dbc01390fc626ce8d1cffe3376ded2b72a11bb70e1c75f404a210e4daa4def2"
+dependencies = [
+ "crossbeam-queue",
+]
+
+[[package]]
 name = "synstructure"
 version = "0.13.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -2625,6 +2842,28 @@ dependencies = [
 ]
 
 [[package]]
+name = "winapi"
+version = "0.3.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5c839a674fcd7a98952e593242ea400abe93992746761e38641405d28b00f419"
+dependencies = [
+ "winapi-i686-pc-windows-gnu",
+ "winapi-x86_64-pc-windows-gnu",
+]
+
+[[package]]
+name = "winapi-i686-pc-windows-gnu"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ac3b87c63620426dd9b991e5ce0329eff545bccbbb34f3be09ff6fb6ab51b7b6"
+
+[[package]]
+name = "winapi-x86_64-pc-windows-gnu"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "712e227841d057c1ee1cd2fb22fa7e5a5461ae8e48fa2ca79ec42cfc1931183f"
+
+[[package]]
 name = "windows-core"
 version = "0.62.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
diff --git a/Cargo.toml b/Cargo.toml
index 3e836f9..02c66ac 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -21,6 +21,7 @@ nostr-relay-builder = "0.44"
 
 # Nostr
 nostr-sdk = "0.44"
+nostr-lmdb = "0.44"
 
 # Utilities
 futures-util = "0.3"
diff --git a/src/git/authorization.rs b/src/git/authorization.rs
index 3b0e759..4896fc0 100644
--- a/src/git/authorization.rs
+++ b/src/git/authorization.rs
@@ -31,9 +31,9 @@ use anyhow::{anyhow, Result};
 use nostr_relay_builder::prelude::*;
 use nostr_sdk::{EventId, ToBech32};
 use std::collections::{HashMap, HashSet};
-use std::sync::Arc;
 use tracing::debug;
 
+use crate::nostr::builder::SharedDatabase;
 use crate::nostr::events::{
     RepositoryAnnouncement, RepositoryState, KIND_PR, KIND_PR_UPDATE, KIND_REPOSITORY_ANNOUNCEMENT,
     KIND_REPOSITORY_STATE,
@@ -56,7 +56,7 @@ pub struct RepositoryData {
 /// This performs a single database query to fetch both announcement and state events,
 /// which is more efficient than separate queries.
 pub async fn fetch_repository_data(
-    database: &Arc<MemoryDatabase>,
+    database: &SharedDatabase,
     identifier: &str,
 ) -> Result<RepositoryData> {
     let filter = Filter::new()
@@ -284,7 +284,7 @@ pub fn is_latest_state(
 ///
 /// Returns an `AuthorizationResult` that indicates whether a push is authorized.
 pub async fn get_authorization_from_db(
-    database: &Arc<MemoryDatabase>,
+    database: &SharedDatabase,
     identifier: &str,
 ) -> Result<AuthorizationResult> {
     // Fetch all repository data with a single query
@@ -340,7 +340,7 @@ pub async fn get_authorization_from_db(
 ///
 /// Returns an `AuthorizationResult` that indicates whether a push is authorized.
 pub async fn get_authorization_for_owner(
-    database: &Arc<MemoryDatabase>,
+    database: &SharedDatabase,
     identifier: &str,
     owner_pubkey: &str,
 ) -> Result<AuthorizationResult> {
@@ -817,7 +817,7 @@ pub fn npub_to_pubkey(npub: &str) -> Result<String> {
 /// - `Ok(None)` if the event doesn't exist (push should be allowed)
 /// - `Err(_)` on database errors
 pub async fn get_event_commit_tag(
-    database: &Arc<MemoryDatabase>,
+    database: &SharedDatabase,
     event_id: &EventId,
 ) -> Result<Option<String>> {
     // Query for PR (1618) and PR Update (1619) events with this ID
@@ -872,7 +872,7 @@ pub async fn get_event_commit_tag(
 /// * `Ok(())` if all refs/nostr/ pushes are valid
 /// * `Err(_)` if any ref has invalid event ID format or fails commit validation
 pub async fn validate_nostr_ref_pushes(
-    database: &Arc<MemoryDatabase>,
+    database: &SharedDatabase,
     pushed_refs: &[(String, String, String)],
 ) -> Result<()> {
     for (_, new_oid, ref_name) in pushed_refs {
diff --git a/src/git/handlers.rs b/src/git/handlers.rs
index e84cabb..8e5f5e1 100644
--- a/src/git/handlers.rs
+++ b/src/git/handlers.rs
@@ -4,9 +4,7 @@
 
 use http_body_util::Full;
 use hyper::{body::Bytes, Response, StatusCode};
-use nostr_relay_builder::prelude::MemoryDatabase;
 use std::path::PathBuf;
-use std::sync::Arc;
 use tokio::io::{AsyncReadExt, AsyncWriteExt};
 use tracing::{debug, error, info, warn};
 
@@ -18,6 +16,7 @@ use super::protocol::{GitService, PktLine};
 use super::subprocess::GitSubprocess;
 use super::try_set_head_if_available;
 
+use crate::nostr::builder::SharedDatabase;
 use crate::nostr::events::RepositoryState;
 
 /// Handle GET /info/refs?service=git-{upload,receive}-pack
@@ -178,7 +177,7 @@ pub async fn handle_upload_pack(
 pub async fn handle_receive_pack(
     repo_path: PathBuf,
     request_body: Bytes,
-    database: Option<Arc<MemoryDatabase>>,
+    database: Option<SharedDatabase>,
     identifier: &str,
     owner_pubkey: &str,
 ) -> Result<Response<Full<Bytes>>, GitError> {
@@ -310,7 +309,7 @@ pub async fn handle_receive_pack(
 /// 5. Validates that pushed refs match the state
 /// 6. Validates refs/nostr/<event-id> has valid event id and if event exists, `c` tag matches ref
 async fn authorize_push(
-    database: &Arc<MemoryDatabase>,
+    database: &SharedDatabase,
     identifier: &str,
     owner_pubkey: &str,
     request_body: &Bytes,
diff --git a/src/http/mod.rs b/src/http/mod.rs
index 5cf8dbe..4665281 100644
--- a/src/http/mod.rs
+++ b/src/http/mod.rs
@@ -7,7 +7,6 @@ pub mod nip11;
 use std::future::Future;
 use std::net::SocketAddr;
 use std::pin::Pin;
-use std::sync::Arc;
 
 use base64::Engine;
 use http_body_util::{BodyExt, Full};
@@ -17,7 +16,6 @@ use hyper::server::conn::http1;
 use hyper::service::Service;
 use hyper::{Method, Request, Response};
 use hyper_util::rt::TokioIo;
-use nostr_relay_builder::prelude::MemoryDatabase;
 use nostr_relay_builder::LocalRelay;
 use nostr_sdk::hashes::sha1::Hash as Sha1Hash;
 use nostr_sdk::hashes::{Hash, HashEngine};
@@ -26,6 +24,7 @@ use tokio::net::TcpListener;
 
 use crate::config::Config;
 use crate::git;
+use crate::nostr::builder::SharedDatabase;
 
 /// CORS headers required by GRASP-01 specification (lines 40-47)
 const CORS_ALLOW_ORIGIN: &str = "*";
@@ -90,7 +89,7 @@ struct HttpService {
     config: Config,
     remote: SocketAddr,
     /// Database reference for direct queries (e.g., push authorization)
-    database: Arc<MemoryDatabase>,
+    database: SharedDatabase,
 }
 
 impl HttpService {
@@ -98,7 +97,7 @@ impl HttpService {
         relay: LocalRelay,
         config: Config,
         remote: SocketAddr,
-        database: Arc<MemoryDatabase>,
+        database: SharedDatabase,
     ) -> Self {
         Self {
             relay,
@@ -423,7 +422,7 @@ fn derive_accept_key(request_key: &[u8]) -> String {
 pub async fn run_server(
     config: Config,
     relay: LocalRelay,
-    database: Arc<MemoryDatabase>,
+    database: SharedDatabase,
 ) -> anyhow::Result<()> {
     let bind_addr: SocketAddr = config.bind_address.parse()?;
 
diff --git a/src/nostr/builder.rs b/src/nostr/builder.rs
index 2f182ea..eabb38f 100644
--- a/src/nostr/builder.rs
+++ b/src/nostr/builder.rs
@@ -9,6 +9,7 @@ use std::sync::Arc;
 use nostr::nips::nip19::ToBech32;
 use nostr::prelude::{Alphabet, SingleLetterTag};
 use nostr::{EventId, Filter, Kind, PublicKey};
+use nostr_lmdb::NostrLMDB;
 use nostr_relay_builder::prelude::*;
 
 use crate::config::{Config, DatabaseBackend};
@@ -18,6 +19,9 @@ use crate::nostr::events::{
     KIND_PR_UPDATE, KIND_REPOSITORY_ANNOUNCEMENT, KIND_REPOSITORY_STATE,
 };
 
+/// Type alias for the shared database used by the relay
+pub type SharedDatabase = Arc<dyn NostrDatabase>;
+
 /// Result of aligning a repository with authorized state
 #[derive(Debug, Default)]
 struct AlignmentResult {
@@ -35,23 +39,33 @@ struct AlignmentResult {
 ///
 /// Validates all events according to GRASP-01 specification:
 /// - Repository announcements must list service in clone and relays tags
-/// - Repository state announcements must have valid structure  
+/// - Repository state announcements must have valid structure
 /// - Other events must reference accepted repositories or events
 /// - Forward references are supported (events referenced by accepted events)
 /// - Orphan events with no valid references are rejected
 ///
 /// Uses stateful database queries to check event relationships.
-#[derive(Debug, Clone)]
+#[derive(Clone)]
 pub struct Nip34WritePolicy {
     domain: String,
-    database: Arc<MemoryDatabase>,
+    database: SharedDatabase,
     git_data_path: PathBuf,
 }
 
+impl std::fmt::Debug for Nip34WritePolicy {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("Nip34WritePolicy")
+            .field("domain", &self.domain)
+            .field("git_data_path", &self.git_data_path)
+            .field("database", &"<database>")
+            .finish()
+    }
+}
+
 impl Nip34WritePolicy {
     pub fn new(
         domain: impl Into<String>,
-        database: Arc<MemoryDatabase>,
+        database: SharedDatabase,
         git_data_path: impl Into<PathBuf>,
     ) -> Self {
         Self {
@@ -104,7 +118,7 @@ impl Nip34WritePolicy {
     /// The authorized_pubkeys should be the owner and maintainers of a specific
     /// announcement, so different owners with the same identifier don't interfere.
     async fn is_latest_state_for_identifier(
-        database: &Arc<MemoryDatabase>,
+        database: &SharedDatabase,
         state: &RepositoryState,
         authorized_pubkeys: &[PublicKey],
     ) -> Result<bool, String> {
@@ -155,7 +169,7 @@ impl Nip34WritePolicy {
     /// should update HEAD in the repository of the announcement owner,
     /// not in the maintainer's own (possibly non-existent) repository.
     async fn find_authorized_announcements(
-        database: &Arc<MemoryDatabase>,
+        database: &SharedDatabase,
         identifier: &str,
         state_author: &PublicKey,
     ) -> Result<Vec<RepositoryAnnouncement>, String> {
@@ -205,7 +219,7 @@ impl Nip34WritePolicy {
     /// - This state event is the latest for the identifier in that context
     async fn identify_owner_repositories(
         &self,
-        database: &Arc<MemoryDatabase>,
+        database: &SharedDatabase,
         state: &RepositoryState,
     ) -> Result<Vec<(RepositoryAnnouncement, std::path::PathBuf)>, String> {
         // Find all announcements where state author is authorized
@@ -485,7 +499,7 @@ impl Nip34WritePolicy {
     /// Ok(Some(n)) if n refs were deleted, Ok(None) if no action taken, Err on failure
     async fn validate_pr_nostr_ref(
         &self,
-        database: &Arc<MemoryDatabase>,
+        database: &SharedDatabase,
         event: &Event,
     ) -> Result<Option<usize>, String> {
         let event_id = event.id.to_hex();
@@ -651,7 +665,7 @@ impl Nip34WritePolicy {
     /// Check if any addressable events (repositories) exist in database
     /// Returns the first matching addressable reference found, or None if none match
     async fn find_accepted_repository(
-        database: &Arc<MemoryDatabase>,
+        database: &SharedDatabase,
         addressables: &[String],
     ) -> Result<Option<String>, String> {
         if addressables.is_empty() {
@@ -724,7 +738,7 @@ impl Nip34WritePolicy {
     /// Check if any events exist in database
     /// Returns the first matching event ID found, or None if none match
     async fn find_accepted_event(
-        database: &Arc<MemoryDatabase>,
+        database: &SharedDatabase,
         event_ids: &[EventId],
     ) -> Result<Option<EventId>, String> {
         if event_ids.is_empty() {
@@ -752,7 +766,7 @@ impl Nip34WritePolicy {
     /// This optimization recognizes that replaceable events are referenced by coordinate address,
     /// while regular events are referenced by event ID.
     async fn is_referenced_by_accepted(
-        database: &Arc<MemoryDatabase>,
+        database: &SharedDatabase,
         event: &Event,
     ) -> Result<bool, String> {
         let kind_u16 = event.kind.as_u16();
@@ -1152,14 +1166,14 @@ pub struct RelayWithDatabase {
     /// The local relay instance
     pub relay: LocalRelay,
     /// The database Arc that can be used for direct queries
-    pub database: Arc<MemoryDatabase>,
+    pub database: SharedDatabase,
 }
 
 /// Create a configured LocalRelay with full GRASP-01 validation
 ///
 /// Returns a `RelayWithDatabase` struct containing:
 /// - The `LocalRelay` for handling WebSocket connections
-/// - The `Arc<MemoryDatabase>` for direct database queries (e.g., push authorization)
+/// - The `SharedDatabase` for direct database queries (e.g., push authorization)
 pub fn create_relay(config: &Config) -> Result<RelayWithDatabase> {
     tracing::info!("Configuring nostr relay with GRASP-01 validation...");
 
@@ -1167,7 +1181,7 @@ pub fn create_relay(config: &Config) -> Result<RelayWithDatabase> {
     let db_path = Path::new(&config.relay_data_path);
 
     // Create database based on configuration
-    let database = match config.database_backend {
+    let database: SharedDatabase = match config.database_backend {
         DatabaseBackend::Memory => {
             tracing::info!("Using in-memory database (no persistence)");
             Arc::new(MemoryDatabase::with_opts(MemoryDatabaseOptions {
@@ -1187,13 +1201,13 @@ pub fn create_relay(config: &Config) -> Result<RelayWithDatabase> {
         }
         DatabaseBackend::Lmdb => {
             tracing::info!("Using LMDB backend at: {}", db_path.display());
-            // TODO: Implement LMDB backend once nostr-relay-builder supports it
-            // For now, fall back to memory database
-            tracing::warn!("LMDB backend not yet implemented, using in-memory database");
-            Arc::new(MemoryDatabase::with_opts(MemoryDatabaseOptions {
-                events: true,
-                max_events: Some(100_000),
-            }))
+            // Ensure the database directory exists
+            std::fs::create_dir_all(db_path).map_err(|e| {
+                anyhow::anyhow!("Failed to create LMDB directory {}: {}", db_path.display(), e)
+            })?;
+            Arc::new(NostrLMDB::open(db_path).map_err(|e| {
+                anyhow::anyhow!("Failed to open LMDB database at {}: {}", db_path.display(), e)
+            })?)
         }
     };