improvement: pdu cache, /sync cache

src/database.rs

@@ -17,6 +17,7 @@ use crate::{utils, Error, Result};
 use abstraction::DatabaseEngine;
 use directories::ProjectDirs;
 use log::error;
+use lru_cache::LruCache;
 use rocket::futures::{channel::mpsc, stream::FuturesUnordered, StreamExt};
 use ruma::{DeviceId, ServerName, UserId};
 use serde::Deserialize;
@@ -189,6 +190,7 @@ impl Database {
 
                 eventid_outlierpdu: builder.open_tree("eventid_outlierpdu")?,
                 prevevent_parent: builder.open_tree("prevevent_parent")?,
+                pdu_cache: RwLock::new(LruCache::new(1_000_000)),
             },
             account_data: account_data::AccountData {
                 roomuserdataid_accountdata: builder.open_tree("roomuserdataid_accountdata")?,