RPC: add caching to getLargestAccounts (#15154) (#15271)

* introduce get largest accounts cache

* remove cache size and change hash key

* remove eq and hash derivation from commitment config

* add slot to the cache

(cherry picked from commit 4013f91dbe)

Co-authored-by: Josh <josh.hundley@gmail.com>

core/src/rpc_service.rs

@@ -16,6 +16,7 @@ use jsonrpc_http_server::{
     RequestMiddlewareAction, ServerBuilder,
 };
 use regex::Regex;
+use solana_client::rpc_cache::LargestAccountsCache;
 use solana_ledger::blockstore::Blockstore;
 use solana_metrics::inc_new_counter_info;
 use solana_runtime::{
@@ -34,6 +35,8 @@ use std::{
 };
 use tokio::runtime;
 
+const LARGEST_ACCOUNTS_CACHE_DURATION: u64 = 60 * 60 * 2;
+
 pub struct JsonRpcService {
     thread_hdl: JoinHandle<()>,
 
@@ -282,6 +285,10 @@ impl JsonRpcService {
             override_health_check,
         ));
 
+        let largest_accounts_cache = Arc::new(RwLock::new(LargestAccountsCache::new(
+            LARGEST_ACCOUNTS_CACHE_DURATION,
+        )));
+
         let tpu_address = cluster_info.my_contact_info().tpu;
         let mut runtime = runtime::Builder::new()
             .threaded_scheduler()
@@ -341,6 +348,7 @@ impl JsonRpcService {
             &runtime,
             bigtable_ledger_storage,
             optimistically_confirmed_bank,
+            largest_accounts_cache,
         );
 
         let leader_info =