From 392d447b99eb54a163e6682597dfb60a96799546 Mon Sep 17 00:00:00 2001
From: Jaco <jacogr@gmail.com>
Date: Thu, 6 Jan 2022 08:31:13 +0100
Subject: [PATCH] Adjust LRU historic size (clarify isCachable flag) (#4419)

---
 CHANGELOG.md                          | 7 +++++++
 packages/rpc-core/src/bundle.ts       | 2 ++
 packages/rpc-provider/src/lru.ts      | 5 ++++-
 packages/rpc-provider/src/ws/index.ts | 1 +
 4 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index f8115408c4..cccf0c9606 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,12 @@
 # CHANGELOG
 
+## master
+
+Changes:
+
+- Adjust max-entries in historic provider LRU
+
+
 ## 7.2.1 Jan 3, 2022
 
 Upgrade priority: Low. Recommended for users generating TS chain-specific augmentations.
diff --git a/packages/rpc-core/src/bundle.ts b/packages/rpc-core/src/bundle.ts
index e00e3dc6ee..f4688e4ccc 100644
--- a/packages/rpc-core/src/bundle.ts
+++ b/packages/rpc-core/src/bundle.ts
@@ -204,6 +204,8 @@ export class RpcCore {
         ? await this.#getBlockRegistry(u8aToU8a(blockHash))
         : { registry: this.#registryDefault };
       const params = this._formatInputs(registry, null, def, values);
+
+      // only cache .at(<blockHash>) queries, e.g. where valid blockHash was supplied
       const result = await this.provider.send<AnyJson>(rpcName, params.map((p) => p.toJSON()), !!blockHash);
 
       return this._formatResult(isScale, registry, blockHash, method, def, params, result);
diff --git a/packages/rpc-provider/src/lru.ts b/packages/rpc-provider/src/lru.ts
index 2908705996..e68448c144 100644
--- a/packages/rpc-provider/src/lru.ts
+++ b/packages/rpc-provider/src/lru.ts
@@ -1,7 +1,10 @@
 // Copyright 2017-2022 @polkadot/rpc-provider authors & contributors
 // SPDX-License-Identifier: Apache-2.0
 
-const DEFAULT_CAPACITY = 2048;
+// Assuming all 1.5MB responses, we apply a default allowing for 576MB
+// cache space (depending on the historic queries this would vary, metadata
+// for Kusama/Polkadot/Substrate falls between 600-750K, 2x for estimate)
+const DEFAULT_CAPACITY = 384;
 
 class LRUNode {
   public readonly key: string;
diff --git a/packages/rpc-provider/src/ws/index.ts b/packages/rpc-provider/src/ws/index.ts
index 5834f65901..a1e1e59431 100644
--- a/packages/rpc-provider/src/ws/index.ts
+++ b/packages/rpc-provider/src/ws/index.ts
@@ -328,6 +328,7 @@ export class WsProvider implements ProviderInterface {
    * ```
    */
   public subscribe (type: string, method: string, params: unknown[], callback: ProviderInterfaceCallback): Promise<number | string> {
+    // subscriptions are not cached, LRU applies to .at(<blockHash>) only
     return this.send<number | string>(method, params, false, { callback, type });
   }