Update CACHING.md

architecture/CACHING.md

@@ -34,7 +34,7 @@ package provides two different middlewares:
 
 ## What requests are cached?
 
-As of now we have 3 different groups of cacheable EVM methods:
+As of now we have 4 different groups of cacheable EVM methods:
 - cacheable by block number (for ex.: `eth_getBlockByNumber`)
 - cacheable by block hash (for ex.: `eth_getBlockByHash`)
 - static methods (for ex.: `eth_chainId`, `net_version`)
@@ -95,6 +95,40 @@ Cacheable by tx hash means that for specific:
 - tx hash (which is part of params)
 response won't change over time, so we can cache it indefinitely
 
+`NOTE`: we can't cache txs which is in mempool, because response for same tx in mempool and in block is different:
+
+tx in mempool example:
+```json
+{
+  "jsonrpc": "2.0",
+  "id": 1,
+  "result": {
+    "blockHash": null,
+    "blockNumber": null,
+    "transactionIndex": null,
+    "from": "0x57852ef74abc9f0da78b49d16604bbf2d81c559e",
+    "gas": "0x5208",
+    ...
+  }
+}
+```
+
+tx in block example
+```json
+{
+  "jsonrpc": "2.0",
+  "id": 1,
+  "result": {
+    "blockHash": "0xcc62755636e265e1f40cc0ea757477a79a233b6a417e3a8813be2ffe6859c0aa",
+    "blockNumber": "0x7e8e5e",
+    "transactionIndex": "0x0",
+    "from": "0x57852ef74abc9f0da78b49d16604bbf2d81c559e",
+    "gas": "0x5208",
+    ...
+  }
+}
+```
+
 ### Where to find list of methods for every group?
 
 It can be found in source code: https://github.com/Kava-Labs/kava-proxy-service/blob/main/decode/evm_rpc.go