Add Redis cache implementation (langchain-ai#397)

I'm using a hash function for the key just to make sure its length
doesn't get out of hand, otherwise the implementation is quite similar.

docs/examples/prompts/llm_caching.ipynb

@@ -60,8 +60,8 @@
      "name": "stdout",
      "output_type": "stream",
      "text": [
-      "CPU times: user 30 ms, sys: 10.8 ms, total: 40.8 ms\n",
-      "Wall time: 983 ms\n"
+      "CPU times: user 30.6 ms, sys: 9.95 ms, total: 40.5 ms\n",
+      "Wall time: 730 ms\n"
      ]
     },
     {
@@ -91,8 +91,8 @@
      "name": "stdout",
      "output_type": "stream",
      "text": [
-      "CPU times: user 65 µs, sys: 1 µs, total: 66 µs\n",
-      "Wall time: 70.1 µs\n"
+      "CPU times: user 71 µs, sys: 3 µs, total: 74 µs\n",
+      "Wall time: 78.9 µs\n"
      ]
     },
     {
@@ -142,8 +142,8 @@
      "name": "stdout",
      "output_type": "stream",
      "text": [
-      "CPU times: user 6.76 ms, sys: 2.6 ms, total: 9.36 ms\n",
-      "Wall time: 7.86 ms\n"
+      "CPU times: user 5.27 ms, sys: 2.36 ms, total: 7.63 ms\n",
+      "Wall time: 6.68 ms\n"
      ]
     },
     {
@@ -167,14 +167,16 @@
    "cell_type": "code",
    "execution_count": 8,
    "id": "5bf2f6fd",
-   "metadata": {},
+   "metadata": {
+    "scrolled": true
+   },
    "outputs": [
     {
      "name": "stdout",
      "output_type": "stream",
      "text": [
-      "CPU times: user 2.52 ms, sys: 1.47 ms, total: 3.99 ms\n",
-      "Wall time: 2.98 ms\n"
+      "CPU times: user 3.05 ms, sys: 1.1 ms, total: 4.16 ms\n",
+      "Wall time: 5.58 ms\n"
      ]
     },
     {
@@ -194,6 +196,90 @@
     "llm(\"Tell me a joke\")"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "id": "278ad7ae",
+   "metadata": {},
+   "source": [
+    "### Redis Cache"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 9,
+   "id": "39f6eb0b",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "# We can do the same thing with a Redis cache\n",
+    "# (make sure your local Redis instance is running first before running this example)\n",
+    "from redis import Redis\n",
+    "from langchain.cache import RedisCache\n",
+    "langchain.llm_cache = RedisCache(redis_=Redis())"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 10,
+   "id": "28920749",
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "CPU times: user 6.75 ms, sys: 3.14 ms, total: 9.89 ms\n",
+      "Wall time: 716 ms\n"
+     ]
+    },
+    {
+     "data": {
+      "text/plain": [
+       "'\\n\\nWhy did the chicken cross the road?\\n\\nTo get to the other side!'"
+      ]
+     },
+     "execution_count": 10,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "%%time\n",
+    "# The first time, it is not yet in cache, so it should take longer\n",
+    "llm(\"Tell me a joke\")"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 11,
+   "id": "94bf9415",
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "CPU times: user 1.66 ms, sys: 1.92 ms, total: 3.57 ms\n",
+      "Wall time: 7.56 ms\n"
+     ]
+    },
+    {
+     "data": {
+      "text/plain": [
+       "'\\n\\nWhy did the chicken cross the road?\\n\\nTo get to the other side!'"
+      ]
+     },
+     "execution_count": 11,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "%%time\n",
+    "# The second time it is, so it goes faster\n",
+    "llm(\"Tell me a joke\")"
+   ]
+  },
   {
    "cell_type": "markdown",
    "id": "934943dc",
@@ -459,7 +545,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.10.8"
+   "version": "3.10.4"
   }
  },
  "nbformat": 4,

langchain/cache.py

@@ -1,6 +1,6 @@
 """Beta Feature: base interface for cache."""
 from abc import ABC, abstractmethod
-from typing import Dict, List, Optional, Tuple
+from typing import Any, Dict, List, Optional, Tuple
 
 from sqlalchemy import Column, Integer, String, create_engine, select
 from sqlalchemy.engine.base import Engine
@@ -94,3 +94,43 @@ def __init__(self, database_path: str = ".langchain.db"):
         """Initialize by creating the engine and all tables."""
         engine = create_engine(f"sqlite:///{database_path}")
         super().__init__(engine)
+
+
+class RedisCache(BaseCache):
+    """Cache that uses Redis as a backend."""
+
+    def __init__(self, redis_: Any):
+        """Initialize by passing in Redis instance."""
+        try:
+            from redis import Redis
+        except ImportError:
+            raise ValueError(
+                "Could not import redis python package. "
+                "Please install it with `pip install redis`."
+            )
+        if not isinstance(redis_, Redis):
+            raise ValueError("Please pass in Redis object.")
+        self.redis = redis_
+
+    def _key(self, prompt: str, llm_string: str, idx: int) -> str:
+        """Compute key from prompt, llm_string, and idx."""
+        return str(hash(prompt + llm_string)) + "_" + str(idx)
+
+    def lookup(self, prompt: str, llm_string: str) -> Optional[RETURN_VAL_TYPE]:
+        """Look up based on prompt and llm_string."""
+        idx = 0
+        generations = []
+        while self.redis.get(self._key(prompt, llm_string, idx)):
+            result = self.redis.get(self._key(prompt, llm_string, idx))
+            if not result:
+                break
+            elif isinstance(result, bytes):
+                result = result.decode()
+            generations.append(Generation(text=result))
+            idx += 1
+        return generations if generations else None
+
+    def update(self, prompt: str, llm_string: str, return_val: RETURN_VAL_TYPE) -> None:
+        """Update cache based on prompt and llm_string."""
+        for i, generation in enumerate(return_val):
+            self.redis.set(self._key(prompt, llm_string, i), generation.text)