added Cassandra caches to the llm_caching notebook doc (#10889)

This adds a section on usage of `CassandraCache` and
`CassandraSemanticCache` to the doc notebook about caching LLMs, as
suggested in [this
comment](https://github.com/langchain-ai/langchain/pull/9772/#issuecomment-1710544100)
on a previous merged PR.

I also spotted what looks like a mismatch between different executions
and propose a fix (line 98).

Being the result of several runs, the cell execution numbers are
scrambled somewhat, so I volunteer to refine this PR by (manually)
re-numbering the cells to restore the appearance of a single, smooth
running (for the sake of orderly execution :)

docs/extras/integrations/llms/llm_caching.ipynb

@@ -95,7 +95,7 @@
     {
      "data": {
       "text/plain": [
-       "'\\n\\nWhy did the chicken cross the road?\\n\\nTo get to the other side.'"
+       "\"\\n\\nWhy couldn't the bicycle stand up by itself? It was...two tired!\""
       ]
      },
      "execution_count": 7,
@@ -811,6 +811,228 @@
     "langchain.llm_cache = SQLAlchemyCache(engine, FulltextLLMCache)"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "id": "eeba7d60",
+   "metadata": {},
+   "source": [
+    "## `Cassandra` caches\n",
+    "\n",
+    "You can use Cassandra / Astra DB for caching LLM responses, choosing from the exact-match `CassandraCache` or the (vector-similarity-based) `CassandraSemanticCache`.\n",
+    "\n",
+    "Let's see both in action in the following cells."
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "a4a6725d",
+   "metadata": {},
+   "source": [
+    "#### Connect to the DB\n",
+    "\n",
+    "First you need to establish a `Session` to the DB and to specify a _keyspace_ for the cache table(s). The following gets you started with an Astra DB instance (see e.g. [here](https://cassio.org/start_here/#vector-database) for more backends and connection options)."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 1,
+   "id": "cc53ce1b",
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "\n",
+      "Keyspace name? my_keyspace\n",
+      "\n",
+      "Astra DB Token (\"AstraCS:...\") ········\n",
+      "Full path to your Secure Connect Bundle? /path/to/secure-connect-databasename.zip\n"
+     ]
+    }
+   ],
+   "source": [
+    "import getpass\n",
+    "\n",
+    "keyspace = input(\"\\nKeyspace name? \")\n",
+    "ASTRA_DB_APPLICATION_TOKEN = getpass.getpass('\\nAstra DB Token (\"AstraCS:...\") ')\n",
+    "ASTRA_DB_SECURE_BUNDLE_PATH = input(\"Full path to your Secure Connect Bundle? \")"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 2,
+   "id": "4617f485",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "from cassandra.cluster import Cluster\n",
+    "from cassandra.auth import PlainTextAuthProvider\n",
+    "\n",
+    "cluster = Cluster(\n",
+    "    cloud={\n",
+    "        \"secure_connect_bundle\": ASTRA_DB_SECURE_BUNDLE_PATH,\n",
+    "    },\n",
+    "    auth_provider=PlainTextAuthProvider(\"token\", ASTRA_DB_APPLICATION_TOKEN),\n",
+    ")\n",
+    "session = cluster.connect()"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "8665664a",
+   "metadata": {},
+   "source": [
+    "### Exact cache\n",
+    "\n",
+    "This will avoid invoking the LLM when the supplied prompt is _exactly_ the same as one encountered already:"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 6,
+   "id": "00a5e66f",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "import langchain\n",
+    "from langchain.cache import CassandraCache\n",
+    "\n",
+    "langchain.llm_cache = CassandraCache(session=session, keyspace=keyspace)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 11,
+   "id": "956a5145",
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "\n",
+      "\n",
+      "The Moon always shows the same side because it is tidally locked to Earth.\n",
+      "CPU times: user 41.7 ms, sys: 153 µs, total: 41.8 ms\n",
+      "Wall time: 1.96 s\n"
+     ]
+    }
+   ],
+   "source": [
+    "%%time\n",
+    "\n",
+    "print(llm(\"Why is the Moon always showing the same side?\"))"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 12,
+   "id": "158f0151",
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "\n",
+      "\n",
+      "The Moon always shows the same side because it is tidally locked to Earth.\n",
+      "CPU times: user 4.09 ms, sys: 0 ns, total: 4.09 ms\n",
+      "Wall time: 119 ms\n"
+     ]
+    }
+   ],
+   "source": [
+    "%%time\n",
+    "\n",
+    "print(llm(\"Why is the Moon always showing the same side?\"))"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "8fc4d017",
+   "metadata": {},
+   "source": [
+    "### Semantic cache\n",
+    "\n",
+    "This cache will do a semantic similarity search and return a hit if it finds a cached entry that is similar enough, For this, you need to provide an `Embeddings` instance of your choice."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 13,
+   "id": "b9ad3f54",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "from langchain.embeddings import OpenAIEmbeddings\n",
+    "\n",
+    "embedding=OpenAIEmbeddings()"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 14,
+   "id": "4623f95e",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "from langchain.cache import CassandraSemanticCache\n",
+    "\n",
+    "langchain.llm_cache = CassandraSemanticCache(\n",
+    "    session=session, keyspace=keyspace, embedding=embedding, table_name=\"cass_sem_cache\"\n",
+    ")"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 15,
+   "id": "1a8e577b",
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "\n",
+      "\n",
+      "The Moon always shows the same side because it is tidally locked with Earth. This means that the same side of the Moon always faces Earth.\n",
+      "CPU times: user 21.3 ms, sys: 177 µs, total: 21.4 ms\n",
+      "Wall time: 3.09 s\n"
+     ]
+    }
+   ],
+   "source": [
+    "%%time\n",
+    "\n",
+    "print(llm(\"Why is the Moon always showing the same side?\"))"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 16,
+   "id": "f7abddfd",
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "\n",
+      "\n",
+      "The Moon always shows the same side because it is tidally locked with Earth. This means that the same side of the Moon always faces Earth.\n",
+      "CPU times: user 10.9 ms, sys: 17 µs, total: 10.9 ms\n",
+      "Wall time: 461 ms\n"
+     ]
+    }
+   ],
+   "source": [
+    "%%time\n",
+    "\n",
+    "print(llm(\"How come we always see one face of the moon?\"))"
+   ]
+  },
   {
    "cell_type": "markdown",
    "id": "0c69d84d",