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   "cell_type": "markdown",
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    "<style>\n",
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   "source": [
    "# Caching\n",
    "\n",
    "Vaex can cache task results, such as aggregations, or the internal hashmaps used for `groupby` operations to make recurring calculations much faster, at the cost of calculating cache keys and storing/retrieving the cached values.\n",
    "\n",
    "Internally, Vaex calculates fingerprints (e.g. hashes of data, or file paths and mtimes) to create cache keys that are similar across processes, so that a restart of a process will most likely result in similar hash keys.\n",
    "\n",
    "[See configuration of the cache.](../conf.md#cache)\n",
    "\n",
    "Caches can be turned on globally like this:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "import vaex\n",
    "df = vaex.datasets.titanic()\n",
    "vaex.cache.memory();  # cache on globally"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "One can verify that the cache is turned on via:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "True"
      ]
     },
     "execution_count": 2,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "vaex.cache.is_on()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "The cache can be globally turned off again:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "False"
      ]
     },
     "execution_count": 3,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "vaex.cache.off()\n",
    "vaex.cache.is_on()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "The cache can also be turned on with a context manager, after which it will be turned off again. Here we use a disk cache. Disk cache is shared among processes, and is ideal for processes that restart, or when using Vaex in a web service with multiple workers. Consider the following example:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [
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     "name": "stdout",
     "output_type": "stream",
     "text": [
      "29.8811345124283\n"
     ]
    }
   ],
   "source": [
    "with vaex.cache.disk(clear=True):\n",
    "    print(df.age.mean())  # The very first time the mean is computed"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [
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     "execution_count": 5,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# outside of the context manager, the cache is still off\n",
    "vaex.cache.is_on()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {},
   "outputs": [
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     "name": "stdout",
     "output_type": "stream",
     "text": [
      "29.8811345124283\n"
     ]
    }
   ],
   "source": [
    "with vaex.cache.disk():\n",
    "    print(df.age.mean())  # The second time the result is read from the cache"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "False"
      ]
     },
     "execution_count": 7,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "vaex.cache.is_on()"
   ]
  }
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