issue_1262.ipynb

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   "execution_count": 1,
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   "source": [
    "import numpy as np\n",
    "import os"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
    "collapsed": true
   },
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   "source": [
    "fd = os.open('/tmp/block', os.O_RDWR|os.O_CREAT)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
   "outputs": [],
   "source": [
    "# allocate 60 G of file initialized to 0\n",
    "# 60 G should be larger than the amount of RAM but smaller than the available disk space on /tmp\n",
    "os.ftruncate(fd, 60 * (1<<30))"
   ]
  },
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   "cell_type": "code",
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   "metadata": {},
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     "name": "stdout",
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     "text": [
      "-rwxr-xr-x. 1 matthijs users 64424509440 Jun 24 22:25 /tmp/block\r\n"
     ]
    }
   ],
   "source": [
    "! ls -la /tmp/block"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {},
   "outputs": [],
   "source": [
    "m = np.memmap('/tmp/block', mode='r+')"
   ]
  },
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   "cell_type": "code",
   "execution_count": 12,
   "metadata": {},
   "outputs": [
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     "data": {
      "text/plain": [
       "64424509440"
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     "execution_count": 12,
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   "source": [
    "m.size"
   ]
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  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "memmap([0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,\n",
       "        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,\n",
       "        0, 0, 0, 0, 0, 0], dtype=uint8)"
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     "execution_count": 13,
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   "source": [
    "m[:50]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "step = 1 << 20"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "47565504512 / 64424509440\r"
     ]
    }
   ],
   "source": [
    "for i in range(0, m.size, step): \n",
    "    print(f'{i} / {m.size}', end='\\r', flush=True)\n",
    "    m[i:i+step] = 123"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
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   "source": []
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