{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Transakcije v MariaDB/MySQL (transakcija B)\n",
    "\n",
    "### Pomožni elementi"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "# pyODBC\n",
    "import pyodbc\n",
    "try:\n",
    "    cn2.close()\n",
    "except:\n",
    "    pass\n",
    "\n",
    "# MariaDB/MySQL\n",
    "conn = \"DRIVER={MySQL ODBC 5.3 Unicode Driver};SERVER=localhost;DATABASE=sandbox;UID=tup;PWD=tupvaje\"\n",
    "cn2 = pyodbc.connect(conn, autocommit=False)\n",
    "c2=cn2.cursor()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "# Izpis rezultatov poizvedbe (pomožna funkcija)\n",
    "def tabela(rez):\n",
    "  try:\n",
    "    # Glava\n",
    "    for g in rez.description:\n",
    "        print(g[0],end=\"\\t\")\n",
    "    print(\"\\n\"+\"-\"*31)\n",
    "    # Vsebina\n",
    "    for r in rez.fetchall():\n",
    "        for a in r:\n",
    "            print(a,end=\"\\t\")\n",
    "        print()    \n",
    "    # Število vrstic\n",
    "    print(\"Vseh vrstic je\", rez.rowcount)\n",
    "  except Exception(e):\n",
    "    pass"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Nadaljuj s korakom A1"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Korak B1: nastavi transakcijske parametre za vse nadaljnje nove transakcije"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "# Timeout ob predolgem zaklepanju\n",
    "c2.execute(\"SET SESSION innodb_lock_wait_timeout = 5\") # Čas v sekundah\n",
    "# Preizkusite različne stopnje izolacije\n",
    "c2.execute(\"SET SESSION TRANSACTION ISOLATION LEVEL READ UNCOMMITTED\") \n",
    "# Začnemo novo transakcijo\n",
    "c2.commit()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "----\n",
    "# <font color='green'>Branje neobstoječega podatka (dirty read)</font>\n",
    "- stopnja izolacije transakcije B mora biti vsaj `READ COMMITTED`"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Korak B2: izpis vsebine tabele pred spremembo"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "c2.execute(\"SELECT * FROM jadralec\")\n",
    "tabela(c2)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Nadaljuj s korakom A4"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Korak B3: izpis vsebine tabele po spremembi v prvi povezavi"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "tabela(c2.execute(\"SELECT * FROM jadralec\"))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "collapsed": true
   },
   "source": [
    "## Korak B3: izpis vsebine tabele po razveljavitvi spremembe v prvi povezavi"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "tabela(c2.execute(\"SELECT * FROM jadralec\"))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Pri `READ UNCOMMITED` so vidne tudi nepotrjene spremembe, pri višjih stopnjah izolacije pa ne.\n",
    "\n",
    "-------------------"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# <font color='green'>Izgubljeno ažuriranje</font>"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Korak B4: začetek nove transakcije in izpis ratinga"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "1\n"
     ]
    }
   ],
   "source": [
    "c2.rollback()\n",
    "c2.execute(\"\"\" SELECT rating  \n",
    "               FROM jadralec\n",
    "               WHERE jid = 29\"\"\")\n",
    "rating = c2.fetchone()[0]\n",
    "print (rating)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Nadaljuj s korakom A8"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Korak B5: sprememba ratinga"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "ename": "Error",
     "evalue": "('HY000', '[HY000] [MySQL][ODBC 5.3(w) Driver][mysqld-5.5.5-10.1.14-MariaDB]Lock wait timeout exceeded; try restarting transaction (1205) (SQLExecDirectW)')",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mError\u001b[0m                                     Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-5-780647f29973>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m()\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0mc2\u001b[0m\u001b[1;33m.\u001b[0m\u001b[0mexecute\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;34m\"UPDATE jadralec              SET rating = ?              WHERE jid = 29\"\u001b[0m\u001b[1;33m,\u001b[0m \u001b[0mrating\u001b[0m \u001b[1;33m+\u001b[0m \u001b[1;36m10\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;31mError\u001b[0m: ('HY000', '[HY000] [MySQL][ODBC 5.3(w) Driver][mysqld-5.5.5-10.1.14-MariaDB]Lock wait timeout exceeded; try restarting transaction (1205) (SQLExecDirectW)')"
     ]
    }
   ],
   "source": [
    "c2.execute(\"UPDATE jadralec  \\\n",
    "            SET rating = ?  \\\n",
    "            WHERE jid = 29\", rating + 10)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Ne glede na stopnjo izolacije dobimo obvestilo:\n",
    " `Lock wait timeout exceeded; try restarting transaction (1205) `\n",
    "\n",
    "(razen če namesto privzetega InnoDB/XtraDB uporabimo netransakcijski shranjevalni pogon MyISAM/ARIA)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Nadaljujemo lahko le z MyISAM"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "collapsed": true
   },
   "source": [
    "## Korak B6: potrditev sprememb in izpis"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "c2.commit()\n",
    "tabela(c2.execute(\"SELECT * FROM jadralec\"))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "collapsed": true
   },
   "source": [
    "---------\n",
    "# <font color='green'>Neponovljivo branje (`non-repeatable read`)<font>\n",
    "## Potrebujemo najmanj `REPEATABLE READ` v transakciji A"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Korak B7: začetek transakcije, sprememba in potrditev"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "c2.commit()\n",
    "c2.execute(\"UPDATE jadralec  \\\n",
    "            SET rating = ?  \\\n",
    "            WHERE jid = 29\", 666)\n",
    "c2.commit()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Nadaljuj s korakom A11"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "collapsed": true
   },
   "source": [
    "---------\n",
    "# <font color='green'>Fantomsko branje (`phantom read`)<font>\n",
    "## Potrebujemo `SERIALIZABLE` v transakciji A"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Korak B8: začetek transakcije, sprememba in potrditev"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "c2.commit()\n",
    "c2.execute(\"INSERT INTO jadralec VALUES(25,'PHANTOM',42, 666)\")\n",
    "c2.commit()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Pri `SERIALIZABLE` pride do time-outa, sicer do fantomske vrstice"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Nadaljuj s korakom A13"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "c2.commit()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "----\n",
    "# <font color='green'>Mrtva zanka<font>"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Korak B9: prva sprememba in zaklepanje"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "c2.commit()\n",
    "c2.execute(\"UPDATE jadralec  \\\n",
    "            SET rating = ?  \\\n",
    "            WHERE jid = 29\", 229)\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Nadaljuj s korakom A15\n",
    "## Korak B10: druga sprememba in zaklepanje"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "c2.execute(\"UPDATE jadralec  \\\n",
    "            SET rating = ?  \\\n",
    "            WHERE jid = 22\", 222)\n",
    "c2.commit()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Pride do pojava mrtve zanke, zato se transakcija prekine in razveljavi.\n",
    "## Nadaljuj s korakom A16.\n",
    "### Za ponovitev ponovno izvršimo koraka B9 in B10."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": []
  }
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