SQLCache.py 7.07 KB
Newer Older
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204
"""
SQL (MySQL) based cache plugin.
"""

from BaseCache import *
import time, base64

try:
  import cPickle as pickle
except ImportError:
  import pickle
    
try:
  import MySQLdb
except ImportError:
  raise CachedMethodError, "MySQLdb module is not available"

class SQLCache(BaseCache):
  """ SQL based cache plugin. """
    
  cache_expire_check_interval = 3600
    
  create_table_sql = '''CREATE TABLE %s(cache_id VARCHAR(970) NOT NULL, 
                                         value LONGTEXT,
                                         scope VARCHAR(20),
                                         stored_at INT,
                                         cache_duration INT DEFAULT 0,
                                         calculation_time FLOAT,
                                         UNIQUE(cache_id, scope))
                      '''

  insert_key_sql = '''INSERT INTO %s (cache_id, value, scope, stored_at, cache_duration, calculation_time) 
                              VALUES("%s", "%s", "%s", %s, %s, %s)
                    '''
                            
  has_key_sql = '''SELECT count(*)
                    FROM %s
                    WHERE cache_id = "%s" and scope="%s"
                    '''
                      
  get_key_sql = '''SELECT value, cache_duration, calculation_time 
                    FROM %s
                    WHERE cache_id = "%s" and scope="%s"
                    '''
                            
  delete_key_sql = '''DELETE
                       FROM %s
                       WHERE cache_id = "%s" and scope="%s"
                    '''
    
  delete_all_keys_sql = '''DELETE 
                            FROM %s
                         '''
    
  delete_all_keys_for_scope_sql = '''DELETE 
                                      FROM %s 
                                      WHERE scope="%s"
                                    '''
        
  delete_expired_keys_sql = '''DELETE 
                                FROM %s
                                WHERE cache_duration + stored_at < %s and cache_duration!=0
                              '''
  
  get_scope_list_sql = '''SELECT scope 
                           FROM %s 
                           GROUP BY scope
                        '''
                           
  get_scope_key_list_sql = '''SELECT cache_id 
                                FROM %s 
                                WHERE scope="%s"
                            '''

  def __init__(self, params):
    BaseCache.__init__(self)
    self._dbConn = None
    self._db_server = params.get('server', '')
    self._db_user = params.get('user', '')
    self._db_passwd = params.get('passwd', '')
    self._db_name = params.get('db', '')
    self._db_cache_table_name = params.get('cache_table_name')
    
    ## since SQL cache is persistent check for expired objects
    #self.expireOldCacheEntries(forceCheck=True)
    
  def getCacheStorage(self):
    """ 
    Return current DB connection or create a new one.
    See http://sourceforge.net/docman/display_doc.php?docid=32071&group_id=22307
    especially threadsafety part why we create every time a new MySQL db connection object.
    """
    dbConn = MySQLdb.connect(host=self._db_server, \
                             user=self._db_user,\
                             passwd=self._db_passwd, \
                             db=self._db_name)
    return dbConn
    
  def get(self, cache_id, scope, default=None):
    sql_query = self.get_key_sql %(self._db_cache_table_name, cache_id, scope)
    cursor =  self.execSQLQuery(sql_query)
    if cursor:
      ## count return one row only
      result = cursor.fetchall()
      if 0 < len(result):
        ## we found results
        result = result[0]
        decoded_result = pickle.loads(base64.decodestring(result[0]))
        self.markCacheHit()
        cache_entry = CacheEntry(decoded_result, result[1], result[2])
        return cache_entry
      else:
        ## no such cache_id in DB
        return None
    else:
      ## DB not available
      return None
        
  def set(self, cache_id, scope, value, cache_duration=None, calculation_time=0):
    value = base64.encodestring(pickle.dumps(value,2))
    if not cache_duration:
      ## should live forever ==> setting cache_duration = 0 will make it live forever
      cache_duration = 0
    else:
      ## we have strict cache_duration defined. we calculate seconds since start of epoch
      cache_duration = int(cache_duration)
    ## Set key in DB
    stored_at = int(time.time())
    sql_query = self.insert_key_sql %(self._db_cache_table_name, cache_id, value, scope, stored_at, cache_duration, calculation_time)
    self.execSQLQuery(sql_query)
    self.markCacheMiss()
            
  def expireOldCacheEntries(self, forceCheck = False):
    now = time.time()
    if forceCheck or (now > (self._last_cache_expire_check_at + self.cache_expire_check_interval)):
      ## time to check for expired cache items
      #print "EXPIRE", self, self.cache_expire_check_interval
      self._last_cache_expire_check_at = now
      my_query = self.delete_expired_keys_sql %(self._db_cache_table_name, now)
      self.execSQLQuery(my_query)

  def delete(self, cache_id, scope):
    my_query = self.delete_key_sql %(self._db_cache_table_name, cache_id, scope)
    self.execSQLQuery(my_query)
    
  def has_key(self, cache_id, scope):
    my_query = self.has_key_sql %(self._db_cache_table_name, cache_id, scope)
    cursor =  self.execSQLQuery(my_query)
    if cursor:
      ## count() SQL function will return one row only
      result = cursor.fetchall()
      result = result[0][0] 
      if result == 0:
        ## no such key in DB
        return False
      elif result==1:
        ## we have this key in DB
        return True
      else:
        ## something wrong in DB model
        raise CachedMethodError, "Invalid cache table reltion format. cache_id MUST be unique!"
    else:
      ## DB not available
      return False

  def getScopeList(self):
    rl = []
    my_query = self.get_scope_list_sql %(self._db_cache_table_name)
    cursor =  self.execSQLQuery(my_query)
    results = cursor.fetchall() 
    for result in results:
        rl.append(result[0])
    return rl
    
  def getScopeKeyList(self, scope):
    rl = []
    my_query = self.get_scope_key_list_sql %(self._db_cache_table_name, scope)
    cursor =  self.execSQLQuery(my_query)
    results = cursor.fetchall() 
    for result in results:
        rl.append(result[0])
    return rl
    
  def clearCache(self):
    BaseCache.clearCache(self)
    ## SQL Cache is a persistent storage rather than delete all entries
    ## just expire them 
    ## self.expireOldCacheEntries(forceCheck = True):
    my_query = self.delete_all_keys_sql  %(self._db_cache_table_name)
    self.execSQLQuery(my_query)
    
  def clearCacheForScope(self, scope):
    my_query = self.delete_all_keys_for_scope_sql  %(self._db_cache_table_name, scope)
    self.execSQLQuery(my_query)

  def execSQLQuery(self, sql_query):
    """ 
    Try to execute sql query.
    Return cursor object because some queris can return result
    """
    dbConn = self.getCacheStorage()
    cursor = dbConn.cursor()
    cursor.execute(sql_query)
    return cursor