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OpenStack Study: session.py**** CubicPower OpenStack Study ****
# Copyright 2010 United States Government as represented by the # Administrator of the National Aeronautics and Space Administration. # All Rights Reserved. # # Licensed under the Apache License, Version 2.0 (the "License"); you may # not use this file except in compliance with the License. You may obtain # a copy of the License at # # http://www.apache.org/licenses/LICENSE-2.0 # # Unless required by applicable law or agreed to in writing, software # distributed under the License is distributed on an "AS IS" BASIS, WITHOUT # WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the # License for the specific language governing permissions and limitations # under the License. """Session Handling for SQLAlchemy backend. Recommended ways to use sessions within this framework: * Don't use them explicitly; this is like running with ``AUTOCOMMIT=1``. `model_query()` will implicitly use a session when called without one supplied. This is the ideal situation because it will allow queries to be automatically retried if the database connection is interrupted. .. note:: Automatic retry will be enabled in a future patch. It is generally fine to issue several queries in a row like this. Even though they may be run in separate transactions and/or separate sessions, each one will see the data from the prior calls. If needed, undo- or rollback-like functionality should be handled at a logical level. For an example, look at the code around quotas and `reservation_rollback()`. Examples: .. code:: python
**** CubicPower OpenStack Study **** class SqliteForeignKeysListener(PoolListener): """Ensures that the foreign key constraints are enforced in SQLite. The foreign key constraints are disabled by
**** CubicPower OpenStack Study **** def connect(self, dbapi_con, con_record): dbapi_con.execute('pragma foreign_keys=ON') # note(boris-42): In current versions of DB backends unique constraint # violation messages follow the structure: # # sqlite: # 1 column - (IntegrityError) column c1 is not unique # N columns - (IntegrityError) column c1, c2, ..., N are not unique # # sqlite since 3.7.16: # 1 column - (IntegrityError) UNIQUE constraint failed: tbl.k1 # # N columns - (IntegrityError) UNIQUE constraint failed: tbl.k1, tbl.k2 # # postgres: # 1 column - (IntegrityError) duplicate key value violates unique # constraint "users_c1_key" # N columns - (IntegrityError) duplicate key value violates unique # constraint "name_of_our_constraint" # # mysql: # 1 column - (IntegrityError) (1062, "Duplicate entry 'value_of_c1' for key # 'c1'") # N columns - (IntegrityError) (1062, "Duplicate entry 'values joined # with -' for key 'name_of_our_constraint'") # # ibm_db_sa: # N columns - (IntegrityError) SQL0803N One or more values in the INSERT # statement, UPDATE statement, or foreign key update caused by a # DELETE statement are not valid because the primary key, unique # constraint or unique index identified by "2" constrains table # "NOVA.KEY_PAIRS" from having duplicate values for the index # key. _DUP_KEY_RE_DB = { "sqlite": (re.compile(r"^.*columns?([^)]+)(is|are)\s+not\s+unique$"), re.compile(r"^.*UNIQUE\s+constraint\s+failed:\s+(.+)$")), "postgresql": (re.compile(r"^.*duplicate\s+key.*\"([^\"]+)\"\s*\n.*$"),), "mysql": (re.compile(r"^.*\(1062,.*'([^\']+)'\"\)$"),), "ibm_db_sa": (re.compile(r"^.*SQL0803N.*$"),), } def _raise_if_duplicate_entry_error(integrity_error, engine_name): """Raise exception if two entries are duplicated. In this function will be raised DBDuplicateEntry exception if integrity error wrap unique constraint violation. """
**** CubicPower OpenStack Study **** def _raise_if_duplicate_entry_error(integrity_error, engine_name): """Raise exception if two entries are duplicated. In this function will be raised DBDuplicateEntry exception if integrity error wrap unique constraint violation. """
**** CubicPower OpenStack Study **** def get_columns_from_uniq_cons_or_name(columns): # note(vsergeyev): UniqueConstraint name convention: "uniq_t0c10c2" # where `t` it is table name and columns `c1`, `c2` # are in UniqueConstraint. uniqbase = "uniq_" if not columns.startswith(uniqbase): if engine_name == "postgresql": return [columns[columns.index("_") + 1:columns.rindex("_")]] return [columns] return columns[len(uniqbase):].split("0")[1:] if engine_name not in ["ibm_db_sa", "mysql", "sqlite", "postgresql"]: return # FIXME(johannes): The usage of the .message attribute has been # deprecated since Python 2.6. However, the exceptions raised by # SQLAlchemy can differ when using unicode() and accessing .message. # An audit across all three supported engines will be necessary to # ensure there are no regressions. for pattern in _DUP_KEY_RE_DB[engine_name]: match = pattern.match(integrity_error.message) if match: break else: return # NOTE(mriedem): The ibm_db_sa integrity error message doesn't provide the # columns so we have to omit that from the DBDuplicateEntry error. columns = '' if engine_name != 'ibm_db_sa': columns = match.group(1) if engine_name == "sqlite": columns = [c.split('.')[-1] for c in columns.strip().split(", ")] else: columns = get_columns_from_uniq_cons_or_name(columns) raise exception.DBDuplicateEntry(columns, integrity_error) # NOTE(comstud): In current versions of DB backends, Deadlock violation # messages follow the structure: # # mysql: # (OperationalError) (1213, 'Deadlock found when trying to get lock; try ' # 'restarting transaction') _DEADLOCK_RE_DB = { "mysql": re.compile(r"^.*\(1213, 'Deadlock.*") } def _raise_if_deadlock_error(operational_error, engine_name): """Raise exception on deadlock condition. Raise DBDeadlock exception if OperationalError contains a Deadlock condition. """ re = _DEADLOCK_RE_DB.get(engine_name) if re is None: return # FIXME(johannes): The usage of the .message attribute has been # deprecated since Python 2.6. However, the exceptions raised by # SQLAlchemy can differ when using unicode() and accessing .message. # An audit across all three supported engines will be necessary to # ensure there are no regressions. m = re.match(operational_error.message) if not m: return raise exception.DBDeadlock(operational_error) def _wrap_db_error(f): #TODO(rpodolyaka): in a subsequent commit make this a class decorator to # ensure it can only applied to Session subclasses instances (as we use # Session instance bind attribute below) @functools.wraps(f)
**** CubicPower OpenStack Study **** def _raise_if_deadlock_error(operational_error, engine_name): """Raise exception on deadlock condition. Raise DBDeadlock exception if OperationalError contains a Deadlock condition. """ re = _DEADLOCK_RE_DB.get(engine_name) if re is None: return # FIXME(johannes): The usage of the .message attribute has been # deprecated since Python 2.6. However, the exceptions raised by # SQLAlchemy can differ when using unicode() and accessing .message. # An audit across all three supported engines will be necessary to # ensure there are no regressions. m = re.match(operational_error.message) if not m: return raise exception.DBDeadlock(operational_error)
**** CubicPower OpenStack Study **** def _wrap_db_error(f): #TODO(rpodolyaka): in a subsequent commit make this a class decorator to # ensure it can only applied to Session subclasses instances (as we use # Session instance bind attribute below) @functools.wraps(f)
**** CubicPower OpenStack Study **** def _wrap(self, *args, **kwargs): try: return f(self, *args, **kwargs) except UnicodeEncodeError: raise exception.DBInvalidUnicodeParameter() except sqla_exc.OperationalError as e: _raise_if_db_connection_lost(e, self.bind) _raise_if_deadlock_error(e, self.bind.dialect.name) # NOTE(comstud): A lot of code is checking for OperationalError # so let's not wrap it for now. raise # note(boris-42): We should catch unique constraint violation and # wrap it by our own DBDuplicateEntry exception. Unique constraint # violation is wrapped by IntegrityError. except sqla_exc.IntegrityError as e: # note(boris-42): SqlAlchemy doesn't unify errors from different # DBs so we must do this. Also in some tables (for example # instance_types) there are more than one unique constraint. This # means we should get names of columns, which values violate # unique constraint, from error message. _raise_if_duplicate_entry_error(e, self.bind.dialect.name) raise exception.DBError(e) except Exception as e: LOG.exception(_LE('DB exception wrapped.')) raise exception.DBError(e) return _wrap def _synchronous_switch_listener(dbapi_conn, connection_rec): """Switch sqlite connections to non-synchronous mode.""" dbapi_conn.execute("PRAGMA synchronous = OFF") def _add_regexp_listener(dbapi_con, con_record): """Add REGEXP function to sqlite connections."""
**** CubicPower OpenStack Study **** def _synchronous_switch_listener(dbapi_conn, connection_rec): """Switch sqlite connections to non-synchronous mode.""" dbapi_conn.execute("PRAGMA synchronous = OFF")
**** CubicPower OpenStack Study **** def _add_regexp_listener(dbapi_con, con_record): """Add REGEXP function to sqlite connections."""
**** CubicPower OpenStack Study **** def regexp(expr, item): reg = re.compile(expr) return reg.search(six.text_type(item)) is not None dbapi_con.create_function('regexp', 2, regexp) def _thread_yield(dbapi_con, con_record): """Ensure other greenthreads get a chance to be executed. If we use eventlet.monkey_patch(), eventlet.greenthread.sleep(0) will execute instead of time.sleep(0). Force a context switch. With common database backends (eg MySQLdb and sqlite), there is no implicit yield caused by network I/O since they are implemented by C libraries that eventlet cannot monkey patch. """ time.sleep(0) def _ping_listener(engine, dbapi_conn, connection_rec, connection_proxy): """Ensures that MySQL and DB2 connections are alive. Borrowed from: http://groups.google.com/group/sqlalchemy/msg/a4ce563d802c929f """ cursor = dbapi_conn.cursor() try: ping_sql = 'select 1' if engine.name == 'ibm_db_sa': # DB2 requires a table expression ping_sql = 'select 1 from (values (1)) AS t1' cursor.execute(ping_sql) except Exception as ex: if engine.dialect.is_disconnect(ex, dbapi_conn, cursor): msg = _LW('Database server has gone away: %s') % ex LOG.warning(msg) raise sqla_exc.DisconnectionError(msg) else: raise def _set_mode_traditional(dbapi_con, connection_rec, connection_proxy): """Set engine mode to 'traditional'. Required to prevent silent truncates at insert or update operations under MySQL. By default MySQL truncates inserted string if it longer than a declared field just with warning. That is fraught with data corruption. """ _set_session_sql_mode(dbapi_con, connection_rec, connection_proxy, 'TRADITIONAL') def _set_session_sql_mode(dbapi_con, connection_rec, connection_proxy, sql_mode=None): """Set the sql_mode session variable. MySQL supports several server modes. The default is None, but sessions may choose to enable server modes like TRADITIONAL, ANSI, several STRICT_* modes and others. Note: passing in '' (empty string) for sql_mode clears the SQL mode for the session, overriding a potentially set server default. Passing in None (the default) makes this a no-op, meaning if a server-side SQL mode is set, it still applies. """ cursor = dbapi_con.cursor() if sql_mode is not None: cursor.execute("SET SESSION sql_mode = %s", [sql_mode]) # Check against the real effective SQL mode. Even when unset by # our own config, the server may still be operating in a specific # SQL mode as set by the server configuration cursor.execute("SHOW VARIABLES LIKE 'sql_mode'") row = cursor.fetchone() if row is None: LOG.warning(_LW('Unable to detect effective SQL mode')) return realmode = row[1] LOG.info(_LI('MySQL server mode set to %s') % realmode) # 'TRADITIONAL' mode enables several other modes, so # we need a substring match here if not ('TRADITIONAL' in realmode.upper() or 'STRICT_ALL_TABLES' in realmode.upper()): LOG.warning(_LW("MySQL SQL mode is '%s', " "consider enabling TRADITIONAL or STRICT_ALL_TABLES") % realmode) def _is_db_connection_error(args): """Return True if error in connecting to db.""" # NOTE(adam_g): This is currently MySQL specific and needs to be extended # to support Postgres and others. # For the db2, the error code is -30081 since the db2 is still not ready conn_err_codes = ('2002', '2003', '2006', '2013', '-30081') for err_code in conn_err_codes: if args.find(err_code) != -1: return True return False def _raise_if_db_connection_lost(error, engine): # NOTE(vsergeyev): Function is_disconnect(e, connection, cursor) # requires connection and cursor in incoming parameters, # but we have no possibility to create connection if DB # is not available, so in such case reconnect fails. # But is_disconnect() ignores these parameters, so it # makes sense to pass to function None as placeholder # instead of connection and cursor. if engine.dialect.is_disconnect(error, None, None): raise exception.DBConnectionError(error) def create_engine(sql_connection, sqlite_fk=False, mysql_sql_mode=None, mysql_traditional_mode=False, idle_timeout=3600, connection_debug=0, max_pool_size=None, max_overflow=None, pool_timeout=None, sqlite_synchronous=True, connection_trace=False, max_retries=10, retry_interval=10): """Return a new SQLAlchemy engine.""" connection_dict = sqlalchemy.engine.url.make_url(sql_connection) engine_args = { "pool_recycle": idle_timeout, 'convert_unicode': True, } logger = logging.getLogger('sqlalchemy.engine') # Map SQL debug level to Python log level if connection_debug >= 100: logger.setLevel(logging.DEBUG) elif connection_debug >= 50: logger.setLevel(logging.INFO) else: logger.setLevel(logging.WARNING) if "sqlite" in connection_dict.drivername: if sqlite_fk: engine_args["listeners"] = [SqliteForeignKeysListener()] engine_args["poolclass"] = NullPool if sql_connection == "sqlite://": engine_args["poolclass"] = StaticPool engine_args["connect_args"] = {'check_same_thread': False} else: if max_pool_size is not None: engine_args['pool_size'] = max_pool_size if max_overflow is not None: engine_args['max_overflow'] = max_overflow if pool_timeout is not None: engine_args['pool_timeout'] = pool_timeout engine = sqlalchemy.create_engine(sql_connection, **engine_args) sqlalchemy.event.listen(engine, 'checkin', _thread_yield) if engine.name in ['mysql', 'ibm_db_sa']: ping_callback = functools.partial(_ping_listener, engine) sqlalchemy.event.listen(engine, 'checkout', ping_callback) if engine.name == 'mysql': if mysql_traditional_mode: mysql_sql_mode = 'TRADITIONAL' if mysql_sql_mode: mode_callback = functools.partial(_set_session_sql_mode, sql_mode=mysql_sql_mode) sqlalchemy.event.listen(engine, 'checkout', mode_callback) elif 'sqlite' in connection_dict.drivername: if not sqlite_synchronous: sqlalchemy.event.listen(engine, 'connect', _synchronous_switch_listener) sqlalchemy.event.listen(engine, 'connect', _add_regexp_listener) if connection_trace and engine.dialect.dbapi.__name__ == 'MySQLdb': _patch_mysqldb_with_stacktrace_comments() try: engine.connect() except sqla_exc.OperationalError as e: if not _is_db_connection_error(e.args[0]): raise remaining = max_retries if remaining == -1: remaining = 'infinite' while True: msg = _LW('SQL connection failed. %s attempts left.') LOG.warning(msg % remaining) if remaining != 'infinite': remaining -= 1 time.sleep(retry_interval) try: engine.connect() break except sqla_exc.OperationalError as e: if (remaining != 'infinite' and remaining == 0) or \ not _is_db_connection_error(e.args[0]): raise return engine
**** CubicPower OpenStack Study **** def _thread_yield(dbapi_con, con_record): """Ensure other greenthreads get a chance to be executed. If we use eventlet.monkey_patch(), eventlet.greenthread.sleep(0) will execute instead of time.sleep(0). Force a context switch. With common database backends (eg MySQLdb and sqlite), there is no implicit yield caused by network I/O since they are implemented by C libraries that eventlet cannot monkey patch. """ time.sleep(0)
**** CubicPower OpenStack Study **** def _ping_listener(engine, dbapi_conn, connection_rec, connection_proxy): """Ensures that MySQL and DB2 connections are alive. Borrowed from: http://groups.google.com/group/sqlalchemy/msg/a4ce563d802c929f """ cursor = dbapi_conn.cursor() try: ping_sql = 'select 1' if engine.name == 'ibm_db_sa': # DB2 requires a table expression ping_sql = 'select 1 from (values (1)) AS t1' cursor.execute(ping_sql) except Exception as ex: if engine.dialect.is_disconnect(ex, dbapi_conn, cursor): msg = _LW('Database server has gone away: %s') % ex LOG.warning(msg) raise sqla_exc.DisconnectionError(msg) else: raise
**** CubicPower OpenStack Study **** def _set_mode_traditional(dbapi_con, connection_rec, connection_proxy): """Set engine mode to 'traditional'. Required to prevent silent truncates at insert or update operations under MySQL. By default MySQL truncates inserted string if it longer than a declared field just with warning. That is fraught with data corruption. """ _set_session_sql_mode(dbapi_con, connection_rec, connection_proxy, 'TRADITIONAL')
**** CubicPower OpenStack Study **** def _set_session_sql_mode(dbapi_con, connection_rec, connection_proxy, sql_mode=None): """Set the sql_mode session variable. MySQL supports several server modes. The default is None, but sessions may choose to enable server modes like TRADITIONAL, ANSI, several STRICT_* modes and others. Note: passing in '' (empty string) for sql_mode clears the SQL mode for the session, overriding a potentially set server default. Passing in None (the default) makes this a no-op, meaning if a server-side SQL mode is set, it still applies. """ cursor = dbapi_con.cursor() if sql_mode is not None: cursor.execute("SET SESSION sql_mode = %s", [sql_mode]) # Check against the real effective SQL mode. Even when unset by # our own config, the server may still be operating in a specific # SQL mode as set by the server configuration cursor.execute("SHOW VARIABLES LIKE 'sql_mode'") row = cursor.fetchone() if row is None: LOG.warning(_LW('Unable to detect effective SQL mode')) return realmode = row[1] LOG.info(_LI('MySQL server mode set to %s') % realmode) # 'TRADITIONAL' mode enables several other modes, so # we need a substring match here if not ('TRADITIONAL' in realmode.upper() or 'STRICT_ALL_TABLES' in realmode.upper()): LOG.warning(_LW("MySQL SQL mode is '%s', " "consider enabling TRADITIONAL or STRICT_ALL_TABLES") % realmode)
**** CubicPower OpenStack Study **** def _is_db_connection_error(args): """Return True if error in connecting to db.""" # NOTE(adam_g): This is currently MySQL specific and needs to be extended # to support Postgres and others. # For the db2, the error code is -30081 since the db2 is still not ready conn_err_codes = ('2002', '2003', '2006', '2013', '-30081') for err_code in conn_err_codes: if args.find(err_code) != -1: return True return False
**** CubicPower OpenStack Study **** def _raise_if_db_connection_lost(error, engine): # NOTE(vsergeyev): Function is_disconnect(e, connection, cursor) # requires connection and cursor in incoming parameters, # but we have no possibility to create connection if DB # is not available, so in such case reconnect fails. # But is_disconnect() ignores these parameters, so it # makes sense to pass to function None as placeholder # instead of connection and cursor. if engine.dialect.is_disconnect(error, None, None): raise exception.DBConnectionError(error)
**** CubicPower OpenStack Study **** def create_engine(sql_connection, sqlite_fk=False, mysql_sql_mode=None, mysql_traditional_mode=False, idle_timeout=3600, connection_debug=0, max_pool_size=None, max_overflow=None, pool_timeout=None, sqlite_synchronous=True, connection_trace=False, max_retries=10, retry_interval=10): """Return a new SQLAlchemy engine.""" connection_dict = sqlalchemy.engine.url.make_url(sql_connection) engine_args = { "pool_recycle": idle_timeout, 'convert_unicode': True, } logger = logging.getLogger('sqlalchemy.engine') # Map SQL debug level to Python log level if connection_debug >= 100: logger.setLevel(logging.DEBUG) elif connection_debug >= 50: logger.setLevel(logging.INFO) else: logger.setLevel(logging.WARNING) if "sqlite" in connection_dict.drivername: if sqlite_fk: engine_args["listeners"] = [SqliteForeignKeysListener()] engine_args["poolclass"] = NullPool if sql_connection == "sqlite://": engine_args["poolclass"] = StaticPool engine_args["connect_args"] = {'check_same_thread': False} else: if max_pool_size is not None: engine_args['pool_size'] = max_pool_size if max_overflow is not None: engine_args['max_overflow'] = max_overflow if pool_timeout is not None: engine_args['pool_timeout'] = pool_timeout engine = sqlalchemy.create_engine(sql_connection, **engine_args) sqlalchemy.event.listen(engine, 'checkin', _thread_yield) if engine.name in ['mysql', 'ibm_db_sa']: ping_callback = functools.partial(_ping_listener, engine) sqlalchemy.event.listen(engine, 'checkout', ping_callback) if engine.name == 'mysql': if mysql_traditional_mode: mysql_sql_mode = 'TRADITIONAL' if mysql_sql_mode: mode_callback = functools.partial(_set_session_sql_mode, sql_mode=mysql_sql_mode) sqlalchemy.event.listen(engine, 'checkout', mode_callback) elif 'sqlite' in connection_dict.drivername: if not sqlite_synchronous: sqlalchemy.event.listen(engine, 'connect', _synchronous_switch_listener) sqlalchemy.event.listen(engine, 'connect', _add_regexp_listener) if connection_trace and engine.dialect.dbapi.__name__ == 'MySQLdb': _patch_mysqldb_with_stacktrace_comments() try: engine.connect() except sqla_exc.OperationalError as e: if not _is_db_connection_error(e.args[0]): raise remaining = max_retries if remaining == -1: remaining = 'infinite' while True: msg = _LW('SQL connection failed. %s attempts left.') LOG.warning(msg % remaining) if remaining != 'infinite': remaining -= 1 time.sleep(retry_interval) try: engine.connect() break except sqla_exc.OperationalError as e: if (remaining != 'infinite' and remaining == 0) or \ not _is_db_connection_error(e.args[0]): raise return engine
**** CubicPower OpenStack Study **** class Query(sqlalchemy.orm.query.Query): """Subclass of sqlalchemy.query with soft_delete() method."""
**** CubicPower OpenStack Study **** def soft_delete(self, synchronize_session='evaluate'): return self.update({'deleted': literal_column('id'), 'updated_at': literal_column('updated_at'), 'deleted_at': timeutils.utcnow()}, synchronize_session=synchronize_session)
**** CubicPower OpenStack Study **** class Session(sqlalchemy.orm.session.Session): """Custom Session class to avoid SqlAlchemy Session monkey patching.""" @_wrap_db_error
**** CubicPower OpenStack Study **** def query(self, *args, **kwargs): return super(Session, self).query(*args, **kwargs) @_wrap_db_error
**** CubicPower OpenStack Study **** def flush(self, *args, **kwargs): return super(Session, self).flush(*args, **kwargs) @_wrap_db_error
**** CubicPower OpenStack Study **** def execute(self, *args, **kwargs): return super(Session, self).execute(*args, **kwargs) def get_maker(engine, autocommit=True, expire_on_commit=False): """Return a SQLAlchemy sessionmaker using the given engine.""" return sqlalchemy.orm.sessionmaker(bind=engine, class_=Session, autocommit=autocommit, expire_on_commit=expire_on_commit, query_cls=Query) def _patch_mysqldb_with_stacktrace_comments(): """Adds current stack trace as a comment in queries. Patches MySQLdb.cursors.BaseCursor._do_query. """ import MySQLdb.cursors import traceback old_mysql_do_query = MySQLdb.cursors.BaseCursor._do_query
**** CubicPower OpenStack Study **** def get_maker(engine, autocommit=True, expire_on_commit=False): """Return a SQLAlchemy sessionmaker using the given engine.""" return sqlalchemy.orm.sessionmaker(bind=engine, class_=Session, autocommit=autocommit, expire_on_commit=expire_on_commit, query_cls=Query)
**** CubicPower OpenStack Study **** def _patch_mysqldb_with_stacktrace_comments(): """Adds current stack trace as a comment in queries. Patches MySQLdb.cursors.BaseCursor._do_query. """ import MySQLdb.cursors import traceback old_mysql_do_query = MySQLdb.cursors.BaseCursor._do_query
**** CubicPower OpenStack Study **** def _do_query(self, q): stack = '' for filename, line, method, function in traceback.extract_stack(): # exclude various common things from trace if filename.endswith('session.py') and method == '_do_query': continue if filename.endswith('api.py') and method == 'wrapper': continue if filename.endswith('utils.py') and method == '_inner': continue if filename.endswith('exception.py') and method == '_wrap': continue # db/api is just a wrapper around db/sqlalchemy/api if filename.endswith('db/api.py'): continue # only trace inside nova index = filename.rfind('nova') if index == -1: continue stack += "File:%s:%s Method:%s() Line:%s | " \ % (filename[index:], line, method, function) # strip trailing " | " from stack if stack: stack = stack[:-3] qq = "%s /* %s */" % (q, stack) else: qq = q old_mysql_do_query(self, qq) setattr(MySQLdb.cursors.BaseCursor, '_do_query', _do_query)
**** CubicPower OpenStack Study **** class EngineFacade(object): """A helper class for removing of global engine instances from nova.db. As a library, nova.db can't decide where to store/when to create engine and sessionmaker instances, so this must be left for a target application. On the other hand, in order to simplify the adoption of nova.db changes, we'll provide a helper class, which creates engine and sessionmaker on its instantiation and provides get_engine()/get_session() methods that are compatible with corresponding utility functions that currently exist in target projects, e.g. in Nova. engine/sessionmaker instances will still be global (and they are meant to be global), but they will be stored in the app context, rather that in the nova.db context. Note: using of this helper is completely optional and you are encouraged to integrate engine/sessionmaker instances into your apps any way you like (e.g. one might want to bind a session to a request context). Two important things to remember: 1. An Engine instance is effectively a pool of DB connections, so it's meant to be shared (and it's thread-safe). 2. A Session instance is not meant to be shared and represents a DB transactional context (i.e. it's not thread-safe). sessionmaker is a factory of sessions. """
**** CubicPower OpenStack Study **** def __init__(self, sql_connection, sqlite_fk=False, mysql_sql_mode=None, autocommit=True, expire_on_commit=False, **kwargs): """Initialize engine and sessionmaker instances. :param sqlite_fk: enable foreign keys in SQLite :type sqlite_fk: bool :param mysql_sql_mode: set SQL mode in MySQL :type mysql_sql_mode: string :param autocommit: use autocommit mode for created Session instances :type autocommit: bool :param expire_on_commit: expire session objects on commit :type expire_on_commit: bool Keyword arguments: :keyword idle_timeout: timeout before idle sql connections are reaped (defaults to 3600) :keyword connection_debug: verbosity of SQL debugging information. 0=None, 100=Everything (defaults to 0) :keyword max_pool_size: maximum number of SQL connections to keep open in a pool (defaults to SQLAlchemy settings) :keyword max_overflow: if set, use this value for max_overflow with sqlalchemy (defaults to SQLAlchemy settings) :keyword pool_timeout: if set, use this value for pool_timeout with sqlalchemy (defaults to SQLAlchemy settings) :keyword sqlite_synchronous: if True, SQLite uses synchronous mode (defaults to True) :keyword connection_trace: add python stack traces to SQL as comment strings (defaults to False) :keyword max_retries: maximum db connection retries during startup. (setting -1 implies an infinite retry count) (defaults to 10) :keyword retry_interval: interval between retries of opening a sql connection (defaults to 10) """ super(EngineFacade, self).__init__() self._engine = create_engine( sql_connection=sql_connection, sqlite_fk=sqlite_fk, mysql_sql_mode=mysql_sql_mode, idle_timeout=kwargs.get('idle_timeout', 3600), connection_debug=kwargs.get('connection_debug', 0), max_pool_size=kwargs.get('max_pool_size'), max_overflow=kwargs.get('max_overflow'), pool_timeout=kwargs.get('pool_timeout'), sqlite_synchronous=kwargs.get('sqlite_synchronous', True), connection_trace=kwargs.get('connection_trace', False), max_retries=kwargs.get('max_retries', 10), retry_interval=kwargs.get('retry_interval', 10)) self._session_maker = get_maker( engine=self._engine, autocommit=autocommit, expire_on_commit=expire_on_commit)
**** CubicPower OpenStack Study **** def get_engine(self): """Get the engine instance (note, that it's shared).""" return self._engine
**** CubicPower OpenStack Study **** def get_session(self, **kwargs): """Get a Session instance. If passed, keyword arguments values override the ones used when the sessionmaker instance was created. :keyword autocommit: use autocommit mode for created Session instances :type autocommit: bool :keyword expire_on_commit: expire session objects on commit :type expire_on_commit: bool """ for arg in kwargs: if arg not in ('autocommit', 'expire_on_commit'): del kwargs[arg] return self._session_maker(**kwargs)
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