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# 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."""

import re
import time

from eventlet import greenthread
from sqlalchemy.exc import DisconnectionError, OperationalError
import sqlalchemy.interfaces
import sqlalchemy.orm
from sqlalchemy.pool import NullPool, StaticPool

import nova.exception
import nova.flags as flags
import nova.openstack.common.log as logging


FLAGS = flags.FLAGS
LOG = logging.getLogger(__name__)

_ENGINE = None
_MAKER = None


def get_session(autocommit=True, expire_on_commit=False):
    """Return a SQLAlchemy session."""
    global _MAKER

    if _MAKER is None:
        engine = get_engine()
        _MAKER = get_maker(engine, autocommit, expire_on_commit)

    session = _MAKER()
    session = wrap_session(session)
    return session


def wrap_session(session):
    """Return a session whose exceptions are wrapped."""
    session.query = nova.exception.wrap_db_error(session.query)
    session.flush = nova.exception.wrap_db_error(session.flush)
    return session


def get_engine():
    """Return a SQLAlchemy engine."""
    global _ENGINE
    if _ENGINE is None:
        _ENGINE = create_engine(FLAGS.sql_connection)
    return _ENGINE


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."""

    def regexp(expr, item):
        reg = re.compile(expr)
        return reg.search(unicode(item)) is not None
    dbapi_con.create_function('regexp', 2, regexp)


def greenthread_yield(dbapi_con, con_record):
    """
    Ensure other greenthreads get a chance to execute by forcing 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.
    """
    greenthread.sleep(0)


def ping_listener(dbapi_conn, connection_rec, connection_proxy):
    """
    Ensures that MySQL connections checked out of the
    pool are alive.

    Borrowed from:
    http://groups.google.com/group/sqlalchemy/msg/a4ce563d802c929f
    """
    try:
        dbapi_conn.cursor().execute('select 1')
    except dbapi_conn.OperationalError, ex:
        if ex.args[0] in (2006, 2013, 2014, 2045, 2055):
            LOG.warn('Got mysql server has gone away: %s', ex)
            raise DisconnectionError("Database server went away")
        else:
            raise


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.
    conn_err_codes = ('2002', '2003', '2006')
    for err_code in conn_err_codes:
        if args.find(err_code) != -1:
            return True
    return False


def create_engine(sql_connection):
    """Return a new SQLAlchemy engine."""
    connection_dict = sqlalchemy.engine.url.make_url(sql_connection)

    engine_args = {
        "pool_recycle": FLAGS.sql_idle_timeout,
        "echo": False,
        'convert_unicode': True,
    }

    # Map our SQL debug level to SQLAlchemy's options
    if FLAGS.sql_connection_debug >= 100:
        engine_args['echo'] = 'debug'
    elif FLAGS.sql_connection_debug >= 50:
        engine_args['echo'] = True

    if "sqlite" in connection_dict.drivername:
        engine_args["poolclass"] = NullPool

        if FLAGS.sql_connection == "sqlite://":
            engine_args["poolclass"] = StaticPool
            engine_args["connect_args"] = {'check_same_thread': False}

    engine = sqlalchemy.create_engine(sql_connection, **engine_args)

    sqlalchemy.event.listen(engine, 'checkin', greenthread_yield)

    if 'mysql' in connection_dict.drivername:
        sqlalchemy.event.listen(engine, 'checkout', ping_listener)
    elif 'sqlite' in connection_dict.drivername:
        if not FLAGS.sqlite_synchronous:
            sqlalchemy.event.listen(engine, 'connect',
                                    synchronous_switch_listener)
        sqlalchemy.event.listen(engine, 'connect', add_regexp_listener)

    if (FLAGS.sql_connection_trace and
            engine.dialect.dbapi.__name__ == 'MySQLdb'):
        import MySQLdb.cursors
        _do_query = debug_mysql_do_query()
        setattr(MySQLdb.cursors.BaseCursor, '_do_query', _do_query)

    try:
        engine.connect()
    except OperationalError, e:
        if not is_db_connection_error(e.args[0]):
            raise

        remaining = FLAGS.sql_max_retries
        if remaining == -1:
            remaining = 'infinite'
        while True:
            msg = _('SQL connection failed. %s attempts left.')
            LOG.warn(msg % remaining)
            if remaining != 'infinite':
                remaining -= 1
            time.sleep(FLAGS.sql_retry_interval)
            try:
                engine.connect()
                break
            except OperationalError, e:
                if (remaining != 'infinite' and remaining == 0) or \
                   not is_db_connection_error(e.args[0]):
                    raise
    return engine


def get_maker(engine, autocommit=True, expire_on_commit=False):
    """Return a SQLAlchemy sessionmaker using the given engine."""
    return sqlalchemy.orm.sessionmaker(bind=engine,
                                       autocommit=autocommit,
                                       expire_on_commit=expire_on_commit)


def debug_mysql_do_query():
    """Return a debug version of MySQLdb.cursors._do_query"""
    import MySQLdb.cursors
    import traceback

    old_mysql_do_query = MySQLdb.cursors.BaseCursor._do_query

    def _do_query(self, q):
        stack = ''
        for file, line, method, function in traceback.extract_stack():
            # exclude various common things from trace
            if file.endswith('session.py') and method == '_do_query':
                continue
            if file.endswith('api.py') and method == 'wrapper':
                continue
            if file.endswith('utils.py') and method == '_inner':
                continue
            if file.endswith('exception.py') and method == '_wrap':
                continue
            # nova/db/api is just a wrapper around nova/db/sqlalchemy/api
            if file.endswith('nova/db/api.py'):
                continue
            # only trace inside nova
            index = file.rfind('nova')
            if index == -1:
                continue
            stack += "File:%s:%s Method:%s() Line:%s | " \
                    % (file[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)

    # return the new _do_query method
    return _do_query
