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# Copyright 2015 Oliver Cope
#
# 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.
import time
from datetime import datetime
from yoyo import exceptions
from yoyo.backends.core.postgresql import PostgresqlBackend
class RedshiftBackend(PostgresqlBackend):
def list_tables(self):
current_schema = self.execute("SELECT current_schema()").fetchone()[0]
return super(PostgresqlBackend, self).list_tables(schema=current_schema)
# Redshift does not support ROLLBACK TO SAVEPOINT
def savepoint(self, id):
pass
def savepoint_release(self, id):
pass
def savepoint_rollback(self, id):
self.rollback()
# Redshift does not enforce primary and unique keys
def _insert_lock_row(self, pid, timeout, poll_interval=0.5):
poll_interval = min(poll_interval, timeout)
started = time.time()
while True:
with self.transaction():
# prevents isolation violation errors
self.execute("LOCK {}".format(self.lock_table_quoted))
cursor = self.execute(
"SELECT pid FROM {}".format(self.lock_table_quoted)
)
row = cursor.fetchone()
if not row:
self.execute(
"INSERT INTO {} (locked, ctime, pid) "
"VALUES (1, :when, :pid)".format(self.lock_table_quoted),
{"when": datetime.utcnow(), "pid": pid},
)
return
elif timeout and time.time() > started + timeout:
raise exceptions.LockTimeout(
"Process {} has locked this database "
"(run yoyo break-lock to remove this lock)".format(row[0])
)
else:
time.sleep(poll_interval)
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