Db txn set isolation level (#11799)

Co-authored-by: Brendan Abolivier <babolivier@matrix.org>
This commit is contained in:
Nick Barrett 2022-01-25 14:14:46 +00:00 committed by GitHub
parent fc8598bc87
commit b59d285f7c
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5 changed files with 61 additions and 5 deletions

1
changelog.d/11799.misc Normal file
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@ -0,0 +1 @@
Preparation for reducing Postgres serialization errors: allow setting transaction isolation level. Contributed by Nick @ Beeper.

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@ -702,6 +702,7 @@ class DatabasePool:
func: Callable[..., R],
*args: Any,
db_autocommit: bool = False,
isolation_level: Optional[int] = None,
**kwargs: Any,
) -> R:
"""Starts a transaction on the database and runs a given function
@ -724,6 +725,7 @@ class DatabasePool:
called multiple times if the transaction is retried, so must
correctly handle that case.
isolation_level: Set the server isolation level for this transaction.
args: positional args to pass to `func`
kwargs: named args to pass to `func`
@ -763,6 +765,7 @@ class DatabasePool:
func: Callable[..., R],
*args: Any,
db_autocommit: bool = False,
isolation_level: Optional[int] = None,
**kwargs: Any,
) -> R:
"""Wraps the .runWithConnection() method on the underlying db_pool.
@ -775,6 +778,7 @@ class DatabasePool:
db_autocommit: Whether to run the function in "autocommit" mode,
i.e. outside of a transaction. This is useful for transaction
that are only a single query. Currently only affects postgres.
isolation_level: Set the server isolation level for this transaction.
kwargs: named args to pass to `func`
Returns:
@ -834,6 +838,10 @@ class DatabasePool:
try:
if db_autocommit:
self.engine.attempt_to_set_autocommit(conn, True)
if isolation_level is not None:
self.engine.attempt_to_set_isolation_level(
conn, isolation_level
)
db_conn = LoggingDatabaseConnection(
conn, self.engine, "runWithConnection"
@ -842,6 +850,8 @@ class DatabasePool:
finally:
if db_autocommit:
self.engine.attempt_to_set_autocommit(conn, False)
if isolation_level:
self.engine.attempt_to_set_isolation_level(conn, None)
return await make_deferred_yieldable(
self._db_pool.runWithConnection(inner_func, *args, **kwargs)

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@ -12,11 +12,18 @@
# See the License for the specific language governing permissions and
# limitations under the License.
import abc
from typing import Generic, TypeVar
from enum import IntEnum
from typing import Generic, Optional, TypeVar
from synapse.storage.types import Connection
class IsolationLevel(IntEnum):
READ_COMMITTED: int = 1
REPEATABLE_READ: int = 2
SERIALIZABLE: int = 3
class IncorrectDatabaseSetup(RuntimeError):
pass
@ -109,3 +116,13 @@ class BaseDatabaseEngine(Generic[ConnectionType], metaclass=abc.ABCMeta):
commit/rollback the connections.
"""
...
@abc.abstractmethod
def attempt_to_set_isolation_level(
self, conn: Connection, isolation_level: Optional[int]
):
"""Attempt to set the connections isolation level.
Note: This has no effect on SQLite3, as transactions are SERIALIZABLE by default.
"""
...

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@ -13,8 +13,13 @@
# limitations under the License.
import logging
from typing import Mapping, Optional
from synapse.storage.engines._base import BaseDatabaseEngine, IncorrectDatabaseSetup
from synapse.storage.engines._base import (
BaseDatabaseEngine,
IncorrectDatabaseSetup,
IsolationLevel,
)
from synapse.storage.types import Connection
logger = logging.getLogger(__name__)
@ -34,6 +39,15 @@ class PostgresEngine(BaseDatabaseEngine):
self.synchronous_commit = database_config.get("synchronous_commit", True)
self._version = None # unknown as yet
self.isolation_level_map: Mapping[int, int] = {
IsolationLevel.READ_COMMITTED: self.module.extensions.ISOLATION_LEVEL_READ_COMMITTED,
IsolationLevel.REPEATABLE_READ: self.module.extensions.ISOLATION_LEVEL_REPEATABLE_READ,
IsolationLevel.SERIALIZABLE: self.module.extensions.ISOLATION_LEVEL_SERIALIZABLE,
}
self.default_isolation_level = (
self.module.extensions.ISOLATION_LEVEL_REPEATABLE_READ
)
@property
def single_threaded(self) -> bool:
return False
@ -104,9 +118,7 @@ class PostgresEngine(BaseDatabaseEngine):
return sql.replace("?", "%s")
def on_new_connection(self, db_conn):
db_conn.set_isolation_level(
self.module.extensions.ISOLATION_LEVEL_REPEATABLE_READ
)
db_conn.set_isolation_level(self.default_isolation_level)
# Set the bytea output to escape, vs the default of hex
cursor = db_conn.cursor()
@ -175,3 +187,12 @@ class PostgresEngine(BaseDatabaseEngine):
def attempt_to_set_autocommit(self, conn: Connection, autocommit: bool):
return conn.set_session(autocommit=autocommit) # type: ignore
def attempt_to_set_isolation_level(
self, conn: Connection, isolation_level: Optional[int]
):
if isolation_level is None:
isolation_level = self.default_isolation_level
else:
isolation_level = self.isolation_level_map[isolation_level]
return conn.set_isolation_level(isolation_level) # type: ignore

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@ -15,6 +15,7 @@ import platform
import struct
import threading
import typing
from typing import Optional
from synapse.storage.engines import BaseDatabaseEngine
from synapse.storage.types import Connection
@ -122,6 +123,12 @@ class Sqlite3Engine(BaseDatabaseEngine["sqlite3.Connection"]):
# set the connection to autocommit mode.
pass
def attempt_to_set_isolation_level(
self, conn: Connection, isolation_level: Optional[int]
):
# All transactions are SERIALIZABLE by default in sqllite
pass
# Following functions taken from: https://github.com/coleifer/peewee