diff --git a/changelog.d/11799.misc b/changelog.d/11799.misc
new file mode 100644
index 0000000000..5c3b2bcaf4
--- /dev/null
+++ b/changelog.d/11799.misc
@@ -0,0 +1 @@
+Preparation for reducing Postgres serialization errors: allow setting transaction isolation level. Contributed by Nick @ Beeper.
diff --git a/synapse/storage/database.py b/synapse/storage/database.py
index 57cc1d76e0..7455326ed3 100644
--- a/synapse/storage/database.py
+++ b/synapse/storage/database.py
@@ -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)
diff --git a/synapse/storage/engines/_base.py b/synapse/storage/engines/_base.py
index 20cd63c330..143cd98ca2 100644
--- a/synapse/storage/engines/_base.py
+++ b/synapse/storage/engines/_base.py
@@ -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.
+ """
+ ...
diff --git a/synapse/storage/engines/postgres.py b/synapse/storage/engines/postgres.py
index b3d71f661c..808342fafb 100644
--- a/synapse/storage/engines/postgres.py
+++ b/synapse/storage/engines/postgres.py
@@ -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
diff --git a/synapse/storage/engines/sqlite.py b/synapse/storage/engines/sqlite.py
index 70d17d4f2c..6c19e55999 100644
--- a/synapse/storage/engines/sqlite.py
+++ b/synapse/storage/engines/sqlite.py
@@ -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
|
