From d5fb561709cf2181cd5b8fffd2cf70a3fb52e5ab Mon Sep 17 00:00:00 2001
From: Mark Haines <mark.haines@matrix.org>
Date: Mon, 20 Jun 2016 17:53:38 +0100
Subject: [PATCH] Optionally make committing to postgres asynchronous.

Useful when running tests when you don't care whether the server
will lose data that it claims that it has committed.
---
 synapse/storage/engines/__init__.py |  2 +-
 synapse/storage/engines/postgres.py | 13 ++++++++++++-
 synapse/storage/engines/sqlite3.py  |  2 +-
 3 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/synapse/storage/engines/__init__.py b/synapse/storage/engines/__init__.py
index 7bb5de1fe..338b49561 100644
--- a/synapse/storage/engines/__init__.py
+++ b/synapse/storage/engines/__init__.py
@@ -32,7 +32,7 @@ def create_engine(database_config):
 
     if engine_class:
         module = importlib.import_module(name)
-        return engine_class(module)
+        return engine_class(module, database_config)
 
     raise RuntimeError(
         "Unsupported database engine '%s'" % (name,)
diff --git a/synapse/storage/engines/postgres.py b/synapse/storage/engines/postgres.py
index c2290943b..a6ae79dfa 100644
--- a/synapse/storage/engines/postgres.py
+++ b/synapse/storage/engines/postgres.py
@@ -19,9 +19,10 @@ from ._base import IncorrectDatabaseSetup
 class PostgresEngine(object):
     single_threaded = False
 
-    def __init__(self, database_module):
+    def __init__(self, database_module, database_config):
         self.module = database_module
         self.module.extensions.register_type(self.module.extensions.UNICODE)
+        self.synchronous_commit = database_config.get("synchronous_commit", True)
 
     def check_database(self, txn):
         txn.execute("SHOW SERVER_ENCODING")
@@ -40,9 +41,19 @@ class PostgresEngine(object):
         db_conn.set_isolation_level(
             self.module.extensions.ISOLATION_LEVEL_REPEATABLE_READ
         )
+        # Asynchronous commit, don't wait for the server to call fsync before
+        # ending the transaction.
+        # https://www.postgresql.org/docs/current/static/wal-async-commit.html
+        if not self.synchronous_commit:
+            cursor = db_conn.cursor()
+            cursor.execute("SET synchronous_commit TO OFF")
+            cursor.close()
 
     def is_deadlock(self, error):
         if isinstance(error, self.module.DatabaseError):
+            # https://www.postgresql.org/docs/current/static/errcodes-appendix.html
+            # "40001" serialization_failure
+            # "40P01" deadlock_detected
             return error.pgcode in ["40001", "40P01"]
         return False
 
diff --git a/synapse/storage/engines/sqlite3.py b/synapse/storage/engines/sqlite3.py
index 14203aa50..755c9a1f0 100644
--- a/synapse/storage/engines/sqlite3.py
+++ b/synapse/storage/engines/sqlite3.py
@@ -21,7 +21,7 @@ import struct
 class Sqlite3Engine(object):
     single_threaded = True
 
-    def __init__(self, database_module):
+    def __init__(self, database_module, database_config):
         self.module = database_module
 
     def check_database(self, txn):