From 49d6aa1394bba42d52cae4013f7103d682756b28 Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Tue, 7 Apr 2015 15:28:37 +0100
Subject: [PATCH] Retry on deadlock

---
 synapse/storage/_base.py           | 16 +++++++++++++---
 synapse/storage/engines/maria.py   |  5 +++++
 synapse/storage/engines/sqlite3.py |  3 +++
 3 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/synapse/storage/_base.py b/synapse/storage/_base.py
index 4ac61be89..c15cec0c7 100644
--- a/synapse/storage/_base.py
+++ b/synapse/storage/_base.py
@@ -160,9 +160,19 @@ class LoggingTransaction(object):
         start = time.time() * 1000
 
         try:
-            return self.txn.execute(
-                sql, *args, **kwargs
-            )
+            i = 0
+            N = 5
+            while True:
+                try:
+                    return self.txn.execute(
+                        sql, *args, **kwargs
+                    )
+                except self.database_engine.module.DatabaseError as e:
+                    if self.database_engine.is_deadlock(e) and i < N:
+                        i += 1
+                        logger.warn("[SQL DEADLOCK] {%s}", self.name)
+                        continue
+                    raise
         except Exception as e:
                 logger.debug("[SQL FAIL] {%s} %s", self.name, e)
                 raise
diff --git a/synapse/storage/engines/maria.py b/synapse/storage/engines/maria.py
index 7fcb706a6..a279bfaf4 100644
--- a/synapse/storage/engines/maria.py
+++ b/synapse/storage/engines/maria.py
@@ -40,3 +40,8 @@ class MariaEngine(object):
         )
         db_conn.commit()
         prepare_database(db_conn, self)
+
+    def is_deadlock(self, error):
+        if isinstance(error, self.module.InternalError):
+            return error.sqlstate == 40001 and error.errno == 1213
+        return False
diff --git a/synapse/storage/engines/sqlite3.py b/synapse/storage/engines/sqlite3.py
index e802b5d5f..72c11df46 100644
--- a/synapse/storage/engines/sqlite3.py
+++ b/synapse/storage/engines/sqlite3.py
@@ -32,3 +32,6 @@ class Sqlite3Engine(object):
     def prepare_database(self, db_conn):
         prepare_sqlite3_database(db_conn)
         prepare_database(db_conn, self)
+
+    def is_deadlock(self, error):
+        return False