psycopgwrapper: Activate TCP keepalive on database connections

Turn on keepalive by default, to avoid hanged scripts in case of
network problems.

Also tune the keepalive timeouts smaller, on Linux at least,
so that the error happens after 5 min blackout.
(4 min idle + 4x15sec keepalive pings)

diff --git a/python/skytools/psycopgwrapper.py b/python/skytools/psycopgwrapper.py
index aeaa7a741ae946c7a347fe727fd634350f2b35ff..6aa5835b7162041838bca5e2e87b6f40cd72b3bf 100644 (file)
--- a/python/skytools/psycopgwrapper.py
+++ b/python/skytools/psycopgwrapper.py
@@ -62,6 +62,7 @@ __all__ = ['connect_database']
 # to the point of avoiding optimized access.
 # only backwards compat thing we need is dict* methods
 
+import socket
 import psycopg2.extensions, psycopg2.extras
 from skytools.sqltools import dbdict
 
@@ -102,10 +103,15 @@ class _CompatConnection(psycopg2.extensions.connection):
     def cursor(self):
         return psycopg2.extensions.connection.cursor(self, cursor_factory = _CompatCursor)
 
-def connect_database(connstr):
-    """Create a db connection with connect_timeout option.
+def connect_database(connstr, keepalive = True,
+                     tcp_keepidle = 4 * 60,     # 7200
+                     tcp_keepcnt = 4,           # 9
+                     tcp_keepintvl = 15):       # 75
+    """Create a db connection with connect_timeout and TCP keepalive.
     
     Default connect_timeout is 15, to change put it directly into dsn.
+
+    The extra tcp_* options are Linux-specific, see `man 7 tcp` for details.
     """
 
     # allow override
@@ -115,6 +121,16 @@ def connect_database(connstr):
     # create connection
     db = _CompatConnection(connstr)
 
+    # turn on keepalive on the connection
+    if keepalive and hasattr(socket, 'SO_KEEPALIVE'):
+        fd = db.cursor().fileno()
+        s = socket.fromfd(fd, socket.AF_INET, socket.SOCK_STREAM)
+        s.setsockopt(socket.SOL_SOCKET, socket.SO_KEEPALIVE, 1)
+        if hasattr(socket, 'TCP_KEEPCNT'):
+            s.setsockopt(socket.IPPROTO_TCP, socket.TCP_KEEPIDLE, tcp_keepidle)
+            s.setsockopt(socket.IPPROTO_TCP, socket.TCP_KEEPCNT, tcp_keepcnt)
+            s.setsockopt(socket.IPPROTO_TCP, socket.TCP_KEEPINTVL, tcp_keepintvl)
+
     # fill .server_version on older psycopg
     if not hasattr(db, 'server_version'):
         iso = db.isolation_level
@@ -123,5 +139,6 @@ def connect_database(connstr):
         curs.execute('show server_version_num')
         db.server_version = int(curs.fetchone()[0])
         db.set_isolation_level(iso)
+
     return db