From 0d75152d540a7d5dc9d1434e4d1a2941f5cf7355 Mon Sep 17 00:00:00 2001
From: Christopher Winslett <chris@compose.io>
Date: Mon, 16 Mar 2015 09:47:52 -0700
Subject: [PATCH] make healthiest node work

---
 helpers/etcd.py       | 20 ++++++++++++++------
 helpers/ha.py         |  2 +-
 helpers/postgresql.py | 21 ++++++++++++++++++++-
 3 files changed, 35 insertions(+), 8 deletions(-)

diff --git a/helpers/etcd.py b/helpers/etcd.py
index 909639ad..7abb12af 100644
--- a/helpers/etcd.py
+++ b/helpers/etcd.py
@@ -37,12 +37,6 @@ class Etcd:
     def client_url(self, path):
         return "http://%s/v2/keys/service/%s%s" % (self.host, self.scope, path)
 
-    def xlog_position(member):
-        try:
-            return self.get_client_path("/service/postgresql/xlog-position/%s" % member)["node"]["value"]
-        except urllib2.HTTPError:
-            return None
-
     def current_leader(self):
         try:
             hostname = self.get_client_path("/leader")["node"]["value"]
@@ -54,6 +48,20 @@ class Etcd:
                 return None
             raise helpers.errors.CurrentLeaderError("Etcd is not responding properly")
 
+    def members(self):
+        try:
+            members = []
+
+            r = self.get_client_path("/members?recursive=true")
+            for node in r["node"]["nodes"]:
+                members.append({"hostname": node["key"].split('/')[-1], "address": node["value"]})
+
+            return members
+        except urllib2.HTTPError as e:
+            if e.code == 404:
+                return None
+            raise helpers.errors.CurrentLeaderError("Etcd is not responding properly")
+
     def touch_member(self, member, connection_string):
         self.put_client_path("/members/%s" % member, {"value": connection_string})
 
diff --git a/helpers/ha.py b/helpers/ha.py
index f4d703ee..8ea95056 100644
--- a/helpers/ha.py
+++ b/helpers/ha.py
@@ -33,7 +33,7 @@ class Ha:
         try:
             if self.state_handler.is_healthy():
                 if self.is_unlocked():
-                    if self.state_handler.is_healthiest_node():
+                    if self.state_handler.is_healthiest_node(self.etcd.members()):
                         if self.acquire_lock():
                             if not self.state_handler.is_leader():
                                 self.state_handler.promote()
diff --git a/helpers/postgresql.py b/helpers/postgresql.py
index 01a0cc1f..85a301d5 100644
--- a/helpers/postgresql.py
+++ b/helpers/postgresql.py
@@ -104,7 +104,23 @@ class Postgresql:
 
         return True
 
-    def is_healthiest_node(self):
+    def is_healthiest_node(self, members):
+        for member in members:
+            if member["hostname"] == self.name:
+                continue
+            try:
+                member_conn = psycopg2.connect(member["address"])
+                member_conn.autocommit = True
+                member_cursor = member_conn.cursor()
+                member_cursor.execute("SELECT '%s'::pg_lsn - pg_last_xlog_replay_location() AS bytes;" % self.xlog_position())
+                xlog_diff = member_cursor.fetchone()[0]
+                print [self.name, member["hostname"], xlog_diff]
+                if xlog_diff  < 0:
+                    member_cursor.close()
+                    return False
+                member_cursor.close()
+            except psycopg2.OperationalError:
+                continue
         return True
 
     def replication_slot_name(self):
@@ -150,3 +166,6 @@ recovery_target_timeline = 'latest'
 
     def create_replication_user(self):
         self.query("CREATE USER \"%s\" WITH REPLICATION ENCRYPTED PASSWORD '%s';" % (self.replication["username"], self.replication["password"]))
+
+    def xlog_position(self):
+        return self.query("SELECT pg_last_xlog_replay_location();").fetchone()[0]