Faster asyncpg queries via a global connection pool

In my benchmarks I was able to obtain a 17% performance
improvement over the current asyncpg demo code with a shared
connection pool.

Resolves: #540
See also: #531

examples/sanic_asyncpg_example.py

@@ -1,11 +1,8 @@
-""" To run this example you need additional asyncpg package
-
-"""
 import os
 import asyncio
 
 import uvloop
-from asyncpg import connect
+from asyncpg import connect, create_pool
 
 from sanic import Sanic
 from sanic.response import json
@@ -18,39 +15,37 @@ DB_CONFIG = {
     'database': '<database>'
 }
 
+
 def jsonify(records):
     """
     Parse asyncpg record response into JSON format
     """
     return [dict(r.items()) for r in records]
 
+
 app = Sanic(__name__)
 
+
 @app.listener('before_server_start')
-async def create_db(app, loop):
-    """
-    Create some table and add some data
-    """
-    conn = await connect(**DB_CONFIG)
-    await conn.execute('DROP TABLE IF EXISTS sanic_post')
-    await conn.execute("""CREATE TABLE sanic_post (
-        id serial primary key,
-        content varchar(50),
-        post_date timestamp);"""
-                       )
-    for i in range(0, 100):
-        await conn.execute(f"""INSERT INTO sanic_post
-                           (id, content, post_date) VALUES ({i}, {i}, now())""")
-    await conn.close()
+async def register_db(app, loop):
+    app.pool = await create_pool(**DB_CONFIG, loop=loop, max_size=100)
+    async with app.pool.acquire() as connection:
+        await connection.execute('DROP TABLE IF EXISTS sanic_post')
+        await connection.execute("""CREATE TABLE sanic_post (
+                                id serial primary key,
+                                content varchar(50),
+                                post_date timestamp
+                            );""")
+        for i in range(0, 1000):
+            await connection.execute(f"""INSERT INTO sanic_post
+                (id, content, post_date) VALUES ({i}, {i}, now())""")
 
 
-@app.route("/")
-async def handler(request):
-    conn = await connect(**DB_CONFIG)
-    results = await conn.fetch('SELECT * FROM sanic_post')
-    await conn.close()
-    return json({'posts': jsonify(results)})
-
+@app.get('/')
+async def root_get(request):
+    async with app.pool.acquire() as connection:
+        results = await connection.fetch('SELECT * FROM sanic_post')
+        return json({'posts': jsonify(results)})
 
 if __name__ == '__main__':
-    app.run(host='0.0.0.0', port=8000)
+    app.run(host='127.0.0.1', port=8080)