indexer.py: Use psycopg2's execute_values to batch inserts

Batch inserts are much faster than a series of individual inserts
because they drastically reduce the overhead caused by round-trip
communication with the server. My tests in development confirm:

  - cursor.execute(): 19 seconds
  - execute_values(): 14 seconds

I'm currently only working with 4,500 rows, but I will experiment
with larger data sets, as well as larger batches. For example, on
the PostgreSQL mailing list a user reports doing 10,000 rows with
a page size of 100.

See: http://initd.org/psycopg/docs/extras.html#psycopg2.extras.execute_values
See: https://github.com/psycopg/psycopg2/issues/491#issuecomment-276551038

indexer.py

@@ -32,6 +32,7 @@
 
 from database import database_connection
 import json
+import psycopg2.extras
 from solr import solr_connection
 
 def index_views():
@@ -64,6 +65,9 @@ def index_views():
 
     cursor = db.cursor()
 
+    # create an empty list to store values for batch insertion
+    data = []
+
     while results_current_page <= results_num_pages:
         print('Indexing item views (page {} of {})'.format(results_current_page, results_num_pages))
 
@@ -84,12 +88,16 @@ def index_views():
         views = res.get_facets()
         # in this case iterate over the 'id' dict and get the item ids and views
         for item_id, item_views in views['id'].items():
-            cursor.execute('''INSERT INTO items(id, views) VALUES(%s, %s)
+            data.append((item_id, item_views))
-                           ON CONFLICT(id) DO UPDATE SET downloads=excluded.views''',
-                           (item_id, item_views))
 
+        # do a batch insert of values from the current "page" of results
+        sql = 'INSERT INTO items(id, views) VALUES %s ON CONFLICT(id) DO UPDATE SET downloads=excluded.views'
+        psycopg2.extras.execute_values(cursor, sql, data, template='(%s, %s)')
         db.commit()
 
+        # clear all items from the list so we can populate it with the next batch
+        data.clear()
+
         results_current_page += 1
 
     cursor.close()
@@ -119,6 +127,9 @@ def index_downloads():
 
     cursor = db.cursor()
 
+    # create an empty list to store values for batch insertion
+    data = []
+
     while results_current_page <= results_num_pages:
         print('Indexing item downloads (page {} of {})'.format(results_current_page, results_num_pages))
 
@@ -136,12 +147,16 @@ def index_downloads():
         downloads = res.get_facets()
         # in this case iterate over the 'owningItem' dict and get the item ids and downloads
         for item_id, item_downloads in downloads['owningItem'].items():
-            cursor.execute('''INSERT INTO items(id, downloads) VALUES(%s, %s)
+            data.append((item_id, item_downloads))
-                           ON CONFLICT(id) DO UPDATE SET downloads=excluded.downloads''',
-                           (item_id, item_downloads))
 
+        # do a batch insert of values from the current "page" of results
+        sql = 'INSERT INTO items(id, downloads) VALUES %s ON CONFLICT(id) DO UPDATE SET downloads=excluded.downloads'
+        psycopg2.extras.execute_values(cursor, sql, data, template='(%s, %s)')
         db.commit()
 
+        # clear all items from the list so we can populate it with the next batch
+        data.clear()
+
         results_current_page += 1
 
     cursor.close()