Add retry to migrate_word_counts

db/migrate/20131210181901_migrate_word_counts.rb

@@ -5,13 +5,27 @@ class MigrateWordCounts < ActiveRecord::Migration
 
     post_ids = execute("SELECT id FROM posts WHERE word_count IS NULL LIMIT 500").map {|r| r['id'].to_i }
     while post_ids.length > 0
+      3.times do
+        begin
           execute "UPDATE posts SET word_count = COALESCE(array_length(regexp_split_to_array(raw, ' '),1), 0) WHERE id IN (#{post_ids.join(',')})"
+          break
+        rescue PG::Error
+          # Deadlock. Try again, up to 3 times.
+        end
+      end
       post_ids = execute("SELECT id FROM posts WHERE word_count IS NULL LIMIT 500").map {|r| r['id'].to_i }
     end
 
     topic_ids = execute("SELECT id FROM topics WHERE word_count IS NULL LIMIT 500").map {|r| r['id'].to_i }
     while topic_ids.length > 0
+      3.times do
+        begin
           execute "UPDATE topics SET word_count = COALESCE((SELECT SUM(COALESCE(posts.word_count, 0)) FROM posts WHERE posts.topic_id = topics.id), 0) WHERE topics.id IN (#{topic_ids.join(',')})"
+          break
+        rescue PG::Error
+          # Deadlock. Try again, up to 3 times.
+        end
+      end
       topic_ids = execute("SELECT id FROM topics WHERE word_count IS NULL LIMIT 500").map {|r| r['id'].to_i }
     end