Add script to migrate nonce to addresses

This script copy nonce from the transactions' table to addresses' table in batches.

apps/explorer/priv/repo/migrations/20181106152300_add_nonce_to_addresses.exs

@@ -1,4 +1,13 @@
 defmodule Explorer.Repo.Migrations.AddNonceToAddresses do
+  @moduledoc """
+  Use `priv/repo/migrations/scripts/20181126182700_migrate_address_nonce.sql` to migrate data.
+
+  ```sh
+  mix ecto.migrate
+  psql -d $DATABASE -a -f priv/repo/migrations/scripts/20181126182700_migrate_address_nonce.sql
+  ```
+  """
+
   use Ecto.Migration
 
   def up do
@@ -6,20 +15,6 @@ defmodule Explorer.Repo.Migrations.AddNonceToAddresses do
     alter table(:addresses) do
       add(:nonce, :integer)
     end
-
-    # Populate nonce field from transactions table
-    # Commented out due to running time concerns
-    # execute("""
-    #     WITH t AS (
-    #         SELECT from_address_hash AS hash, MAX(nonce) AS nonce
-    #         FROM transactions
-    #         GROUP BY hash
-    #     )
-    #  UPDATE addresses AS a
-    #     SET nonce = t.nonce
-    #     FROM t
-    #     WHERE a.hash = t.hash
-    # """)
   end
 
   def down do

apps/explorer/priv/repo/migrations/scripts/20181126182700_migrate_address_nonce.sql

@@ -0,0 +1,55 @@
+DO $$
+ DECLARE
+    row_count integer := 1;
+    batch_size  integer := 50000; -- HOW MANY ITEMS WILL BE UPDATED AT TIME
+    iterator  integer := batch_size;
+    affected integer;
+ BEGIN
+   DROP TABLE IF EXISTS addresses_nonce_temp;
+
+   -- CREATES TEMP TABLE TO STORE THE ADDRESS NONCE TO BE UPDATED
+   CREATE TEMP TABLE addresses_nonce_temp(
+     from_address_hash bytea,
+     nonce integer,
+     row_number integer
+   );
+
+   INSERT INTO addresses_nonce_temp
+   SELECT DISTINCT ON (from_address_hash)
+     from_address_hash,
+     nonce,
+     ROW_NUMBER () OVER ()
+   FROM transactions
+   ORDER BY from_address_hash, nonce DESC;
+
+   row_count := (SELECT count(*) FROM addresses_nonce_temp);
+
+   RAISE NOTICE '% items to be updated', row_count;
+
+   -- ITERATES THROUGH THE ITEMS UNTIL THE TEMP TABLE IS EMPTY
+   WHILE row_count > 0 LOOP
+     -- UPDATES THE ADDRESS NONCE AND RETURNS THE ADDRESS_HASH
+     WITH updated_addresses AS (
+       UPDATE addresses SET nonce = addresses_nonce_temp.nonce
+       FROM addresses_nonce_temp
+       WHERE addresses_nonce_temp.from_address_hash = addresses.hash
+       AND addresses_nonce_temp.row_number <= iterator
+       RETURNING addresses_nonce_temp.from_address_hash
+     )
+     DELETE FROM addresses_nonce_temp
+     WHERE (from_address_hash) IN (select from_address_hash from updated_addresses);
+
+     GET DIAGNOSTICS affected = ROW_COUNT;
+     RAISE NOTICE '-> % addresses updated!', affected;
+
+     -- COMMITS THE BATCH UPDATES
+     CHECKPOINT;
+
+     -- UPDATES THE COUNTER SO IT DOESN'T TURN INTO A INFINITE LOOP
+     row_count := (SELECT count(*) FROM addresses_nonce_temp);
+     iterator := iterator + batch_size;
+
+     RAISE NOTICE '-> % counter', row_count;
+     RAISE NOTICE '-> % next batch', iterator;
+   END LOOP;
+ END $$;