Add script to validate internal_transactions constraint for large DBs

Problem: executing the existing sql script to validate internal_transactions constraint is too slow (or even gets stuck) for large DBs and its progress cannot be checked.

Solution: add an alternative implementation of the same script that can be monitored from outside and has better performance.

CHANGELOG.md

@@ -1,6 +1,7 @@
 ## Current
 
 ### Features
+- [#2373](https://github.com/poanetwork/blockscout/pull/2373) - Add script to validate internal_transactions constraint for large DBs
 
 ### Fixes
 - [#2425](https://github.com/poanetwork/blockscout/pull/2425) - Force to show address view for checksummed address even if it is not in DB

apps/explorer/priv/repo/migrations/20181108205650_additional_internal_transaction_constraints.exs

@@ -7,6 +7,9 @@ defmodule Explorer.Repo.Migrations.AdditionalInternalTransactionConstraints do
   mix ecto.migrate
   psql -d $DATABASE -a -f priv/repo/migrations/scripts/20181108205650_additional_internal_transaction_constraints.sql
   ```
+
+  NOTE: you may want to consider using `apps/explorer/priv/repo/migrations/scripts/20181108205650_large_additional_internal_transaction_constraints.sql`
+  instead if you are dealing with a very large number of transactions/internal_transactions.
   """
 
   use Ecto.Migration

apps/explorer/priv/repo/migrations/scripts/20181108205650_large_additional_internal_transaction_constraints.sql

@@ -0,0 +1,75 @@
+-- This script is a reimplementation of `20181108205650_additional_internal_transaction_constraints.sql`
+-- that is meant to be executed on DBs where the number of transactions and/or
+-- internal_transactions is very large.
+-- To check the progress it is advised to run this in a `tmux` session or save
+-- the output to a file.
+-- IMPORTANT NOTE: after making all the corrections needed the script will NOT
+-- run the constraint validations because this may be a very long and taxing
+-- operation. To validate the constraint one can run, after the script fininshed:
+
+-- ALTER TABLE internal_transactions VALIDATE CONSTRAINT call_has_call_type;
+-- ALTER TABLE internal_transactions VALIDATE CONSTRAINT call_has_input;
+-- ALTER TABLE internal_transactions VALIDATE CONSTRAINT create_has_init;
+
+DO $$
+DECLARE
+   batch_size  integer := 10000; -- HOW MANY ITEMS WILL BE UPDATED AT A TIME
+   last_transaction_hash bytea; -- WILL CHECK ONLY TRANSACTIONS FOLLOWING THIS HASH (DESC)
+   last_fetched_batch_size integer;
+BEGIN
+  RAISE NOTICE 'STARTING SCRIPT';
+  CREATE TEMP TABLE transactions_with_deprecated_internal_transactions(hash bytea NOT NULL);
+
+  LOOP
+    RAISE NOTICE 'Fetching new batch of % transactions to correct', batch_size;
+
+    INSERT INTO transactions_with_deprecated_internal_transactions
+    SELECT DISTINCT transaction_hash
+    FROM internal_transactions
+    WHERE
+      (last_transaction_hash IS NULL OR transaction_hash < last_transaction_hash) AND
+      -- call_has_call_type CONSTRAINT
+      ((type = 'call' AND call_type IS NULL) OR
+      -- call_has_input CONSTRAINT
+      (type = 'call' AND input IS NULL) OR
+      -- create_has_init CONSTRAINT
+      (type = 'create' AND init is NULL))
+    ORDER BY transaction_hash DESC LIMIT batch_size;
+
+    SELECT INTO last_fetched_batch_size count(*) FROM transactions_with_deprecated_internal_transactions;
+
+    RAISE NOTICE 'Batch of % transactions was fetched, starting their deprecation', last_fetched_batch_size;
+
+    -- UPDATE TRANSACTIONS
+    UPDATE transactions
+    SET internal_transactions_indexed_at = NULL,
+        error = NULL
+    FROM transactions_with_deprecated_internal_transactions
+    WHERE transactions.hash = transactions_with_deprecated_internal_transactions.hash;
+
+    -- REMOVE THE DEPRECATED internal_transactions
+    DELETE FROM internal_transactions
+    USING transactions_with_deprecated_internal_transactions
+    WHERE internal_transactions.transaction_hash = transactions_with_deprecated_internal_transactions.hash;
+
+    -- COMMIT THE BATCH UPDATES
+    CHECKPOINT;
+
+    -- UPDATE last_transaction_hash TO KEEP TRACK OF ROWS ALREADY CHECKED
+    SELECT INTO last_transaction_hash hash
+    FROM transactions_with_deprecated_internal_transactions
+    ORDER BY hash ASC LIMIT 1;
+
+    RAISE NOTICE 'Last batch completed, last transaction hash: %', last_transaction_hash;
+
+    -- CLEAR THE TEMP TABLE
+    DELETE FROM transactions_with_deprecated_internal_transactions;
+
+    -- EXIT IF ALL internal_transactions HAVE BEEN CHECKED ALREADY
+    EXIT WHEN last_fetched_batch_size != batch_size;
+  END LOOP;
+
+  RAISE NOTICE 'SCRIPT FINISHED, all affected transactions have been deprecated';
+
+  DROP TABLE transactions_with_deprecated_internal_transactions;
+END $$;