don't bother unnecessarily setting max_update_limit

avoids 1 to 3 extra db round trips if we're already doing batches
of 1000

Change-Id: I0b17a1072ad0a54c01ba0b9778f94bf3255ef014
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/338146
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Jacob Burroughs <jburroughs@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
Migration-Review: Cody Cutrer <cody@instructure.com>

config/initializers/postgresql_adapter.rb

@@ -23,6 +23,14 @@ class QuotedValue < String
 end
 
 module PostgreSQLAdapterExtensions
+  # when changing this, you need to re-apply the latest migration creating the guard_excessive_updates function
+  DEFAULT_MAX_UPDATE_LIMIT = 1000
+
+  def initialize(*)
+    super
+    @max_update_limit = DEFAULT_MAX_UPDATE_LIMIT
+  end
+
   def configure_connection
     super
 
@@ -258,6 +266,11 @@ module PostgreSQLAdapterExtensions
   end
 
   def with_max_update_limit(limit)
+    return yield if limit == @max_update_limit
+
+    old_limit = @max_update_limit
+    @max_update_limit = limit
+
     if transaction_open?
       execute("SET LOCAL inst.max_update_limit = #{limit}")
       ret = yield
@@ -269,6 +282,8 @@ module PostgreSQLAdapterExtensions
       end
     end
     ret
+  ensure
+    @max_update_limit = old_limit if old_limit
   end
 
   def quote(*args)

db/migrate/20230222192524_guard_excessive_updates.rb

@@ -55,7 +55,7 @@ class GuardExcessiveUpdates < ActiveRecord::Migration[7.0]
           max_record_count integer;
       BEGIN
           SELECT count(*) FROM oldtbl INTO record_count;
-          max_record_count := COALESCE(setting_as_int('inst.max_update_limit.' || TG_TABLE_NAME), setting_as_int('inst.max_update_limit'), '1000');
+          max_record_count := COALESCE(setting_as_int('inst.max_update_limit.' || TG_TABLE_NAME), setting_as_int('inst.max_update_limit'), '#{PostgreSQLAdapterExtensions::DEFAULT_MAX_UPDATE_LIMIT}');
           IF record_count > max_record_count THEN
               IF current_setting('inst.max_update_fail', true) IS NOT DISTINCT FROM 'true' THEN
                   RAISE EXCEPTION 'guard_excessive_updates: % to %.% failed. Would update % records but max is %', TG_OP, TG_TABLE_SCHEMA, TG_TABLE_NAME, record_count, max_record_count;

db/migrate/20230317213850_better_guard_logs.rb

@@ -29,7 +29,7 @@ class BetterGuardLogs < ActiveRecord::Migration[7.0]
           max_record_count integer;
       BEGIN
           SELECT count(*) FROM oldtbl INTO record_count;
-          max_record_count := COALESCE(setting_as_int('inst.max_update_limit.' || TG_TABLE_NAME), setting_as_int('inst.max_update_limit'), '1000');
+          max_record_count := COALESCE(setting_as_int('inst.max_update_limit.' || TG_TABLE_NAME), setting_as_int('inst.max_update_limit'), '#{PostgreSQLAdapterExtensions::DEFAULT_MAX_UPDATE_LIMIT}');
           IF record_count > max_record_count THEN
             IF current_setting('inst.max_update_fail', true) IS NOT DISTINCT FROM 'true' THEN
                 RAISE EXCEPTION 'guard_excessive_updates: % to %.% failed', TG_OP, TG_TABLE_SCHEMA, TG_TABLE_NAME USING DETAIL = 'Would update ' || record_count || ' records but max is ' || max_record_count;
@@ -52,7 +52,7 @@ class BetterGuardLogs < ActiveRecord::Migration[7.0]
           max_record_count integer;
       BEGIN
           SELECT count(*) FROM oldtbl INTO record_count;
-          max_record_count := COALESCE(setting_as_int('inst.max_update_limit.' || TG_TABLE_NAME), setting_as_int('inst.max_update_limit'), '1000');
+          max_record_count := COALESCE(setting_as_int('inst.max_update_limit.' || TG_TABLE_NAME), setting_as_int('inst.max_update_limit'), '#{PostgreSQLAdapterExtensions::DEFAULT_MAX_UPDATE_LIMIT}');
           IF record_count > max_record_count THEN
               IF current_setting('inst.max_update_fail', true) IS NOT DISTINCT FROM 'true' THEN
                   RAISE EXCEPTION 'guard_excessive_updates: % to %.% failed. Would update % records but max is %', TG_OP, TG_TABLE_SCHEMA, TG_TABLE_NAME, record_count, max_record_count;

db/migrate/20230330125148_even_better_guard_logs.rb

@@ -29,7 +29,7 @@ class EvenBetterGuardLogs < ActiveRecord::Migration[7.0]
           max_record_count integer;
       BEGIN
           SELECT count(*) FROM oldtbl INTO record_count;
-          max_record_count := COALESCE(setting_as_int('inst.max_update_limit.' || TG_TABLE_NAME), setting_as_int('inst.max_update_limit'), '1000');
+          max_record_count := COALESCE(setting_as_int('inst.max_update_limit.' || TG_TABLE_NAME), setting_as_int('inst.max_update_limit'), '#{PostgreSQLAdapterExtensions::DEFAULT_MAX_UPDATE_LIMIT}');
           IF record_count > max_record_count THEN
             IF current_setting('inst.max_update_fail', true) IS NOT DISTINCT FROM 'true' THEN
                 RAISE EXCEPTION 'guard_excessive_updates: % to %.% failed', TG_OP, TG_TABLE_SCHEMA, TG_TABLE_NAME USING DETAIL = 'Would update ' || record_count || ' records but max is ' || max_record_count || ', orig query: ' || current_query();
@@ -52,7 +52,7 @@ class EvenBetterGuardLogs < ActiveRecord::Migration[7.0]
           max_record_count integer;
       BEGIN
           SELECT count(*) FROM oldtbl INTO record_count;
-          max_record_count := COALESCE(setting_as_int('inst.max_update_limit.' || TG_TABLE_NAME), setting_as_int('inst.max_update_limit'), '1000');
+          max_record_count := COALESCE(setting_as_int('inst.max_update_limit.' || TG_TABLE_NAME), setting_as_int('inst.max_update_limit'), '#{PostgreSQLAdapterExtensions::DEFAULT_MAX_UPDATE_LIMIT}');
           IF record_count > max_record_count THEN
             IF current_setting('inst.max_update_fail', true) IS NOT DISTINCT FROM 'true' THEN
                 RAISE EXCEPTION 'guard_excessive_updates: % to %.% failed', TG_OP, TG_TABLE_SCHEMA, TG_TABLE_NAME USING DETAIL = 'Would update ' || record_count || ' records but max is ' || max_record_count;