BUG#24818604: MYSQLD CRASHES WHILE STARTING GROUP REPLICATION FOR A NODE IN RECOVERY PROCESS

During BUG#24818604: MYSQLD CRASHES WHILE STARTING GROUP REPLICATION
FOR A NODE IN RECOVERY PROCESS analysis, three issues were found:
 1) Foreign keys were not being ignored when foreign_key_checks == 0
    That was fixed on BUG#24916351: GR KEY GENERATION FOR FOREIGN
    KEY SHOULD BE IGNORED IF PARENT IS NOT YET CREATED
 2) Foreign keys referenced_key_name could be NULL when a DELETE on
    a child table was executed before accessing the parent, like
    just after server start.
    That was fixed on BUG#25126722 FOREIGN KEY CONSTRAINT NAME IS
    NULL IN INFORMATION_SCHEMA AFTER RESTART
 3) A DELETE on child table after the parent table was dropped using
    foreign_key_checks= 0, is making referenced_key_name NULL and
    consequently crashing the server.

This patch solves issue 3), by skipping foreign keys inclusion on
transaction write set if referenced_key_name is NULL, since this,
after issue 1) and 2) fix, means that the parent table does not
exist and there is no foreign key constraint.

(cherry picked from commit 3160ccf71a0b6fd1d5d87d4ce63c9477f5626e44)

Author: nacarvalho

mysql-test/suite/binlog/r/binlog_foreign_key_parent_table_deleted.result

@@ -0,0 +1,13 @@
+call mtr.add_suppression("InnoDB: Foreign Key referenced table test.t1 not found for foreign table test.t2");
+SET @saved_foreign_key_checks= @@session.foreign_key_checks;
+SET @@session.foreign_key_checks= 1;
+CREATE TABLE t1 (c1 INT PRIMARY KEY);
+CREATE TABLE t2 (c1 INT PRIMARY KEY, FOREIGN KEY (c1) REFERENCES t1(c1));
+INSERT INTO t1 VALUES (1);
+INSERT INTO t2 VALUES (1);
+SET @@session.foreign_key_checks= 0;
+DROP TABLE t1;
+SET @@session.foreign_key_checks= 1;
+DELETE FROM t2 WHERE c1=1;
+DROP TABLE t2;
+SET @@session.foreign_key_checks= @saved_foreign_key_checks;

mysql-test/suite/binlog/t/binlog_foreign_key_parent_table_deleted-master.opt

@@ -0,0 +1 @@
+--transaction-write-set-extraction=XXHASH64

mysql-test/suite/binlog/t/binlog_foreign_key_parent_table_deleted.test

@@ -0,0 +1,31 @@
+################################################################################
+# Validate that when a DELETE operation is done on a child table, after the
+# parent table was dropped using foreign_key_checks= 0, the server does not crash.
+#
+# Test:
+# 0. Create a parent and child tables.
+# 1. Drop parent table with foreign_key_checks= 0.
+# 2. Delete a row from the child table with foreign_key_checks= 1.
+################################################################################
+--source include/have_binlog_format_row.inc
+
+call mtr.add_suppression("InnoDB: Foreign Key referenced table test.t1 not found for foreign table test.t2");
+
+SET @saved_foreign_key_checks= @@session.foreign_key_checks;
+SET @@session.foreign_key_checks= 1;
+
+CREATE TABLE t1 (c1 INT PRIMARY KEY);
+CREATE TABLE t2 (c1 INT PRIMARY KEY, FOREIGN KEY (c1) REFERENCES t1(c1));
+
+INSERT INTO t1 VALUES (1);
+INSERT INTO t2 VALUES (1);
+
+SET @@session.foreign_key_checks= 0;
+DROP TABLE t1;
+SET @@session.foreign_key_checks= 1;
+
+DELETE FROM t2 WHERE c1=1;
+
+DROP TABLE t2;
+
+SET @@session.foreign_key_checks= @saved_foreign_key_checks;

sql/rpl_write_set_handler.cc

@@ -106,6 +106,14 @@ void check_foreign_key(TABLE *table, THD *thd,
   LEX_STRING *f_info;
   while ((f_key_info=foreign_key_iterator++))
   {
+    /*
+      If referenced_key_name is NULL it means that the parent table
+      was dropped using foreign_key_checks= 0, on that case we
+      cannot check foreign key and need to skip it.
+    */
+    if (f_key_info->referenced_key_name == NULL)
+      continue;
+
     std::string temporary_pke;
     List_iterator_fast<LEX_STRING> foreign_fields_iterator(f_key_info->foreign_fields);
 
@@ -125,7 +133,6 @@ void check_foreign_key(TABLE *table, THD *thd,
                                 length_table, MYF(0));
     char *char_length_table= my_safe_itoa(10, length_table, &buffer_table[length_table-1]);
 
-    DBUG_ASSERT(f_key_info->referenced_key_name);
     /*
       Prefix the hash keys with the referenced index name.
     */