MDEV-15304: Server crash in print_keydup_error / key_unpack or unexpected ER_DUP_KEY

Fix two issues:
1. Rdb_ddl_manager::rename() loses the value of m_hidden_pk_val. new
object used to get 0, which means "not loaded from the db yet".

2. ha_rocksdb::load_hidden_pk_value() uses current transaction (and its
snapshot) when loading hidden PK value from disk. This may cause it to
load an out-of-date value.

storage/rocksdb/ha_rocksdb.cc

@@ -5235,8 +5235,17 @@ int ha_rocksdb::load_hidden_pk_value() {
   active_index = m_tbl_def->m_key_count - 1;
   const uint8 save_table_status = table->status;
 
-  Rdb_transaction *const tx = get_or_create_tx(table->in_use);
+  /*
-  const bool is_new_snapshot = !tx->has_snapshot();
+    We should read the latest committed value in the database.
+    That is, if we have an open transaction with a snapshot, we should not use
+    it as we may get old data. Start a new transaction to read the latest
+    value.
+  */
+  Rdb_transaction *const temp_tx = new Rdb_transaction_impl(table->in_use);
+  temp_tx->start_tx();
+  Rdb_transaction *&tx = get_tx_from_thd(table->in_use);
+  Rdb_transaction *save_tx= tx;
+  tx= temp_tx;
 
   longlong hidden_pk_id = 1;
   // Do a lookup.
@@ -5246,9 +5255,8 @@ int ha_rocksdb::load_hidden_pk_value() {
     */
     auto err = read_hidden_pk_id_from_rowkey(&hidden_pk_id);
     if (err) {
-      if (is_new_snapshot) {
+        delete tx;
-        tx->release_snapshot();
+        tx= save_tx;
-      }
       return err;
     }
 
@@ -5260,9 +5268,8 @@ int ha_rocksdb::load_hidden_pk_value() {
          !m_tbl_def->m_hidden_pk_val.compare_exchange_weak(old, hidden_pk_id)) {
   }
 
-  if (is_new_snapshot) {
+  delete tx;
-    tx->release_snapshot();
+  tx= save_tx;
-  }
 
   table->status = save_table_status;
   active_index = save_active_index;

storage/rocksdb/mysql-test/rocksdb/r/allow_no_primary_key.result

@@ -262,3 +262,34 @@ SELECT * FROM t1;
 a	b
 36	foo
 DROP TABLE t1;
+#
+# Issue #834/MDEV-15304 ALTER TABLE table_with_hidden_pk causes Can't
+#   write; duplicate key in table error and/or crash
+#
+CREATE TABLE t1 (a INT, KEY(a)) ENGINE=RocksDB;
+INSERT INTO t1 VALUES (1),(1+1);
+create table t2 (a int);
+insert into t2 values (10),(20),(30);
+BEGIN;
+select * from t2;
+a
+10
+20
+30
+connect  con1,localhost,root,,;
+connection con1;
+alter table t1 force;
+connection default;
+select * from t1;
+a
+connection con1;
+insert into t1 values (100);
+select * from t1;
+a
+1
+2
+100
+disconnect con1;
+connection default;
+rollback;
+drop table t1,t2;

storage/rocksdb/mysql-test/rocksdb/t/allow_no_primary_key.test

@@ -96,3 +96,31 @@ DELETE FROM t1 WHERE a = 35 AND b = 'foo';
 --sorted_result
 SELECT * FROM t1;
 DROP TABLE t1;
+
+--echo #
+--echo # Issue #834/MDEV-15304 ALTER TABLE table_with_hidden_pk causes Can't
+--echo #   write; duplicate key in table error and/or crash
+--echo #
+CREATE TABLE t1 (a INT, KEY(a)) ENGINE=RocksDB;
+INSERT INTO t1 VALUES (1),(1+1);
+create table t2 (a int);
+insert into t2 values (10),(20),(30);
+
+BEGIN;
+select * from t2;
+
+connect (con1,localhost,root,,);
+connection con1;
+alter table t1 force;
+
+connection default;
+select * from t1;
+
+connection con1;
+insert into t1 values (100);
+select * from t1;
+
+disconnect con1;
+connection default;
+rollback;
+drop table t1,t2;

storage/rocksdb/rdb_datadic.cc

@@ -4271,6 +4271,9 @@ bool Rdb_ddl_manager::rename(const std::string &from, const std::string &to,
       rec->m_auto_incr_val.load(std::memory_order_relaxed);
   new_rec->m_key_descr_arr = rec->m_key_descr_arr;
 
+  new_rec->m_hidden_pk_val =
+      rec->m_hidden_pk_val.load(std::memory_order_relaxed);
+
   // so that it's not free'd when deleting the old rec
   rec->m_key_descr_arr = nullptr;