Bug #117044 Builder::finish forgets to record MLOG_INDEX_LOAD for DDL need rebuild table

• Submitted: 25 Dec 2024 8:49
• Modified: 26 Dec 2024 6:41
• Reporter: George Ma (OCA)
• Status: Verified
• Category: MySQL Server: DDL
• Severity: S3 (Non-critical)
• Version: 8.0.40
• OS: Any
• CPU Architecture: Any
• Tags: Backup

[25 Dec 2024 8:49] George Ma

Description:
In 5.7 and 8.0, no redo log is written during DDL progress, and it need to flush the dirty pages and write a MLOG_INDEX_LOAD redo log before finish the DDL. (WL#7277, https://dev.mysql.com/worklog/task/?id=7277)

WL#14283 introduces the Parallel DDL, and the above steps are put into Builder::finish.

```
dberr_t Builder::finish() noexcept {
  if (get_error() != DB_SUCCESS) {
    set_next_state();
    return get_error();
  }

  ut_a(m_n_sort_tasks == 0);
  ut_a(get_state() == State::FINISH);

  for (auto thread_ctx : m_thread_ctxs) {
    thread_ctx->m_file.m_file.close();
  }

  dberr_t err{DB_SUCCESS};

  if (get_error() != DB_SUCCESS || !m_ctx.m_online) {
    /* Do not apply any online log. */
  } else if (m_ctx.m_old_table != m_ctx.m_new_table) {
    ut_a(!m_index->online_log);
    ut_a(m_index->online_status == ONLINE_INDEX_COMPLETE);

    auto observer = m_ctx.m_trx->flush_observer;
    observer->flush();

  } else {
    err = finalize();

    if (err != DB_SUCCESS) {
      set_error(err);
    }
  }

  set_next_state();

  return get_error();
}
```

But I found that if the DDL do not need to rebuild table, it will call finalize and it will call write_redo inside. But if the DDL need to rebuild table(like OPTIMIZE TABLE), it will call `observer->flush` only, which forgets to record MLOG_INDEX_LOAD.

This will not affect the correctness of the data, but it may lead to failures in the backup(Xtrabackup).

How to repeat:
No need.

Suggested fix:
@@ -2066,6 +2067,7 @@ dberr_t Builder::finish() noexcept {
     auto observer = m_ctx.m_trx->flush_observer;
     observer->flush();

+    write_redo(m_index);
   } else {
     err = finalize();

[26 Dec 2024 6:41] MySQL Verification Team

Hello George Ma,

Thank you for the report and feedback.

regards,
Umesh

[22 Jul 8:05] Ke Yu

Not a bug.

The MLOG_INDEX_LOAD will be recored by Context::cleanup() function for DDL need rebuild table. The code is :

```
dberr_t Context::cleanup(dberr_t err) noexcept {
...
      for (auto index = first_index; index != nullptr; index = index->next()) {
        if (m_old_table != m_new_table) {
          // write MLOG_INDEX_LOAD
          Builder::write_redo(index);
        }
      }
...
}