MDEV-37602: Phase 1 & 2 - Session-scoped rgi and Master_info registration in index

[bodyhedia44]

Phase 1: Persist rpl_group_info per connection instead of per BINLOG statement
Phase 2: Create session Master_info and register in master_info_index with unique names

[gemini-code-assist]

Code Review

This pull request introduces a session-scoped Master_info (mi_fake) for BINLOG replay statements to eliminate the overhead of creating and deleting throwaway Master_info instances per query event. The session-scoped instance is registered in master_info_index and cleaned up during connection teardown. Feedback highlights two critical issues: first, master_info_index can be NULL on standalone servers and its modification requires holding the LOCK_active_mi mutex to avoid race conditions; second, the allocation of rpl_group_info lacks a NULL check, which could lead to a server crash if memory is exhausted.

[gemini-code-assist]

The global master_info_index can be NULL on standalone servers where replication is not initialized or disabled. Dereferencing it directly will cause a server crash when executing BINLOG statements. Additionally, modifying master_info_index requires holding the LOCK_active_mi mutex to prevent race conditions with other threads (e.g., concurrent SHOW STATUS or administrative commands).

Please add a NULL check for master_info_index and wrap the registration in LOCK_active_mi.

    if (master_info_index)
    {
      mysql_mutex_lock(&LOCK_active_mi);
      if (master_info_index->add_master_info(mi, FALSE))
      {
        mysql_mutex_unlock(&LOCK_active_mi);
        delete mi;
        my_error(ER_OUTOFMEMORY, MYF(ME_FATAL), 1);
        goto end;
      }
      mysql_mutex_unlock(&LOCK_active_mi);
    }

[gemini-code-assist]

If new rpl_group_info(rli) fails and returns NULL due to an out-of-memory condition, dereferencing rgi on the next line (rgi->thd = thd;) will cause a server crash. We should check if rgi is NULL and handle the error gracefully.

  if (!rgi)
  {
    if (!(rgi= thd->rgi_fake= new rpl_group_info(rli)))
    {
      my_error(ER_OUTOFMEMORY, MYF(ME_FATAL), 1);
      goto end;
    }
  }
  rgi->thd= thd;