MDEV-37990: redundant Table map events in binlog

[plampio]

This patch modifies how a Galera slave node writes Table map events to binary log. Now a Galera slave does not write duplicate Table Map events to binary log.

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[gemini-code-assist]

Code Review

This pull request addresses MDEV-37990 by preventing redundant Table_map events in the binary log during Galera replication. It introduces a mechanism in the THD class to track mapped tables within a transaction. The review feedback identifies several areas for improvement: correcting MariaDB coding style and return types in sql/log.cc, fixing a regex bug in the test script that prevents correct transaction boundary detection, and suggesting the use of a more lightweight container than std::unordered_set in the core sql_class.h header to optimize performance and compilation times.

[gemini-code-assist]

The indentation and brace placement in this block do not follow the MariaDB coding style. The block inside the if statement should be indented by 2 spaces relative to the if, and the opening brace { is typically placed on a new line. Additionally, for a function returning bool, false is more idiomatic than 0 to indicate success.

#ifdef WITH_WSREP
  if (wsrep_thd_is_applying(this) &&
      !wsrep_mark_table_mapped(table->s->table_map_id))
  {
    /* A table map event for this table is already recorded for this
       transaction, skip writing the table map event. */
    DBUG_RETURN(false);
  }
#endif

References

1. MariaDB coding style: 2-space indentation, opening braces on a new line for blocks, and use 'false' for boolean success in functions returning bool. ^(link)

[gemini-code-assist]

The regex /^(?:COMMIT|Xid =)/ is anchored to the start of the line, but Xid = in mysqlbinlog output is typically preceded by metadata and a tab. This will prevent the regex from correctly identifying transaction boundaries for XID events. Removing the ^ anchor will allow it to match correctly.

      $xid++ if $line =~ /COMMIT|Xid =/;

[gemini-code-assist]

Including <unordered_set> in a core header like sql_class.h can increase compilation times. Additionally, std::unordered_set is relatively heavy for tracking a small number of tables. Consider using a more lightweight container like Prealloced_array or std::vector with linear search, which would be more efficient for the typical case and avoid unnecessary heap allocations.