maria-developers team mailing list archive

[Sergei Golubchik <serg@xxxxxxxxxxx>]

Hi, Nirbhay!

Just a couple of questions/comments, see below.

And please pay attention to Kristian's email about locking and parallel
replication. I don't think I can confidently review it in a patch, so
you may want to spend more time testing or analyzing that code.

Ok to push, when you're ready! Thanks!

On May 26, Nirbhay Choubey wrote:
> revision-id: 56a2835872c4ac7296ec0ae2ff618822855b0fc0 (mariadb-10.1.8-82-g56a2835)
> parent(s): 28c289626f318631d707f85b057a90af99018b06
> author: Nirbhay Choubey
> committer: Nirbhay Choubey
> timestamp: 2016-05-26 20:42:47 -0400
> message:
> 
> MDEV-5535: Cannot reopen temporary table
> 
> mysqld maintains a list of TABLE objects for all temporary
> tables in THD, where each table is represented by a TABLE
> object. A query referencing a temporary table for more than
> once, however, failed with ER_CANT_REOPEN_TABLE error.
 
"because a TABLE_SHARE was allocate together with the TABLE, so
temporary tables always had one TABLE per TABLE_SHARE"

> This patch lift this restriction by preserving the TABLE_SHARE
> object of each created temporary table, so that multiple instances
> of TABLE objects can be created.

better "by separating TABLE and TABLE_SHARE objects and storing
TABLE_SHARE's in the list in a THD, and TABLE's in the list in
the corresponding TABLE_SHARE"

> diff --git a/sql/rpl_rli.cc b/sql/rpl_rli.cc
> index 7bdd9c1..77f458b 100644
> --- a/sql/rpl_rli.cc
> +++ b/sql/rpl_rli.cc
> @@ -1060,24 +1061,43 @@ void Relay_log_info::inc_group_relay_log_pos(ulonglong log_pos,
>  
>  void Relay_log_info::close_temporary_tables()
>  {
> -  TABLE *table,*next;
>    DBUG_ENTER("Relay_log_info::close_temporary_tables");
>  
> -  for (table=save_temporary_tables ; table ; table=next)
> +  TMP_TABLE_SHARE *share;
> +  TABLE *table;
> +
> +  while ((share= save_temporary_tables.pop_front()))
>    {
> -    next=table->next;
> +    /*
> +      Iterate over the list of tables for this TABLE_SHARE and close them.
> +    */
> +    while ((table= share->all_tmp_tables.pop_front()))
> +    {
> +      DBUG_PRINT("tmptable", ("closing table: '%s'.'%s'",
> +                              table->s->db.str, table->s->table_name.str));
> +
> +      /* Reset in_use as the table may have been created by another thd */
> +      table->in_use= 0;
> +      free_io_cache(table);
> +      /*
> +        Lets not free TABLE_SHARE here as there could be multiple TABLEs opened
> +        for the same table (TABLE_SHARE).
> +      */
> +      closefrm(table, false);
> +      my_free(table);
> +    }
>  
> -    /* Reset in_use as the table may have been created by another thd */
> -    table->in_use=0;
>      /*
>        Don't ask for disk deletion. For now, anyway they will be deleted when
>        slave restarts, but it is a better intention to not delete them.
>      */
> -    DBUG_PRINT("info", ("table: 0x%lx", (long) table));
> -    close_temporary(table, 1, 0);
> +
> +    free_table_share(share);
> +    my_free(share);
>    }
> -  save_temporary_tables= 0;
> -  slave_open_temp_tables= 0;
> +
> +  save_temporary_tables.empty();

Is it needed?
you've popped all shares from the list, it's empty.
I'd rather add an assert instead

> +
>    DBUG_VOID_RETURN;
>  }
>  
> diff --git a/sql/sql_class.h b/sql/sql_class.h
> index ae240ae..a70c4a9 100644
> --- a/sql/sql_class.h
> +++ b/sql/sql_class.h
> @@ -1247,6 +1247,61 @@ enum enum_locked_tables_mode
>    LTM_PRELOCKED_UNDER_LOCK_TABLES
>  };
>  
> +/**
> +  The following structure is an extension to TABLE_SHARE and is
> +  exclusively for temporary tables.
> +
> +  @note:
> +  Although, TDC_element has data members (like next, prev &
> +  all_tables) to store the list of TABLE_SHARE & TABLE objects
> +  related to a particular TABLE_SHARE, they cannot be moved to
> +  TABLE_SHARE in order to be reused for temporary tables. This
> +  is because, as concurrent threads iterating through hash of
> +  TDC_element's may need access to all_tables, but if all_tables
> +  is made part of TABLE_SHARE, then TDC_element->share->all_tables
> +  is not always guaranteed to be valid, as TDC_element can live
> +  longer than TABLE_SHARE.
> +*/
> +struct TMP_TABLE_SHARE : public TABLE_SHARE
> +{
> +private:
> +  /*
> +   Link to all temporary table shares. Declared as private to
> +   avoid direct manipulation with those objects. One should
> +   use methods of I_P_List template instead.
> +  */
> +  TMP_TABLE_SHARE *tmp_next;
> +  TMP_TABLE_SHARE **tmp_prev;
> +
> +  friend struct All_tmp_table_shares;
> +
> +public:
> +  /*
> +    Doubly-linked (back-linked) lists of used and unused TABLE objects
> +    for this share.

and unused? you don't free them but keep in the list?

> +  */
> +  All_share_tables_list all_tmp_tables;
> +};
> +
> +/**
> +  Helper class which specifies which members of TMP_TABLE_SHARE are
> +  used for participation in the list of temporary tables.
> +*/
> +
> +struct All_tmp_table_shares
> +{
> +  static inline TMP_TABLE_SHARE **next_ptr(TMP_TABLE_SHARE *l)
> +  {
> +    return &l->tmp_next;
> +  }
> +  static inline TMP_TABLE_SHARE ***prev_ptr(TMP_TABLE_SHARE *l)
> +  {
> +    return &l->tmp_prev;
> +  }
> +};
> +
> +/* Also used in rpl_rli.h. */
> +typedef I_P_List <TMP_TABLE_SHARE, All_tmp_table_shares> All_tmp_tables_list;
>  
>  /**
>    Class that holds information about tables which were opened and locked
> diff --git a/sql/temporary_tables.cc b/sql/temporary_tables.cc
> new file mode 100644
> index 0000000..1514b72
> --- /dev/null
> +++ b/sql/temporary_tables.cc
...
> +TABLE *THD::find_temporary_table(const char *db,
> +                                 const char *table_name)
> +{
> +  DBUG_ENTER("THD::find_temporary_table");
> +
> +  TABLE *table;
> +  char key[MAX_DBKEY_LENGTH];
> +  uint key_length;
> +  bool locked;
> +
> +  if (!(has_temporary_tables() || (rgi_slave && has_slave_temporary_tables())))

hmm, really? you had here is_empty(true) before
and your is_empty() was working like this:

  if (flag_is_true)
  { do rgi_slave }
  else
  { do thd }

your old is_empty was not checking thd if the argument was true,
your new code does, as if your is_empty() was

  do thd;
  if (flag_is_true)
  { do rgi_slave}

> +  {
> +    DBUG_RETURN(NULL);
> +  }
> +
> +  key_length= create_tmp_table_def_key(key, db, table_name);

Regards,
Sergei
Chief Architect MariaDB
and security@xxxxxxxxxxx