path: root/sql/sql_cursor.cc

/* Copyright (C) 2005-2006 MySQL AB

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; version 2 of the License.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */
#ifdef USE_PRAGMA_IMPLEMENTATION
#pragma implementation                         /* gcc class implementation */
#endif

#include "sql_priv.h"
#include "unireg.h"
#include "sql_cursor.h"
#include "probes_mysql.h"
#include "sql_parse.h"                        // mysql_execute_command

/****************************************************************************
  Declarations.
****************************************************************************/

/**
  Materialized_cursor -- an insensitive materialized server-side
  cursor. The result set of this cursor is saved in a temporary
  table at open. The cursor itself is simply an interface for the
  handler of the temporary table.
*/

class Materialized_cursor: public Server_side_cursor
{
  MEM_ROOT main_mem_root;
  /* A fake unit to supply to select_send when fetching */
  SELECT_LEX_UNIT fake_unit;
  TABLE *table;
  List<Item> item_list;
  ulong fetch_limit;
  ulong fetch_count;
  bool is_rnd_inited;
public:
  Materialized_cursor(select_result *result, TABLE *table);

  int fill_item_list(THD *thd, List<Item> &send_result_set_metadata);
  virtual bool is_open() const { return table != 0; }
  virtual int open(JOIN *join __attribute__((unused)));
  virtual void fetch(ulong num_rows);
  virtual void close();
  virtual ~Materialized_cursor();
};


/**
  Select_materialize -- a mediator between a cursor query and the
  protocol. In case we were not able to open a non-materialzed
  cursor, it creates an internal temporary HEAP table, and insert
  all rows into it. When the table reaches max_heap_table_size,
  it's converted to a MyISAM table. Later this table is used to
  create a Materialized_cursor.
*/

class Select_materialize: public select_union
{
  select_result *result; /**< the result object of the caller (PS or SP) */
public:
  Materialized_cursor *materialized_cursor;
  Select_materialize(select_result *result_arg)
    :result(result_arg), materialized_cursor(0) {}
  virtual bool send_result_set_metadata(List<Item> &list, uint flags);
};


/**************************************************************************/

/**
  Attempt to open a materialized cursor.

  @param      thd           thread handle
  @param[in]  result        result class of the caller used as a destination
                            for the rows fetched from the cursor
  @param[out] pcursor       a pointer to store a pointer to cursor in

  @retval
    0                 the query has been successfully executed; in this
    case pcursor may or may not contain
    a pointer to an open cursor.
  @retval
    non-zero          an error, 'pcursor' has been left intact.
*/

int mysql_open_cursor(THD *thd, select_result *result,
                      Server_side_cursor **pcursor)
{
  select_result *save_result;
  Select_materialize *result_materialize;
  LEX *lex= thd->lex;
  int rc;

  if (! (result_materialize= new (thd->mem_root) Select_materialize(result)))
    return 1;

  save_result= lex->result;

  lex->result= result_materialize;

  MYSQL_QUERY_EXEC_START(thd->query(),
                         thd->thread_id,
                         (char *) (thd->db ? thd->db : ""),
                         thd->security_ctx->priv_user,
                         (char *) thd->security_ctx->host_or_ip,
                         2);
  rc= mysql_execute_command(thd);
  MYSQL_QUERY_EXEC_DONE(rc);

  lex->result= save_result;
  /*
    Possible options here:
    - a materialized cursor is open. In this case rc is 0 and
      result_materialize->materialized is not NULL
    - an error occurred during materialization.
      result_materialize->materialized_cursor is not NULL, but rc != 0
    - successful completion of mysql_execute_command without
      a cursor: rc is 0, result_materialize->materialized_cursor is NULL.
      This is possible if some command writes directly to the
      network, bypassing select_result mechanism. An example of
      such command is SHOW VARIABLES or SHOW STATUS.
  */
  if (rc)
  {
    if (result_materialize->materialized_cursor)
      delete result_materialize->materialized_cursor;
    goto end;
  }

  if (result_materialize->materialized_cursor)
  {
    Materialized_cursor *materialized_cursor=
      result_materialize->materialized_cursor;

    if ((rc= materialized_cursor->open(0)))
    {
      delete materialized_cursor;
      goto end;
    }

    *pcursor= materialized_cursor;
    thd->stmt_arena->cleanup_stmt();
  }

end:
  delete result_materialize;
  return rc;
}

/****************************************************************************
  Server_side_cursor
****************************************************************************/

Server_side_cursor::~Server_side_cursor()
{
}


void Server_side_cursor::operator delete(void *ptr, size_t size)
{
  Server_side_cursor *cursor= (Server_side_cursor*) ptr;
  MEM_ROOT own_root= *cursor->mem_root;

  DBUG_ENTER("Server_side_cursor::operator delete");
  TRASH(ptr, size);
  /*
    If this cursor has never been opened mem_root is empty. Otherwise
    mem_root points to the memory the cursor object was allocated in.
    In this case it's important to call free_root last, and free a copy
    instead of *mem_root to avoid writing into freed memory.
  */
  free_root(&own_root, MYF(0));
  DBUG_VOID_RETURN;
}


/***************************************************************************
 Materialized_cursor
****************************************************************************/

Materialized_cursor::Materialized_cursor(select_result *result_arg,
                                         TABLE *table_arg)
  :Server_side_cursor(&table_arg->mem_root, result_arg),
  table(table_arg),
  fetch_limit(0),
  fetch_count(0),
  is_rnd_inited(0)
{
  fake_unit.init_query();
  fake_unit.thd= table->in_use;
}


/**
  Preserve the original metadata that would be sent to the client.

  @param thd Thread identifier.
  @param send_result_set_metadata List of fields that would be sent.
*/

int Materialized_cursor::fill_item_list(THD *thd,
                                        List<Item> &send_result_set_metadata)
{
  Query_arena backup_arena;
  int rc;
  List_iterator_fast<Item> it_org(send_result_set_metadata);
  List_iterator_fast<Item> it_dst(item_list);
  Item *item_org;
  Item *item_dst;

  thd->set_n_backup_active_arena(this, &backup_arena);

  if ((rc= table->fill_item_list(&item_list)))
    goto end;

  DBUG_ASSERT(send_result_set_metadata.elements == item_list.elements);

  /*
    Unless we preserve the original metadata, it will be lost,
    since new fields describe columns of the temporary table.
    Allocate a copy of the name for safety only. Currently
    items with original names are always kept in memory,
    but in case this changes a memory leak may be hard to notice.
  */
  while ((item_dst= it_dst++, item_org= it_org++))
  {
    Send_field send_field;
    Item_ident *ident= static_cast<Item_ident *>(item_dst);
    item_org->make_field(&send_field);

    ident->db_name=    thd->strdup(send_field.db_name);
    ident->table_name= thd->strdup(send_field.table_name);
  }
end:
  thd->restore_active_arena(this, &backup_arena);
  /* Check for thd->is_error() in case of OOM */
  return rc || thd->is_error();
}


int Materialized_cursor::open(JOIN *join __attribute__((unused)))
{
  THD *thd= fake_unit.thd;
  int rc;
  Query_arena backup_arena;
  thd->set_n_backup_active_arena(this, &backup_arena);
  /* Create a list of fields and start sequential scan */
  rc= result->prepare(item_list, &fake_unit);
  if (!rc && !(rc= table->file->ha_rnd_init_with_error(TRUE)))
    is_rnd_inited= 1;

  thd->restore_active_arena(this, &backup_arena);
  if (rc == 0)
  {
    /*
      Now send the result set metadata to the client. We need to
      do it here, as in Select_materialize::send_result_set_metadata the items
      for column types are not yet created (send_result_set_metadata requires
      a list of items). The new types may differ from the original
      ones sent at prepare if some of them were altered by MySQL
      HEAP tables mechanism -- used when create_tmp_field_from_item
      may alter the original column type.

      We can't simply supply SEND_EOF flag to send_result_set_metadata, because
      send_result_set_metadata doesn't flush the network buffer.
    */
    rc= result->send_result_set_metadata(item_list, Protocol::SEND_NUM_ROWS);
    thd->server_status|= SERVER_STATUS_CURSOR_EXISTS;
    result->send_eof();
    thd->server_status&= ~SERVER_STATUS_CURSOR_EXISTS;
  }
  return rc;
}


/**
  Fetch up to the given number of rows from a materialized cursor.

    Precondition: the cursor is open.

    If the cursor points after the last row, the fetch will automatically
    close the cursor and not send any data (except the 'EOF' packet
    with SERVER_STATUS_LAST_ROW_SENT). This is an extra round trip
    and probably should be improved to return
    SERVER_STATUS_LAST_ROW_SENT along with the last row.
*/

void Materialized_cursor::fetch(ulong num_rows)
{
  THD *thd= table->in_use;

  int res= 0;
  result->begin_dataset();
  for (fetch_limit+= num_rows; fetch_count < fetch_limit; fetch_count++)
  {
    if ((res= table->file->ha_rnd_next(table->record[0])))
      break;
    /* Send data only if the read was successful. */
    /*
      If network write failed (i.e. due to a closed socked),
      the error has already been set. Just return.
    */
    if (result->send_data(item_list))
      return;
  }

  switch (res) {
  case 0:
    thd->server_status|= SERVER_STATUS_CURSOR_EXISTS;
    result->send_eof();
    thd->server_status&= ~SERVER_STATUS_CURSOR_EXISTS;
    break;
  case HA_ERR_END_OF_FILE:
    thd->server_status|= SERVER_STATUS_LAST_ROW_SENT;
    result->send_eof();
    thd->server_status&= ~SERVER_STATUS_LAST_ROW_SENT;
    close();
    break;
  default:
    table->file->print_error(res, MYF(0));
    close();
    break;
  }
}


void Materialized_cursor::close()
{
  /* Free item_list items */
  free_items();
  if (is_rnd_inited)
    (void) table->file->ha_rnd_end();
  /*
    We need to grab table->mem_root to prevent free_tmp_table from freeing:
    the cursor object was allocated in this memory.
  */
  main_mem_root= table->mem_root;
  mem_root= &main_mem_root;
  clear_alloc_root(&table->mem_root);
  free_tmp_table(table->in_use, table);
  table= 0;
}


Materialized_cursor::~Materialized_cursor()
{
  if (is_open())
    close();
}


/***************************************************************************
 Select_materialize
****************************************************************************/

bool Select_materialize::send_result_set_metadata(List<Item> &list, uint flags)
{
  DBUG_ASSERT(table == 0);
  if (create_result_table(unit->thd, unit->get_unit_column_types(),
                          FALSE,
                          thd->variables.option_bits | TMP_TABLE_ALL_COLUMNS,
                          "", FALSE))
    return TRUE;

  materialized_cursor= new (&table->mem_root)
                       Materialized_cursor(result, table);

  if (! materialized_cursor)
  {
    free_tmp_table(table->in_use, table);
    table= 0;
    return TRUE;
  }
  if (materialized_cursor->fill_item_list(unit->thd, list))
  {
    delete materialized_cursor;
    table= 0;
    materialized_cursor= 0;
    return TRUE;
  }

  return FALSE;
}