~drizzle-trunk/drizzle/development

/* -*- mode: c++; c-basic-offset: 2; indent-tabs-mode: nil; -*-

 *  vim:expandtab:shiftwidth=2:tabstop=2:smarttab:

 *

 *  Copyright (C) 2009 Sun Microsystems

 *

 *  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., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

 */

#ifndef DRIZZLED_RECORDS_H

#define DRIZZLED_RECORDS_H

namespace drizzled

{

/**

  Initialize READ_RECORD structure to perform full index scan (in forward

  direction) using read_record.read_record() interface.

    This function has been added at late stage and is used only by

    UPDATE/DELETE. Other statements perform index scans using

    join_read_first/next functions.

  @param info         READ_RECORD structure to initialize.

  @param session          Thread handle

  @param table        Table to be accessed

  @param print_error  If true, call table->print_error() if an error

                      occurs (except for end-of-records error)

  @param idx          index to scan

*/

void init_read_record_idx(READ_RECORD *info, 

                          Session *session, 

                          Table *table,

                          bool print_error, 

                          uint32_t idx);

/*

  init_read_record is used to scan by using a number of different methods.

  Which method to use is set-up in this call so that later calls to

  the info->read_record will call the appropriate method using a function

  pointer.

  There are five methods that relate completely to the sort function

  filesort. The result of a filesort is retrieved using read_record

  calls. The other two methods are used for normal table access.

  The filesort will produce references to the records sorted, these

  references can be stored in memory or in a temporary cursor.

  The temporary cursor is normally used when the references doesn't fit into

  a properly sized memory buffer. For most small queries the references

  are stored in the memory buffer.

  The temporary cursor is also used when performing an update where a key is

  modified.

  Methods used when ref's are in memory (using rr_from_pointers):

    rr_unpack_from_buffer:

    ----------------------

      This method is used when table->sort.addon_field is allocated.

      This is allocated for most SELECT queries not involving any BLOB's.

      In this case the records are fetched from a memory buffer.

    rr_from_pointers:

    -----------------

      Used when the above is not true, UPDATE, DELETE and so forth and

      SELECT's involving BLOB's. It is also used when the addon_field

      buffer is not allocated due to that its size was bigger than the

      session variable max_length_for_sort_data.

      In this case the record data is fetched from the handler using the

      saved reference using the rnd_pos handler call.

  Methods used when ref's are in a temporary cursor (using rr_from_tempfile)

    rr_unpack_from_tempfile:

    ------------------------

      Same as rr_unpack_from_buffer except that references are fetched from

      temporary cursor. Should obviously not really happen other than in

      strange configurations.

    rr_from_tempfile:

    -----------------

      Same as rr_from_pointers except that references are fetched from

      temporary cursor instead of from

    rr_from_cache:

    --------------

      This is a special variant of rr_from_tempfile that can be used for

      handlers that is not using the HA_FAST_KEY_READ table flag. Instead

      of reading the references one by one from the temporary cursor it reads

      a set of them, sorts them and reads all of them into a buffer which

      is then used for a number of subsequent calls to rr_from_cache.

      It is only used for SELECT queries and a number of other conditions

      on table size.

  All other accesses use either index access methods (rr_quick) or a full

  table scan (rr_sequential).

  rr_quick:

  ---------

    rr_quick uses one of the QUICK_SELECT classes in optimizer/range.cc to

    perform an index scan. There are loads of functionality hidden

    in these quick classes. It handles all index scans of various kinds.

  rr_sequential:

  --------------

    This is the most basic access method of a table using rnd_init,

    rnd_next and rnd_end. No indexes are used.

*/

void init_read_record(READ_RECORD *info, 

                      Session *session, 

                      Table *reg_form,

                      optimizer::SqlSelect *select,

                      int use_record_cache, 

                      bool print_errors);

void end_read_record(READ_RECORD *info);

} /* namespace drizzled */

#endif /* DRIZZLED_RECORDS_H */