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/* -*- mode: c++; c-basic-offset: 2; indent-tabs-mode: nil; -*-
* vim:expandtab:shiftwidth=2:tabstop=2:smarttab:
*
* Copyright (C) 2008-2009 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_OPTIMIZER_QUICK_INDEX_MERGE_SELECT_H
#define DRIZZLED_OPTIMIZER_QUICK_INDEX_MERGE_SELECT_H
#include "drizzled/optimizer/range.h"
#include <vector>
namespace drizzled
{
namespace optimizer
{
/**
@class QuickIndexMergeSelect - index_merge access method quick select.
QuickIndexMergeSelect uses
* QuickRangeSelects to get rows
* Unique class to remove duplicate rows
INDEX MERGE OPTIMIZER
Current implementation doesn't detect all cases where index_merge could
be used, in particular:
* index_merge will never be used if range scan is possible (even if
range scan is more expensive)
* index_merge+'using index' is not supported (this the consequence of
the above restriction)
* If WHERE part contains complex nested AND and OR conditions, some ways
to retrieve rows using index_merge will not be considered. The choice
of read plan may depend on the order of conjuncts/disjuncts in WHERE
part of the query, see comments near imerge_list_or_list and
SEL_IMERGE::or_sel_tree_with_checks functions for details.
* There is no "index_merge_ref" method (but index_merge on non-first
table in join is possible with 'range checked for each record').
See comments around SEL_IMERGE class and test_quick_select for more
details.
ROW RETRIEVAL ALGORITHM
index_merge uses Unique class for duplicates removal. index_merge takes
advantage of Clustered Primary Key (CPK) if the table has one.
The index_merge algorithm consists of two phases:
Phase 1 (implemented in QuickIndexMergeSelect::prepare_unique):
prepare()
{
activate 'index only';
while(retrieve next row for non-CPK scan)
{
if (there is a CPK scan and row will be retrieved by it)
skip this row;
else
put its rowid into Unique;
}
deactivate 'index only';
}
Phase 2 (implemented as sequence of QuickIndexMergeSelect::get_next
calls):
fetch()
{
retrieve all rows from row pointers stored in Unique;
free Unique;
retrieve all rows for CPK scan;
}
*/
class QuickIndexMergeSelect : public QuickSelectInterface
{
public:
QuickIndexMergeSelect(Session *session, Table *table);
~QuickIndexMergeSelect();
int init();
int reset(void);
/**
* Get next row for index_merge.
* NOTES
* The rows are read from
* 1. rowids stored in Unique.
* 2. QuickRangeSelect with clustered primary key (if any).
* The sets of rows retrieved in 1) and 2) are guaranteed to be disjoint.
*/
int get_next();
bool reverse_sorted() const
{
return false;
}
bool unique_key_range() const
{
return false;
}
int get_type() const
{
return QS_TYPE_INDEX_MERGE;
}
void add_keys_and_lengths(String *key_names, String *used_lengths);
void add_info_string(String *str);
bool is_keys_used(const MyBitmap *fields);
bool push_quick_back(QuickRangeSelect *quick_sel_range);
/* range quick selects this index_merge read consists of */
std::vector<QuickRangeSelect *> quick_selects;
/* quick select that uses clustered primary key (NULL if none) */
QuickRangeSelect *pk_quick_select;
/* true if this select is currently doing a clustered PK scan */
bool doing_pk_scan;
memory::Root alloc;
Session *session;
/**
* Perform key scans for all used indexes (except CPK), get rowids and merge
* them into an ordered non-recurrent sequence of rowids.
*
* The merge/duplicate removal is performed using Unique class. We put all
* rowids into Unique, get the sorted sequence and destroy the Unique.
*
* If table has a clustered primary key that covers all rows (true for bdb
* and innodb currently) and one of the index_merge scans is a scan on PK,
* then rows that will be retrieved by PK scan are not put into Unique and
* primary key scan is not performed here, it is performed later separately.
*
* RETURN
* @retval 0 OK
* @retval other error
*/
int read_keys_and_merge();
/* used to get rows collected in Unique */
ReadRecord read_record;
};
} /* namespace optimizer */
} /* namespace drizzled */
#endif /* DRIZZLED_OPTIMIZER_QUICK_INDEX_MERGE_SELECT_H */
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