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Precise read time estimates for index_merge/Unique

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unknown
2003-12-18 06:08:00 +03:00
parent 211bc24063
commit 7dbdedcb72
13 changed files with 606 additions and 212 deletions
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96
sql/opt_range.h
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@ -118,11 +118,13 @@ public:
protected:
friend void print_quick_sel_range(QUICK_RANGE_SELECT *quick,
const key_map* needed_reg);
friend QUICK_RANGE_SELECT *get_quick_select_for_ref(THD *thd, TABLE *table,
struct st_table_ref *ref);
friend
QUICK_RANGE_SELECT *get_quick_select_for_ref(THD *thd, TABLE *table,
struct st_table_ref *ref);
friend bool get_quick_keys(struct st_qsel_param *param,
QUICK_RANGE_SELECT *quick,KEY_PART *key,
SEL_ARG *key_tree,char *min_key,uint min_key_flag,
SEL_ARG *key_tree,
char *min_key, uint min_key_flag,
char *max_key, uint max_key_flag);
friend QUICK_RANGE_SELECT *get_quick_select(struct st_qsel_param*,uint idx,
SEL_ARG *key_tree,
@ -160,58 +162,62 @@ public:
/*
QUICK_INDEX_MERGE_SELECT - index_merge acces method quick select.
QUICK_INDEX_MERGE_SELECT - index_merge access method quick select.
QUICK_INDEX_MERGE_SELECT uses
* QUICK_RANGE_SELECTs to get rows
* Unique class to remove duplicate rows
QUICK_INDEX_MERGE_SELECT uses
* QUICK_RANGE_SELECTs 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 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)
* 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 SEL_IMERGE::or_sel_tree_with_checks and
imerge_list_or_list function for details.
* 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').
* 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.
See comments around SEL_IMERGE class and test_quick_select for more
details.
ROW RETRIEVAL ALGORITHM
ROW RETRIEVAL ALGORITHM
index_merge uses Unique class for duplicates removal. Index merge takes
advantage of clustered covering primary key (CCPK) if the table has one.
The algorithm is as follows:
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:
prepare() //implemented in QUICK_INDEX_MERGE_SELECT::prepare_unique
{
activate 'index only';
while(retrieve next row for non-CCPK scan)
Phase 1 (implemented in QUICK_INDEX_MERGE_SELECT::prepare_unique):
prepare()
{
if (there is a CCPK scan and row will be retrieved by it)
skip this row;
else
put rowid into Unique;
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';
}
deactivate 'index only';
}
fetch() //implemented as sequence of QUICK_INDEX_MERGE_SELECT::get_next calls
{
retrieve all rows from row pointers stored in Unique;
free Unique;
retrieve all rows for CCPK scan;
}
Phase 2 (implemented as sequence of QUICK_INDEX_MERGE_SELECT::get_next
calls):
fetch()
{
retrieve all rows from row pointers stored in Unique;
free Unique;
retrieve all rows for CPK scan;
}
*/
class QUICK_INDEX_MERGE_SELECT : public QUICK_SELECT_I
@ -239,10 +245,10 @@ public:
/* last element in quick_selects list */
QUICK_RANGE_SELECT* last_quick_select;
/* quick select that uses Covering Clustered Primary Key (NULL if none) */
/* quick select that uses clustered primary key (NULL if none) */
QUICK_RANGE_SELECT* pk_quick_select;
/* true if this select is currently doing a CCPK scan */
/* true if this select is currently doing a clustered PK scan */
bool doing_pk_scan;
Unique *unique;