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BUG#913030: better comments and function names.

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This commit is contained in:
Sergey Petrunya 2012-04-04 12:26:36 +04:00
parent d734a13d05
commit 656c284d81
1 changed files with 44 additions and 4 deletions
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48
sql/sql_select.cc
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@ -5635,6 +5635,15 @@ best_access_path(JOIN *join,
}
/*
Find JOIN_TAB's embedding (i.e, parent) subquery.
- For merged semi-joins, tables inside the semi-join nest have their
semi-join nest as parent. We intentionally ignore results of table
pullout action here.
- For non-merged semi-joins (JTBM tabs), the embedding subquery is the
JTBM join tab itself.
*/
static TABLE_LIST* get_emb_subq(JOIN_TAB *tab)
{
TABLE_LIST *tlist= tab->table->pos_in_table_list;
@ -5648,8 +5657,21 @@ static TABLE_LIST* get_emb_subq(JOIN_TAB *tab)
/*
Choose initial table order that "helps" semi-join optimizations.
The idea is that we should start with the order that is the same as the one
we would have had if we had semijoin=off:
- Top-level tables go first
- subquery tables are grouped together by the subquery they are in,
- subquery tables are attached where the subquery predicate would have been
attached if we had semi-join off.
This function relies on join_tab_cmp()/join_tab_cmp_straight() to produce
certain pre-liminary ordering, see compare_embedding_subqueries() for its
description.
*/
static void pre_sort_tables(JOIN *join)
static void choose_initial_table_order(JOIN *join)
{
TABLE_LIST *emb_subq;
JOIN_TAB **tab= join->best_ref + join->const_tables;
@ -5660,10 +5682,12 @@ static void pre_sort_tables(JOIN *join)
if ((emb_subq= get_emb_subq(*tab)))
break;
}
/* Copy the subquery JOIN_TABs to a separate array */
uint n_subquery_tabs= tabs_end - tab;
if (!n_subquery_tabs)
return;
/* Copy the subquery JOIN_TABs to a separate array */
JOIN_TAB *subquery_tabs[MAX_TABLES];
memcpy(subquery_tabs, tab, sizeof(JOIN_TAB*) * n_subquery_tabs);
@ -5787,7 +5811,7 @@ choose_plan(JOIN *join, table_map join_tables)
if (!join->emb_sjm_nest)
{
pre_sort_tables(join);
choose_initial_table_order(join);
}
join->cur_sj_inner_tables= 0;
@ -5828,6 +5852,18 @@ choose_plan(JOIN *join, table_map join_tables)
}
/*
Compare two join tabs based on the subqueries they are from.
- top-level join tabs go first
- then subqueries are ordered by their select_id (we're using this
criteria because we need a cross-platform, deterministic ordering)
@return
0 - equal
-1 - jt1 < jt2
1 - jt1 > jt2
*/
static int compare_embedding_subqueries(JOIN_TAB *jt1, JOIN_TAB *jt2)
{
/* Determine if the first table is originally from a subquery */
@ -5865,7 +5901,8 @@ static int compare_embedding_subqueries(JOIN_TAB *jt1, JOIN_TAB *jt2)
/*
Put top-level tables in front. Tables from within subqueries must follow,
grouped by their owner subquery. We don't care about the order that
subquery groups are in, because pre_sort_tables() will move the groups.
subquery groups are in, because choose_initial_table_order() will re-order
the groups.
*/
if (tbl1_select_no != tbl2_select_no)
return tbl1_select_no > tbl2_select_no ? 1 : -1;
@ -5889,6 +5926,9 @@ static int compare_embedding_subqueries(JOIN_TAB *jt1, JOIN_TAB *jt2)
a: dependent = 0x0 table->map = 0x1 found_records = 3 ptr = 0x907e6b0
b: dependent = 0x0 table->map = 0x2 found_records = 3 ptr = 0x907e838
c: dependent = 0x6 table->map = 0x10 found_records = 2 ptr = 0x907ecd0
As for subuqueries, this function must produce order that can be fed to
choose_initial_table_order().
@retval
1 if first is bigger