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MCOL-4665 Move outer join to inner join conversion into the engine.

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This is a subtask of MCOL-4525 Implement select_handler=AUTO.

Server performs outer join to inner join conversion using simplify_joins()
in sql/sql_select.cc, by updating the TABLE_LIST::outer_join variable.
In order to perform this conversion, permanent changes are made in some
cases to the SELECT_LEX::JOIN::conds and/or TABLE_LIST::on_expr.
This is undesirable for MCOL-4525 which will attemp to fallback and execute
the query inside the server, in case the query execution fails in ColumnStore
using the select_handler.

For a query such as:
  SELECT * FROM t1 LEFT JOIN t2 ON expr1 LEFT JOIN t3 ON expr2
In some cases, server can update the original SELECT_LEX::JOIN::conds
and/or TABLE_LIST::on_expr and create new Item_cond_and objects
(e.g. with 2 Item's expr1 and expr2 in Item_cond_and::list).
Instead of making changes to the original query structs, we use
gp_walk_info::tableOnExprList and gp_walk_info::condList. 2 Item's,
expr1 and expr2, in the condList, mean Item_cond_and(expr1, expr2), and
hence avoid permanent transformations to the SELECT_LEX.

We also define a new member variable
ha_columnstore_select_handler::tableOuterJoinMap
which saves the original TABLE_LIST::outer_join values before they are
updated. This member variable will be used later on to restore to the original
state of TABLE_LIST::outer_join in case of a query fallback to server execution.

The original simplify_joins() implementation in the server also performs a
flattening of the JOIN nest, however we don't perform this operation in
convertOuterJoinToInnerJoin() since it is not required for ColumnStore.
This commit is contained in:
Gagan Goel
2021-05-17 09:53:23 +00:00
parent 4d835d78d3
commit e0d2a21cb9
9 changed files with 600 additions and 376 deletions
Download Patch File Download Diff File Expand all files Collapse all files

252
dbcon/mysql/ha_mcs_opt_rewrites.cpp
View File

@ -19,234 +19,6 @@
#include "ha_mcs_opt_rewrites.h"
// Search simplify_joins() function in the server's code for detail
COND *
simplify_joins_mcs(JOIN *join, List<TABLE_LIST> *join_list, COND *conds, bool top,
bool in_sj)
{
TABLE_LIST *table;
NESTED_JOIN *nested_join;
TABLE_LIST *prev_table= 0;
List_iterator<TABLE_LIST> li(*join_list);
bool straight_join= MY_TEST(join->select_options & SELECT_STRAIGHT_JOIN);
DBUG_ENTER("simplify_joins_mcs");
/*
Try to simplify join operations from join_list.
The most outer join operation is checked for conversion first.
*/
while ((table= li++))
{
table_map used_tables;
table_map not_null_tables= (table_map) 0;
if ((nested_join= table->nested_join))
{
/*
If the element of join_list is a nested join apply
the procedure to its nested join list first.
*/
if (table->on_expr)
{
Item *expr= table->on_expr;
/*
If an on expression E is attached to the table,
check all null rejected predicates in this expression.
If such a predicate over an attribute belonging to
an inner table of an embedded outer join is found,
the outer join is converted to an inner join and
the corresponding on expression is added to E.
*/
expr= simplify_joins_mcs(join, &nested_join->join_list,
expr, FALSE, in_sj || table->sj_on_expr);
if (!table->prep_on_expr || expr != table->on_expr)
{
DBUG_ASSERT(expr);
table->on_expr= expr;
table->prep_on_expr= expr->copy_andor_structure(join->thd);
}
}
nested_join->used_tables= (table_map) 0;
nested_join->not_null_tables=(table_map) 0;
conds= simplify_joins_mcs(join, &nested_join->join_list, conds, top,
in_sj || table->sj_on_expr);
used_tables= nested_join->used_tables;
not_null_tables= nested_join->not_null_tables;
/* The following two might become unequal after table elimination: */
nested_join->n_tables= nested_join->join_list.elements;
}
else
{
if (!table->prep_on_expr)
table->prep_on_expr= table->on_expr;
used_tables= table->get_map();
if (conds)
not_null_tables= conds->not_null_tables();
}
if (table->embedding)
{
table->embedding->nested_join->used_tables|= used_tables;
table->embedding->nested_join->not_null_tables|= not_null_tables;
}
if (!(table->outer_join & (JOIN_TYPE_LEFT | JOIN_TYPE_RIGHT)) ||
(used_tables & not_null_tables))
{
/*
For some of the inner tables there are conjunctive predicates
that reject nulls => the outer join can be replaced by an inner join.
*/
if (table->outer_join && !table->embedding && table->table)
table->table->maybe_null= FALSE;
table->outer_join= 0;
if (!(straight_join || table->straight))
{
table->dep_tables= 0;
TABLE_LIST *embedding= table->embedding;
while (embedding)
{
if (embedding->nested_join->join_list.head()->outer_join)
{
if (!embedding->sj_subq_pred)
table->dep_tables= embedding->dep_tables;
break;
}
embedding= embedding->embedding;
}
}
if (table->on_expr)
{
/* Add ON expression to the WHERE or upper-level ON condition. */
if (conds)
{
conds= and_conds(join->thd, conds, table->on_expr);
conds->top_level_item();
/* conds is always a new item as both cond and on_expr existed */
DBUG_ASSERT(!conds->fixed());
conds->fix_fields(join->thd, &conds);
}
else
conds= table->on_expr;
table->prep_on_expr= table->on_expr= 0;
}
}
/*
Only inner tables of non-convertible outer joins
remain with on_expr.
*/
if (table->on_expr)
{
table_map table_on_expr_used_tables= table->on_expr->used_tables();
table->dep_tables|= table_on_expr_used_tables;
if (table->embedding)
{
table->dep_tables&= ~table->embedding->nested_join->used_tables;
/*
Embedding table depends on tables used
in embedded on expressions.
*/
table->embedding->on_expr_dep_tables|= table_on_expr_used_tables;
}
else
table->dep_tables&= ~table->get_map();
}
if (prev_table)
{
/* The order of tables is reverse: prev_table follows table */
if (prev_table->straight || straight_join)
prev_table->dep_tables|= used_tables;
if (prev_table->on_expr)
{
prev_table->dep_tables|= table->on_expr_dep_tables;
table_map prev_used_tables= prev_table->nested_join ?
prev_table->nested_join->used_tables :
prev_table->get_map();
/*
If on expression contains only references to inner tables
we still make the inner tables dependent on the outer tables.
It would be enough to set dependency only on one outer table
for them. Yet this is really a rare case.
Note:
RAND_TABLE_BIT mask should not be counted as it
prevents update of inner table dependences.
For example it might happen if RAND() function
is used in JOIN ON clause.
*/
if (!((prev_table->on_expr->used_tables() &
~(OUTER_REF_TABLE_BIT | RAND_TABLE_BIT)) &
~prev_used_tables))
prev_table->dep_tables|= used_tables;
}
}
prev_table= table;
}
/*
Flatten nested joins that can be flattened.
no ON expression and not a semi-join => can be flattened.
*/
li.rewind();
while ((table= li++))
{
nested_join= table->nested_join;
if (table->sj_on_expr && !in_sj)
{
/*
If this is a semi-join that is not contained within another semi-join
leave it intact (otherwise it is flattened)
*/
/*
Make sure that any semi-join appear in
the join->select_lex->sj_nests list only once
*/
List_iterator_fast<TABLE_LIST> sj_it(join->select_lex->sj_nests);
TABLE_LIST *sj_nest;
while ((sj_nest= sj_it++))
{
if (table == sj_nest)
break;
}
if (sj_nest)
continue;
join->select_lex->sj_nests.push_back(table, join->thd->mem_root);
/*
Also, walk through semi-join children and mark those that are now
top-level
*/
TABLE_LIST *tbl;
List_iterator<TABLE_LIST> it(nested_join->join_list);
while ((tbl= it++))
{
if (!tbl->on_expr && tbl->table)
tbl->table->maybe_null= FALSE;
}
}
else if (nested_join && !table->on_expr)
{
TABLE_LIST *tbl;
List_iterator<TABLE_LIST> it(nested_join->join_list);
List<TABLE_LIST> repl_list;
while ((tbl= it++))
{
tbl->embedding= table->embedding;
if (!tbl->embedding && !tbl->on_expr && tbl->table)
tbl->table->maybe_null= FALSE;
tbl->join_list= table->join_list;
repl_list.push_back(tbl, join->thd->mem_root);
tbl->dep_tables|= table->dep_tables;
}
li.replace(repl_list);
}
}
DBUG_RETURN(conds);
}
/*@brief in_subselect_rewrite_walk - Rewrites Item_in_subselect*/
/************************************************************
* DESCRIPTION:
@ -367,27 +139,3 @@ bool in_subselect_rewrite(SELECT_LEX *select_lex)
return result;
}
uint build_bitmap_for_nested_joins_mcs(List<TABLE_LIST> *join_list,
uint first_unused)
{
List_iterator<TABLE_LIST> li(*join_list);
TABLE_LIST *table;
DBUG_ENTER("build_bitmap_for_nested_joins_mcs");
while ((table= li++))
{
NESTED_JOIN *nested_join;
if ((nested_join= table->nested_join))
{
if (nested_join->n_tables != 1)
{
/* Don't assign bits to sj-nests */
if (table->on_expr)
nested_join->nj_map= (nested_join_map) 1 << first_unused++;
first_unused= build_bitmap_for_nested_joins_mcs(&nested_join->join_list,
first_unused);
}
}
}
DBUG_RETURN(first_unused);
}