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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
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8
dbcon/mysql/ha_mcs_impl.cpp
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@ -4679,8 +4679,8 @@ int ha_mcs_impl_pushdown_init(mcs_handler_info* handler_info, TABLE* table)
sm::cpsm_conhdl_t* hndl;
SCSEP csep;
// Declare handlers ptrs in this scope for future use.
select_handler* sh = nullptr;
derived_handler* dh = nullptr;
ha_columnstore_select_handler* sh = nullptr;
ha_columnstore_derived_handler* dh = nullptr;
// update traceFlags according to the autoswitch state.
ci->traceFlags = (ci->traceFlags | CalpontSelectExecutionPlan::TRACE_TUPLE_OFF)^
@ -4774,12 +4774,12 @@ int ha_mcs_impl_pushdown_init(mcs_handler_info* handler_info, TABLE* table)
int status = 42;
if (handler_info->hndl_type == mcs_handler_types_t::SELECT)
{
sh = reinterpret_cast<select_handler*>(handler_info->hndl_ptr);
sh = reinterpret_cast<ha_columnstore_select_handler*>(handler_info->hndl_ptr);
status = cs_get_select_plan(sh, thd, csep, gwi);
}
else if (handler_info->hndl_type == DERIVED)
{
dh = reinterpret_cast<derived_handler*>(handler_info->hndl_ptr);
dh = reinterpret_cast<ha_columnstore_derived_handler*>(handler_info->hndl_ptr);
status = cs_get_derived_plan(dh, thd, csep, gwi);
}