This feature allows a query execution to fallback to the server,
in case query execution using the select_handler (SH) fails. In case
of fallback, a warning message containing the original reason for
query failure using SH is generated.
To accomplish this task, SH execution is moved to an earlier step when
we create the SH in create_columnstore_select_handler(), instead of the
previous call to SH execution in ha_columnstore_select_handler::init_scan().
This requires some pre-requisite steps that occur in the server in
JOIN::optimize() and JOIN::exec() to be performed before starting SH execution.
In addition, missing test cases from MCOL-424 are also added to the MTR suite,
and the corresponding fix using disable_indices_for_CEJ() is reverted back
since the original fix now appears to be redundant.
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 patch enables select handler for executing prepared
statements. Most importantly, we are now activating a
persistent arena which will allocate any new items in a
permanent MEMROOT for prepared statements and stored procedures.
Refer to JOIN::optimize_inner() for details.
In processWhere(), we now use SELECT_LEX::prep_where in case
we are executing a prepared statement, as this is where the saved
WHERE clause is stored for prepared statement processing.
In addition, we also disable derived handler for prepared
statements.
internally(thus can remove equi-JOIN predicates) with a recursive f()
to inject equi-JOIN conditions for IN + correlated subquery Item.
This change both solves MCOL-3747 issue and remove issues I first
faced in union.sql test.
This commit also fixes a clean up for conditions pushed for table API
execution path and replaces NULL with nullptr in ha_mcs_impl.cpp.
Disabled 4th if block in buildOuterJoin to handle non-optimized MDB query
structures.
Broke getSelectPlan into pieces: processFrom, processWhere.
MCOL-3593 UNION processing depends on two flags isUnion that comes as
arg of getSelectPlan and unionSel that is a local variable in
getSelectPlan. Modularization of getSelectPlan broke the mechanizm.
This patch is supposed to partially fix it.
MCOL-3593 Removed unused if condition from buildOuterJoin that allows
unsupported construct subquery in ON expression.
Fixed an improper if condition that ignors tableMap entries w/o condition
in external_lock thus external_lock doesn't clean up when the query
finishes.
Fixed wrong logging for queries processed in tableMode. Now rnd_init
properly sends queryText down to ExeMgr to be logged.
MCOL-3593 Unused attribute FromSubQuery::fFromSub was removed.
getSelectPlan has been modularized into: setExecutionParams,
processFrom, processWhere. SELECT, HAVING, GROUP BY, ORDER BY
still lives in getSelectPlan.
Copied optimization function simplify_joins_ into our pushdown
code to provide the plugin code with some rewrites from MDB it
expects.
The columnstore_processing_handlers_fallback session variable
has been removed thus CS can't fallback from SH to partial
execution paths, e.g. DH, GBH or plugin API.
MCOL-3602 Moved MDB optimizer rewrites into a separate file.
Add SELECT_LEX::optimize_unflattened_subqueries() call to fix IN
into EXISTS rewrite for semi-JOINs with subqueries.
disable_indices_for_CEJ() add index related hints to disable
index access methods in Cross Engine Joins.
create_SH() now flattens JOIN that has both physical tables and
views. This fixes most of views related tests in the regression.
