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MDEV-36092 New-style hint: [NO_]SPLIT_MATERIALIZED

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Support for optimizer hints NO_SPLIT_MATERIALIZED and
SPLIT_MATERIALIZED.  These hints allow fine-grained control
of the "lateral derived" optimization within a query.

Introduces new overload of hint_table_state function which
tells both a hint's value as well as whether it is present.
This is useful to disambiguate cases that the other version
of hint_table_state cannot, such as when a hint is forcing
a behavior in the optimizer that it would not normally do
and the corresponding optimizer switch is enabled.
This commit is contained in:
Dave Gosselin
2025-04-24 15:03:05 -04:00
committed by Dave Gosselin
parent 07d71fdcf8
commit 62a1f0d990
8 changed files with 1467 additions and 26 deletions
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72
sql/opt_split.cc
View File

@@ -228,6 +228,7 @@
#include "mariadb.h"
#include "sql_select.h"
#include "opt_hints.h"
#include "opt_trace.h"
#include "optimizer_defaults.h"
@@ -273,7 +274,7 @@ class SplM_opt_info : public Sql_alloc
public:
/* The join for the select specifying T */
JOIN *join;
/* The map of tables from 'join' whose columns can be used for partitioning */
/* The map of tables from 'join' whose columns can be used for partitioning */
table_map tables_usable_for_splitting;
/* Info about the fields of the joined tables usable for splitting */
SplM_field_info *spl_fields;
@@ -292,6 +293,8 @@ public:
/* Cardinality of T when nothing is pushed */
double unsplit_card;
double last_refills;
/* True when SPLIT_MATERIALIZED hint present and forces this split. */
bool hint_forced_split{false};
SplM_plan_info *find_plan(TABLE *table, uint key, uint parts);
};
@@ -299,8 +302,8 @@ public:
void TABLE::set_spl_opt_info(SplM_opt_info *spl_info)
{
if (spl_info)
spl_info->join->spl_opt_info= spl_info;
DBUG_ASSERT(spl_info);
spl_info->join->spl_opt_info= spl_info;
spl_opt_info= spl_info;
}
@@ -320,6 +323,40 @@ double TABLE::get_materialization_cost()
}
/**
Returns true if split materialization is permitted for the
derived table passed in argument 'derived'.
@param thd The connection state for the current thread.
@param derived The candidate derived table for split materialization.
@param hint [OUT] One of the values from the hint_state enumeration
found in opt_hints.h
@return true if split materialization allowed, either by hint
or by optimizer option. The hint takes precedence.
*/
static bool is_split_materialized_allowed(THD *thd,
const TABLE_LIST *derived,
hint_state *hint)
{
if (!derived)
{
*hint= hint_state::DISABLED; // there is no derived table to hint on
return false;
}
*hint= hint_table_state(thd,
derived,
SPLIT_MATERIALIZED_HINT_ENUM);
const bool opt_flag= optimizer_flag(thd, OPTIMIZER_SWITCH_SPLIT_MATERIALIZED);
const bool allow_split= (*hint == hint_state::ENABLED ||
(*hint == hint_state::NOT_PRESENT && opt_flag));
return allow_split;
}
/* This structure is auxiliary and used only in the function that follows it */
struct SplM_field_ext_info: public SplM_field_info
{
@@ -330,7 +367,8 @@ struct SplM_field_ext_info: public SplM_field_info
/**
@brief
Check whether this join is one for potentially splittable materialized table
Check whether this join is one for potentially splittable materialized
table
@details
The function checks whether this join is for select that specifies
@@ -339,7 +377,8 @@ struct SplM_field_ext_info: public SplM_field_info
of the TABLE structure for T.
The function returns a positive answer if the following holds:
1. the optimizer switch 'split_materialized' is set 'on'
1. The is_split_materialized_allowed() function indicates that split
materialization is permitted for the derived table.
2. the select owning this join specifies a materialized derived/view/cte T
3. this is the only select in the specification of T
4. condition pushdown is not prohibited into T
@@ -355,7 +394,7 @@ struct SplM_field_ext_info: public SplM_field_info
9. There are defined some keys usable for ref access of fields from C
with available statistics.
10. The select doesn't use WITH ROLLUP (This limitation can probably be
lifted)
lifted)
@retval
true if the answer is positive
@@ -367,8 +406,10 @@ bool JOIN::check_for_splittable_materialized()
ORDER *partition_list= 0;
st_select_lex_unit *unit= select_lex->master_unit();
TABLE_LIST *derived= unit->derived;
if (!(optimizer_flag(thd, OPTIMIZER_SWITCH_SPLIT_MATERIALIZED)) || // !(1)
!(derived && derived->is_materialized_derived()) || // !(2)
hint_state hint;
if (!is_split_materialized_allowed(thd, derived, &hint) || // !(1)
!derived->is_materialized_derived() || // !(2)
(unit->first_select()->next_select()) || // !(3)
(derived->prohibit_cond_pushdown) || // !(4)
(derived->is_recursive_with_table()) || // !(5)
@@ -519,6 +560,7 @@ bool JOIN::check_for_splittable_materialized()
spl_opt_info->tables_usable_for_splitting= 0;
spl_opt_info->spl_field_cnt= spl_field_cnt;
spl_opt_info->spl_fields= spl_field;
spl_opt_info->hint_forced_split= (hint == hint_state::ENABLED);
{
Json_writer_array trace_range(thd, "split_candidates");
@@ -1130,8 +1172,8 @@ SplM_plan_info * JOIN_TAB::choose_best_splitting(uint idx,
spl_plan->cost= (join->best_positions[join->table_count-1].read_time +
oper_cost);
chosen= (refills * spl_plan->cost + COST_EPS <
spl_opt_info->unsplit_cost);
chosen= ((refills * spl_plan->cost + COST_EPS <
spl_opt_info->unsplit_cost) || spl_opt_info->hint_forced_split);
if (unlikely(thd->trace_started()))
{
@@ -1149,6 +1191,9 @@ SplM_plan_info * JOIN_TAB::choose_best_splitting(uint idx,
add("refills", refills).
add("total_splitting_cost", refills * spl_plan->cost).
add("chosen", chosen);
if (spl_opt_info->hint_forced_split)
find_trace.add("forced_by_hint", true);
}
memcpy((char *) spl_plan->best_positions,
(char *) join->best_positions,
@@ -1160,8 +1205,11 @@ SplM_plan_info * JOIN_TAB::choose_best_splitting(uint idx,
else
{
trace_obj.add("cached_plan_found", 1);
chosen= (refills * spl_plan->cost + COST_EPS <
spl_opt_info->unsplit_cost);
if (spl_opt_info->hint_forced_split)
trace_obj.add("forced_by_hint", true);
chosen= ((refills * spl_plan->cost + COST_EPS <
spl_opt_info->unsplit_cost) || spl_opt_info->hint_forced_split);
already_printed= 0;
}
}