MDEV-30812: Improve output cardinality estimates for hash join

Introduce @@optimizer_switch flag: hash_join_cardinality

When it is on, use EITS statistics to produce tighter bounds for
hash join output cardinality.

Amended by Monty.

Reviewed by: Monty <monty@mariadb.org>

mysql-test/main/join_cache_cardinality.result

+create table t1 (a int, b int, c int);
+insert into t1 select seq,seq/2, seq/4 from seq_1_to_100;
+create table t2 (a int, b int, c int);
+insert into t2 select seq, seq/2, seq/4 from seq_1_to_200;
+analyze table t1,t2 persistent for all;
+Table	Op	Msg_type	Msg_text
+test.t1	analyze	status	Engine-independent statistics collected
+test.t1	analyze	status	OK
+test.t2	analyze	status	Engine-independent statistics collected
+test.t2	analyze	status	OK
+set optimizer_trace=1;
+set join_cache_level=6;
+set optimizer_switch='hash_join_cardinality=on';
+explain select *
+from t1, t2
+where t1.a=t2.a and t1.a=t2.b and t1.c=t2.c;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	100	Using where
+1	SIMPLE	t2	hash_ALL	NULL	#hash#$hj	15	test.t1.a,test.t1.a,test.t1.c	200	Using where; Using join buffer (flat, BNLH join)
+set @json= (select trace from information_schema.optimizer_trace);
+select json_detailed(json_extract(@json, '$**.hash_join_cardinality')) as JS;
+JS
+[
+    {
+        "hash_join_columns": 
+        [
+            {
+                "field": "a",
+                "avg_frequency": 1
+            },
+            {
+                "field": "b",
+                "avg_frequency": 2
+            },
+            {
+                "field": "c",
+                "avg_frequency": 3.9216
+            }
+        ],
+        "rows": 1
+    }
+]
+select json_detailed(json_extract(@json, '$**.rest_of_plan[*].rows_for_plan'))
+as ROWS_FOR_PLAN;
+ROWS_FOR_PLAN
+[100]
+explain select *
+from t1, t2 where t1.c=t2.c;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	100	Using where
+1	SIMPLE	t2	hash_ALL	NULL	#hash#$hj	5	test.t1.c	200	Using where; Using join buffer (flat, BNLH join)
+set @json= (select trace from information_schema.optimizer_trace);
+select json_detailed(json_extract(@json, '$**.hash_join_cardinality')) as JS;
+JS
+[
+    {
+        "hash_join_columns": 
+        [
+            {
+                "field": "c",
+                "avg_frequency": 3.9216
+            }
+        ],
+        "rows": 3.9216
+    }
+]
+select json_detailed(json_extract(@json, '$**.rest_of_plan[*].rows_for_plan'))
+as ROWS_FOR_PLAN;
+ROWS_FOR_PLAN
+[392.16]
+explain select *
+from t1 straight_join t2 where t1.c=t2.c and t2.a<30;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	100	Using where
+1	SIMPLE	t2	hash_ALL	NULL	#hash#$hj	5	test.t1.c	200	Using where; Using join buffer (flat, BNLH join)
+set @json= (select trace from information_schema.optimizer_trace);
+# Note that rows is the same:
+select json_detailed(json_extract(@json, '$**.hash_join_cardinality')) as JS;
+JS
+[
+    {
+        "hash_join_columns": 
+        [
+            {
+                "field": "c",
+                "avg_frequency": 3.9216
+            }
+        ],
+        "rows": 3.9216
+    }
+]
+# Despite available selectivity:
+select json_detailed(json_extract(@json, '$**.selectivity_for_columns')) as JS;
+JS
+[
+    [
+        {
+            "column_name": "a",
+            "ranges": 
+            ["NULL < a < 30"],
+            "selectivity_from_histogram": 0.1484375
+        }
+    ]
+]
+drop table t1,t2;

mysql-test/main/join_cache_cardinality.test

+--source include/have_sequence.inc
+
+# Embedded doesn't have optimizer trace:
+--source include/not_embedded.inc
+
+create table t1 (a int, b int, c int);
+insert into t1 select seq,seq/2, seq/4 from seq_1_to_100;
+
+create table t2 (a int, b int, c int);
+insert into t2 select seq, seq/2, seq/4 from seq_1_to_200;
+
+analyze table t1,t2 persistent for all;
+
+set optimizer_trace=1;
+set join_cache_level=6;
+set optimizer_switch='hash_join_cardinality=on';
+explain select *
+from t1, t2
+where t1.a=t2.a and t1.a=t2.b and t1.c=t2.c;
+
+set @json= (select trace from information_schema.optimizer_trace);
+select json_detailed(json_extract(@json, '$**.hash_join_cardinality')) as JS;
+select json_detailed(json_extract(@json, '$**.rest_of_plan[*].rows_for_plan'))
+as ROWS_FOR_PLAN;
+
+explain select *
+from t1, t2 where t1.c=t2.c;
+set @json= (select trace from information_schema.optimizer_trace);
+select json_detailed(json_extract(@json, '$**.hash_join_cardinality')) as JS;
+select json_detailed(json_extract(@json, '$**.rest_of_plan[*].rows_for_plan'))
+as ROWS_FOR_PLAN;
+
+explain select *
+from t1 straight_join t2 where t1.c=t2.c and t2.a<30;
+set @json= (select trace from information_schema.optimizer_trace);
+--echo # Note that rows is the same:
+select json_detailed(json_extract(@json, '$**.hash_join_cardinality')) as JS;
+
+--echo # Despite available selectivity:
+select json_detailed(json_extract(@json, '$**.selectivity_for_columns')) as JS;
+drop table t1,t2;

mysql-test/main/mysqld--help.result

@@ -734,7 +734,8 @@ The following specify which files/extra groups are read (specified before remain
  extended_keys, exists_to_in, orderby_uses_equalities, 
  condition_pushdown_for_derived, split_materialized, 
  condition_pushdown_for_subquery, rowid_filter, 
- condition_pushdown_from_having, not_null_range_scan
+ condition_pushdown_from_having, not_null_range_scan, 
+ hash_join_cardinality
  --optimizer-trace=name 
  Controls tracing of the Optimizer:
  optimizer_trace=option=val[,option=val...], where option

mysql-test/main/mysqltest_tracking_info.result

@@ -38,7 +38,7 @@ SET @@session.session_track_system_variables='optimizer_switch';
 set optimizer_switch='index_merge=off,index_merge_union=off,index_merge_sort_union=off,index_merge_intersection=off,index_merge_sort_intersection=on,engine_condition_pushdown=on,index_condition_pushdown=off,derived_merge=off,derived_with_keys=off,firstmatch=off,loosescan=off,materialization=on,in_to_exists=off,semijoin=off,partial_match_rowid_merge=off,partial_match_table_scan=off,subquery_cache=off,mrr=on,mrr_cost_based=on,mrr_sort_keys=on,outer_join_with_cache=off,semijoin_with_cache=off,join_cache_incremental=off,join_cache_hashed=off,join_cache_bka=off,optimize_join_buffer_size=on,table_elimination=off,extended_keys=off,exists_to_in=off,orderby_uses_equalities=off,condition_pushdown_for_derived=off';
 -- Tracker : SESSION_TRACK_SYSTEM_VARIABLES
 -- optimizer_switch
--- index_merge=off,index_merge_union=off,index_merge_sort_union=off,index_merge_intersection=off,index_merge_sort_intersection=on,engine_condition_pushdown=on,index_condition_pushdown=off,derived_merge=off,derived_with_keys=off,firstmatch=off,loosescan=off,materialization=on,in_to_exists=off,semijoin=off,partial_match_rowid_merge=off,partial_match_table_scan=off,subquery_cache=off,mrr=on,mrr_cost_based=on,mrr_sort_keys=on,outer_join_with_cache=off,semijoin_with_cache=off,join_cache_incremental=off,join_cache_hashed=off,join_cache_bka=off,optimize_join_buffer_size=on,table_elimination=off,extended_keys=off,exists_to_in=off,orderby_uses_equalities=off,condition_pushdown_for_derived=off,split_materialized=on,condition_pushdown_for_subquery=on,rowid_filter=on,condition_pushdown_from_having=on,not_null_range_scan=off
+-- index_merge=off,index_merge_union=off,index_merge_sort_union=off,index_merge_intersection=off,index_merge_sort_intersection=on,engine_condition_pushdown=on,index_condition_pushdown=off,derived_merge=off,derived_with_keys=off,firstmatch=off,loosescan=off,materialization=on,in_to_exists=off,semijoin=off,partial_match_rowid_merge=off,partial_match_table_scan=off,subquery_cache=off,mrr=on,mrr_cost_based=on,mrr_sort_keys=on,outer_join_with_cache=off,semijoin_with_cache=off,join_cache_incremental=off,join_cache_hashed=off,join_cache_bka=off,optimize_join_buffer_size=on,table_elimination=off,extended_keys=off,exists_to_in=off,orderby_uses_equalities=off,condition_pushdown_for_derived=off,split_materialized=on,condition_pushdown_for_subquery=on,rowid_filter=on,condition_pushdown_from_having=on,not_null_range_scan=off,hash_join_cardinality=off
 
 Warnings:
 Warning	1681	'engine_condition_pushdown=on' is deprecated and will be removed in a future release

mysql-test/suite/sys_vars/r/sysvars_server_embedded.result

@@ -2299,7 +2299,7 @@ VARIABLE_COMMENT	Fine-tune the optimizer behavior
 NUMERIC_MIN_VALUE	NULL
 NUMERIC_MAX_VALUE	NULL
 NUMERIC_BLOCK_SIZE	NULL
-ENUM_VALUE_LIST	index_merge,index_merge_union,index_merge_sort_union,index_merge_intersection,index_merge_sort_intersection,engine_condition_pushdown,index_condition_pushdown,derived_merge,derived_with_keys,firstmatch,loosescan,materialization,in_to_exists,semijoin,partial_match_rowid_merge,partial_match_table_scan,subquery_cache,mrr,mrr_cost_based,mrr_sort_keys,outer_join_with_cache,semijoin_with_cache,join_cache_incremental,join_cache_hashed,join_cache_bka,optimize_join_buffer_size,table_elimination,extended_keys,exists_to_in,orderby_uses_equalities,condition_pushdown_for_derived,split_materialized,condition_pushdown_for_subquery,rowid_filter,condition_pushdown_from_having,not_null_range_scan,default
+ENUM_VALUE_LIST	index_merge,index_merge_union,index_merge_sort_union,index_merge_intersection,index_merge_sort_intersection,engine_condition_pushdown,index_condition_pushdown,derived_merge,derived_with_keys,firstmatch,loosescan,materialization,in_to_exists,semijoin,partial_match_rowid_merge,partial_match_table_scan,subquery_cache,mrr,mrr_cost_based,mrr_sort_keys,outer_join_with_cache,semijoin_with_cache,join_cache_incremental,join_cache_hashed,join_cache_bka,optimize_join_buffer_size,table_elimination,extended_keys,exists_to_in,orderby_uses_equalities,condition_pushdown_for_derived,split_materialized,condition_pushdown_for_subquery,rowid_filter,condition_pushdown_from_having,not_null_range_scan,hash_join_cardinality,default
 READ_ONLY	NO
 COMMAND_LINE_ARGUMENT	REQUIRED
 VARIABLE_NAME	OPTIMIZER_TRACE

mysql-test/suite/sys_vars/r/sysvars_server_notembedded.result

@@ -2459,7 +2459,7 @@ VARIABLE_COMMENT	Fine-tune the optimizer behavior
 NUMERIC_MIN_VALUE	NULL
 NUMERIC_MAX_VALUE	NULL
 NUMERIC_BLOCK_SIZE	NULL
-ENUM_VALUE_LIST	index_merge,index_merge_union,index_merge_sort_union,index_merge_intersection,index_merge_sort_intersection,engine_condition_pushdown,index_condition_pushdown,derived_merge,derived_with_keys,firstmatch,loosescan,materialization,in_to_exists,semijoin,partial_match_rowid_merge,partial_match_table_scan,subquery_cache,mrr,mrr_cost_based,mrr_sort_keys,outer_join_with_cache,semijoin_with_cache,join_cache_incremental,join_cache_hashed,join_cache_bka,optimize_join_buffer_size,table_elimination,extended_keys,exists_to_in,orderby_uses_equalities,condition_pushdown_for_derived,split_materialized,condition_pushdown_for_subquery,rowid_filter,condition_pushdown_from_having,not_null_range_scan,default
+ENUM_VALUE_LIST	index_merge,index_merge_union,index_merge_sort_union,index_merge_intersection,index_merge_sort_intersection,engine_condition_pushdown,index_condition_pushdown,derived_merge,derived_with_keys,firstmatch,loosescan,materialization,in_to_exists,semijoin,partial_match_rowid_merge,partial_match_table_scan,subquery_cache,mrr,mrr_cost_based,mrr_sort_keys,outer_join_with_cache,semijoin_with_cache,join_cache_incremental,join_cache_hashed,join_cache_bka,optimize_join_buffer_size,table_elimination,extended_keys,exists_to_in,orderby_uses_equalities,condition_pushdown_for_derived,split_materialized,condition_pushdown_for_subquery,rowid_filter,condition_pushdown_from_having,not_null_range_scan,hash_join_cardinality,default
 READ_ONLY	NO
 COMMAND_LINE_ARGUMENT	REQUIRED
 VARIABLE_NAME	OPTIMIZER_TRACE

sql/sql_priv.h

@@ -234,6 +234,7 @@
 #define OPTIMIZER_SWITCH_USE_ROWID_FILTER          (1ULL << 33)
 #define OPTIMIZER_SWITCH_COND_PUSHDOWN_FROM_HAVING (1ULL << 34)
 #define OPTIMIZER_SWITCH_NOT_NULL_RANGE_SCAN       (1ULL << 35)
+#define OPTIMIZER_SWITCH_HASH_JOIN_CARDINALITY     (1ULL << 36)
 
 #define OPTIMIZER_SWITCH_DEFAULT   (OPTIMIZER_SWITCH_INDEX_MERGE | \
                                     OPTIMIZER_SWITCH_INDEX_MERGE_UNION | \

sql/sys_vars.cc

@@ -2756,6 +2756,7 @@ export const char *optimizer_switch_names[]=
   "rowid_filter",
   "condition_pushdown_from_having",
   "not_null_range_scan",
+  "hash_join_cardinality",
   "default", 
   NullS
 };