MDEV-32351 Significant slowdown for query with many outer joins
This patch fixes a performance regression introduced in the patch for the bug MDEV-21104. The performance regression could affect queries for which join buffer was used for an outer join such that its on expression from which a conjunctive condition depended only on outer tables can be extracted. If the number of records in the join buffer for which this condition was false greatly exceeded the number of other records the slowdown could be significant. If there is a conjunctive condition extracted from the ON expression depending only on outer tables this condition is evaluated when interesting fields of each survived record of outer tables are put into the join buffer. Each such set of fields for any join operation is supplied with a match flag field used to generate null complemented rows. If the result of the evaluation of the condition is false the flag is set to MATCH_IMPOSSIBLE. When looking in the join buffer for records matching a record of the right operand of the outer join operation the records with such flags are not needed to be unpacked into record buffers for evaluation of on expressions. The patch for MDEV-21104 fixing some problem of wrong results when 'not exists' optimization by mistake broke the code that allowed to ignore records with the match flag set to MATCH_IMPOSSIBLE when looking for matching records. As a result such records were unpacked for each record of the right operand of the outer join operation. This caused significant execution penalty in some cases. One of the test cases added in the patch can be used only for demonstration of the restored performance for the reported query. The second test case is needed to demonstrate the validity of the fix.
This commit is contained in:
Igor Babaev
Oleksandr Byelkin
parent
11abc21911
commit
954a6decd4
@ -6270,5 +6270,131 @@ ERROR HY001: Could not create a join buffer. Please check and adjust the value o
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SET JOIN_buffer_size=16384;
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SELECT * FROM information_schema.statistics JOIN information_schema.COLUMNS USING (table_name,column_name);
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#
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# MDEV-32351: Join buffer used for outer join with ON condition
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# depending only on outer tables
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#
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CREATE TABLE t1 (b int NOT NULL, PRIMARY KEY (b)) ENGINE=MYISAM;
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INSERT INTO t1 select seq from seq_1_to_10000;
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CREATE TABLE t2 (b int NOT NULL, d varchar(255), KEY (b)) ENGINE=MYISAM ;
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INSERT INTO t2 VALUES (1,1),(2,2),(3,3);
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CREATE TABLE t3 (c int NOT NULL, PRIMARY KEY (c)) ENGINE=MYISAM ;
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INSERT INTO t3 select seq from seq_1_to_3000;
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CREATE TABLE t4 (c int NOT NULL, PRIMARY KEY (c)) ENGINE=MYISAM;
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INSERT INTO t4 select seq from seq_1_to_3000;
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ANALYZE TABLE t1,t2,t3,t4;
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Table Op Msg_type Msg_text
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test.t1 analyze status Engine-independent statistics collected
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test.t1 analyze status OK
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test.t2 analyze status Engine-independent statistics collected
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test.t2 analyze status OK
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test.t3 analyze status Engine-independent statistics collected
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test.t3 analyze status OK
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test.t4 analyze status Engine-independent statistics collected
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test.t4 analyze status OK
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set join_cache_level=0;
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EXPLAIN SELECT COUNT(*)
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FROM t1
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LEFT JOIN t2 ON t1.b = t2.b
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LEFT JOIN t3 ON t2.d = t3.c
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LEFT JOIN t4 ON t3.c=1;
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE t1 index NULL PRIMARY 4 NULL 10000 Using index
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1 SIMPLE t2 ref b b 4 test.t1.b 1
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1 SIMPLE t3 eq_ref PRIMARY PRIMARY 4 test.t2.d 1 Using where; Using index
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1 SIMPLE t4 index NULL PRIMARY 4 NULL 3000 Using where; Using index
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SELECT COUNT(*)
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FROM t1
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LEFT JOIN t2 ON t1.b = t2.b
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LEFT JOIN t3 ON t2.d = t3.c
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LEFT JOIN t4 ON t3.c=1;
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COUNT(*)
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12999
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set join_cache_level=default;
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EXPLAIN SELECT COUNT(*)
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FROM t1
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LEFT JOIN t2 ON t1.b = t2.b
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LEFT JOIN t3 ON t2.d = t3.c
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LEFT JOIN t4 ON t3.c=1;
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE t1 index NULL PRIMARY 4 NULL 10000 Using index
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1 SIMPLE t2 ref b b 4 test.t1.b 1
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1 SIMPLE t3 eq_ref PRIMARY PRIMARY 4 test.t2.d 1 Using where; Using index
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1 SIMPLE t4 index NULL PRIMARY 4 NULL 3000 Using where; Using index; Using join buffer (flat, BNL join)
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SELECT COUNT(*)
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FROM t1
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LEFT JOIN t2 ON t1.b = t2.b
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LEFT JOIN t3 ON t2.d = t3.c
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LEFT JOIN t4 ON t3.c=1;
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COUNT(*)
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12999
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DROP TABLE t1,t2,t3,t4;
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CREATE TABLE t1 (b int NOT NULL, PRIMARY KEY (b));
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INSERT INTO t1 select seq from seq_1_to_10;
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CREATE TABLE t2 (b int NOT NULL, d varchar(255), KEY (b)) ;
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INSERT INTO t2 VALUES (1,1),(2,2),(3,3);
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CREATE TABLE t3 (c int NOT NULL, PRIMARY KEY (c)) ;
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INSERT INTO t3 select seq from seq_1_to_3;
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CREATE TABLE t4 (c int NOT NULL, PRIMARY KEY (c)) ;
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INSERT INTO t4 select seq from seq_1_to_3;
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set join_cache_level=0;
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EXPLAIN SELECT *
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FROM t1
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LEFT JOIN t2 ON t1.b = t2.b
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LEFT JOIN t3 ON t2.d = t3.c
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LEFT JOIN t4 ON t3.c=1;
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE t1 index NULL PRIMARY 4 NULL 10 Using index
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1 SIMPLE t2 ALL b NULL NULL NULL 3 Using where
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1 SIMPLE t3 eq_ref PRIMARY PRIMARY 4 test.t2.d 1 Using where; Using index
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1 SIMPLE t4 index NULL PRIMARY 4 NULL 3 Using where; Using index
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SELECT *
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FROM t1
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LEFT JOIN t2 ON t1.b = t2.b
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LEFT JOIN t3 ON t2.d = t3.c
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LEFT JOIN t4 ON t3.c=1;
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b b d c c
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1 1 1 1 1
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1 1 1 1 2
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1 1 1 1 3
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2 2 2 2 NULL
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3 3 3 3 NULL
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4 NULL NULL NULL NULL
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5 NULL NULL NULL NULL
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6 NULL NULL NULL NULL
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7 NULL NULL NULL NULL
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8 NULL NULL NULL NULL
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9 NULL NULL NULL NULL
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10 NULL NULL NULL NULL
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set join_cache_level=default;
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EXPLAIN SELECT *
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FROM t1
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LEFT JOIN t2 ON t1.b = t2.b
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LEFT JOIN t3 ON t2.d = t3.c
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LEFT JOIN t4 ON t3.c=1;
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE t1 index NULL PRIMARY 4 NULL 10 Using index
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1 SIMPLE t2 ALL b NULL NULL NULL 3 Using where; Using join buffer (flat, BNL join)
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1 SIMPLE t3 eq_ref PRIMARY PRIMARY 4 test.t2.d 1 Using where; Using index
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1 SIMPLE t4 index NULL PRIMARY 4 NULL 3 Using where; Using index; Using join buffer (flat, BNL join)
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SELECT *
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FROM t1
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LEFT JOIN t2 ON t1.b = t2.b
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LEFT JOIN t3 ON t2.d = t3.c
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LEFT JOIN t4 ON t3.c=1;
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b b d c c
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1 1 1 1 1
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1 1 1 1 2
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1 1 1 1 3
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2 2 2 2 NULL
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3 3 3 3 NULL
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4 NULL NULL NULL NULL
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5 NULL NULL NULL NULL
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6 NULL NULL NULL NULL
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7 NULL NULL NULL NULL
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8 NULL NULL NULL NULL
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9 NULL NULL NULL NULL
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10 NULL NULL NULL NULL
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DROP TABLE t1,t2,t3,t4;
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#
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# End of 10.4 tests
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#
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@ -4247,6 +4247,64 @@ SET JOIN_buffer_size=16384;
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SELECT * FROM information_schema.statistics JOIN information_schema.COLUMNS USING (table_name,column_name);
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--enable_result_log
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--echo #
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--echo # MDEV-32351: Join buffer used for outer join with ON condition
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--echo # depending only on outer tables
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--echo #
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--source include/have_sequence.inc
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CREATE TABLE t1 (b int NOT NULL, PRIMARY KEY (b)) ENGINE=MYISAM;
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INSERT INTO t1 select seq from seq_1_to_10000;
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CREATE TABLE t2 (b int NOT NULL, d varchar(255), KEY (b)) ENGINE=MYISAM ;
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INSERT INTO t2 VALUES (1,1),(2,2),(3,3);
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CREATE TABLE t3 (c int NOT NULL, PRIMARY KEY (c)) ENGINE=MYISAM ;
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INSERT INTO t3 select seq from seq_1_to_3000;
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CREATE TABLE t4 (c int NOT NULL, PRIMARY KEY (c)) ENGINE=MYISAM;
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INSERT INTO t4 select seq from seq_1_to_3000;
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ANALYZE TABLE t1,t2,t3,t4;
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let $q1=
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SELECT COUNT(*)
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FROM t1
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LEFT JOIN t2 ON t1.b = t2.b
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LEFT JOIN t3 ON t2.d = t3.c
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LEFT JOIN t4 ON t3.c=1;
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set join_cache_level=0;
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eval EXPLAIN $q1;
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eval $q1;
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set join_cache_level=default;
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eval EXPLAIN $q1;
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eval $q1;
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DROP TABLE t1,t2,t3,t4;
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CREATE TABLE t1 (b int NOT NULL, PRIMARY KEY (b));
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INSERT INTO t1 select seq from seq_1_to_10;
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CREATE TABLE t2 (b int NOT NULL, d varchar(255), KEY (b)) ;
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INSERT INTO t2 VALUES (1,1),(2,2),(3,3);
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CREATE TABLE t3 (c int NOT NULL, PRIMARY KEY (c)) ;
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INSERT INTO t3 select seq from seq_1_to_3;
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CREATE TABLE t4 (c int NOT NULL, PRIMARY KEY (c)) ;
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INSERT INTO t4 select seq from seq_1_to_3;
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let $q2=
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SELECT *
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FROM t1
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LEFT JOIN t2 ON t1.b = t2.b
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LEFT JOIN t3 ON t2.d = t3.c
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LEFT JOIN t4 ON t3.c=1;
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set join_cache_level=0;
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eval EXPLAIN $q2;
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eval $q2;
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set join_cache_level=default;
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eval EXPLAIN $q2;
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eval $q2;
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DROP TABLE t1,t2,t3,t4;
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--echo #
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--echo # End of 10.4 tests
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--echo #
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@ -2054,10 +2054,11 @@ bool JOIN_CACHE::skip_if_matched()
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- In the case of a semi-nest the match flag may be in two states
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{MATCH_NOT_FOUND, MATCH_FOUND}. The record is skipped if the flag is set
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to MATCH_FOUND.
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- In the case of a outer join nest when not_exists optimization is applied
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the match may be in three states {MATCH_NOT_FOUND, MATCH_IMPOSSIBLE,
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MATCH_FOUND. The record is skipped if the flag is set to MATCH_FOUND or
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to MATCH_IMPOSSIBLE.
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- In the case of an outer join the match may be in three states
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{MATCH_NOT_FOUND, MATCH_IMPOSSIBLE, MATCH_FOUND}.
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If not_exists optimization is applied the record is skipped when
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the flag is set to MATCH_FOUND or to MATCH_IMPOSSIBLE. Otherwise
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the record is skipped only when the flag is set to MATCH_IMPOSSIBLE.
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If the record is skipped the value of 'pos' is set to point to the position
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right after the record.
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@ -2080,13 +2081,13 @@ bool JOIN_CACHE::skip_if_not_needed_match()
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if (prev_cache)
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offset+= prev_cache->get_size_of_rec_offset();
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if (!join_tab->check_only_first_match())
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return FALSE;
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match_fl= get_match_flag_by_pos(pos+offset);
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skip= join_tab->first_sj_inner_tab ?
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match_fl == MATCH_FOUND : // the case of semi-join
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match_fl != MATCH_NOT_FOUND; // the case of outer-join
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match_fl == MATCH_FOUND : // the case of semi-join
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not_exists_opt_is_applicable &&
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join_tab->table->reginfo.not_exists_optimize ?
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match_fl != MATCH_NOT_FOUND : // the case of not exist opt
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match_fl == MATCH_IMPOSSIBLE;
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if (skip)
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{
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@ -2383,7 +2384,7 @@ enum_nested_loop_state JOIN_CACHE::join_matching_records(bool skip_last)
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as candidates for matches.
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*/
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bool not_exists_opt_is_applicable= true;
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not_exists_opt_is_applicable= true;
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if (check_only_first_match && join_tab->first_inner)
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{
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/*
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@ -2408,8 +2409,9 @@ enum_nested_loop_state JOIN_CACHE::join_matching_records(bool skip_last)
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}
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}
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if (!check_only_first_match ||
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(join_tab->first_inner && !not_exists_opt_is_applicable) ||
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if ((!join_tab->on_precond &&
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(!check_only_first_match ||
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(join_tab->first_inner && !not_exists_opt_is_applicable))) ||
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!skip_next_candidate_for_match(rec_ptr))
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{
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read_next_candidate_for_match(rec_ptr);
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@ -340,6 +340,9 @@ protected:
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/* The length of an embedded key value */
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uint emb_key_length;
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/* This flag is used only when 'not exists' optimization can be applied */
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bool not_exists_opt_is_applicable;
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/*
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This object provides the methods to iterate over records of
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the joined table join_tab when looking for join matches between
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@ -536,6 +539,7 @@ protected:
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prev_cache= next_cache= 0;
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buff= 0;
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min_buff_size= max_buff_size= 0; // Caches
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not_exists_opt_is_applicable= false;
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}
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/*
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