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If there're multiple row versions in InnoDB, reading one row from PK may have O(N) complexity and reading from secondary keys may have O(N^2) complexity. The problem occurs when there are many pending versions of the same row, meaning that the primary key is the same, but a secondary key is different. The slowdown occurs when the secondary index is traversed. This patch creates a helper class for the function row_sel_get_clust_rec_for_mysql() which can remember and re-use cached_clust_rec & cached_old_vers so that rec_get_offsets() does not need to be called over and over for the clustered record. Corrections by Kevin Lewis <kevin.lewis@oracle.com> MDEV-20341 Unstable innodb.innodb_bug14704286 Removed test that tested the ability of interrupting long query which is not long anymore.
82 lines
1.8 KiB
Plaintext
82 lines
1.8 KiB
Plaintext
#
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# Bug #84958 InnoDB's MVCC has O(N^2) behaviors
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# https://bugs.mysql.com/bug.php?id=84958
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#
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# Set up the test with a procedure and a function.
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#
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CREATE PROCEDURE insert_n(start int, end int)
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BEGIN
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DECLARE i INT DEFAULT start;
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WHILE i <= end do
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INSERT INTO t1 VALUES (1, 2, 3) ON DUPLICATE KEY UPDATE c = i;
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SET i = i + 1;
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END WHILE;
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END~~
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CREATE FUNCTION num_pages_get()
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RETURNS INT
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BEGIN
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DECLARE ret INT;
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SELECT variable_value INTO ret
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FROM information_schema.global_status
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WHERE variable_name = 'innodb_buffer_pool_read_requests';
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RETURN ret;
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END~~
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#
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# Create a table with one record in it and start an RR transaction
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#
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CREATE TABLE t1 (a INT, b INT, c INT, PRIMARY KEY(a,b), KEY (b,c))
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ENGINE=InnoDB;
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BEGIN;
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SELECT * FROM t1;
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a b c
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#
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# Create 100 newer record versions in con2 and con3
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#
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connect con2, localhost, root,,;
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connection con2;
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INSERT INTO t1 VALUES (1, 2, 3) ON DUPLICATE KEY UPDATE c = NULL;
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CALL insert_n(1, 50);;
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connect con3, localhost, root,,;
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connection con3;
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CALL insert_n(51, 100);;
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connection con2;
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connection con3;
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INSERT INTO t1 VALUES (1, 2, 1) ON DUPLICATE KEY UPDATE c = NULL;
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connection default;
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#
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# Connect to default and record how many pages were accessed
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# when selecting the record using the secondary key.
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#
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SET @num_pages_1 = num_pages_get();
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SELECT * FROM t1 force index (b);
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a b c
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SET @num_pages_2= num_pages_get();
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SELECT @num_pages_2 - @num_pages_1 < 500;
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@num_pages_2 - @num_pages_1 < 500
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1
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#
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# Commit and show the final record.
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#
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SELECT * FROM t1;
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a b c
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SELECT * FROM t1 force index (b);
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a b c
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COMMIT;
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SELECT * FROM t1 force index (b);
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a b c
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1 2 NULL
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SELECT * FROM t1;
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a b c
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1 2 NULL
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CHECK TABLE t1;
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Table Op Msg_type Msg_text
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test.t1 check status OK
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#
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# Cleanup
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#
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disconnect con2;
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disconnect con3;
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DROP TABLE t1;
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DROP PROCEDURE insert_n;
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DROP FUNCTION num_pages_get;
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