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It is not safe to invoke trx_purge_free_segment() or execute innodb_undo_log_truncate=ON before all undo log records in the rollback segment has been processed. A prominent failure that would occur due to premature freeing of undo log pages is that trx_undo_get_undo_rec() would crash when trying to copy an undo log record to fetch the previous version of a record. If trx_undo_get_undo_rec() was not invoked in the unlucky time frame, then the symptom would be that some committed transaction history is never removed. This would be detected by CHECK TABLE...EXTENDED that was impleented in commit ab0190101b0587e0e03b2d75a967050b9a85fd1b. Such a garbage collection leak should be possible even when using innodb_undo_log_truncate=OFF, just involving trx_purge_free_segment(). trx_rseg_t::needs_purge: Change the type from Boolean to a transaction identifier, noting the most recent non-purged transaction, or 0 if everything has been purged. On transaction start, we initialize this to 1 more than the transaction start ID. On recovery, the field may be adjusted to the transaction end ID (TRX_UNDO_TRX_NO) if it is larger. The field TRX_UNDO_NEEDS_PURGE becomes write-only; only some debug assertions that would validate the value. The field reflects the old inaccurate Boolean field trx_rseg_t::needs_purge. trx_undo_mem_create_at_db_start(), trx_undo_lists_init(), trx_rseg_mem_restore(): Remove the parameter max_trx_id. Instead, store the maximum in trx_rseg_t::needs_purge, where trx_rseg_array_init() will find it. trx_purge_free_segment(): Contiguously hold a lock on trx_rseg_t to prevent any concurrent allocation of undo log. trx_purge_truncate_rseg_history(): Only invoke trx_purge_free_segment() if the rollback segment is empty and there are no pending transactions associated with it. trx_purge_truncate_history(): Only proceed with innodb_undo_log_truncate=ON if trx_rseg_t::needs_purge indicates that all history has been purged. Tested by: Matthias Leich
91 lines
2.1 KiB
Plaintext
91 lines
2.1 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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SET @saved_frequency= @@GLOBAL.innodb_purge_rseg_truncate_frequency;
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SET GLOBAL innodb_purge_rseg_truncate_frequency= 1;
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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 STATS_PERSISTENT=0;
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InnoDB 0 transactions not purged
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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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BEGIN;
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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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BEGIN;
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CALL insert_n(51, 100);;
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connection con2;
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COMMIT;
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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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COMMIT;
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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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InnoDB 2 transactions not purged
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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 IF(@num_pages_2 - @num_pages_1 < 5000, 'OK', @num_pages_2 - @num_pages_1) num_pages_diff;
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num_pages_diff
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OK
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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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SET GLOBAL innodb_purge_rseg_truncate_frequency= @saved_frequency;
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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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