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The aim of the InnoDB change buffer is to avoid delays when a leaf page of a secondary index is not present in the buffer pool, and a record needs to be inserted, delete-marked, or purged. Instead of reading the page into the buffer pool for making such a modification, we may insert a record to the change buffer (a special index tree in the InnoDB system tablespace). The buffered changes are guaranteed to be merged if the index page actually needs to be read later. The change buffer could be useful when the database is stored on a rotational medium (hard disk) where random seeks are slower than sequential reads or writes. Obviously, the change buffer will cause write amplification, due to potentially large amount of metadata that is being written to the change buffer. We will have to write redo log records for modifying the change buffer tree as well as the user tablespace. Furthermore, in the user tablespace, we must maintain a change buffer bitmap page that uses 2 bits for estimating the amount of free space in pages, and 1 bit to specify whether buffered changes exist. This bitmap needs to be updated on every operation, which could reduce performance. Even if the change buffer were free of bugs such as MDEV-24449 (potentially causing the corruption of any page in the system tablespace) or MDEV-26977 (corruption of secondary indexes due to a currently unknown reason), it will make diagnosis of other data corruption harder. Because of all this, it is best to disable the change buffer by default.
55 lines
1.5 KiB
Text
55 lines
1.5 KiB
Text
#
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# Bug#69122 - INNODB DOESN'T REDO-LOG INSERT BUFFER MERGE
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# OPERATION IF IT IS DONE IN-PLACE
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#
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call mtr.add_suppression("InnoDB: innodb_read_only prevents crash recovery");
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call mtr.add_suppression("Plugin initialization aborted at srv0start\\.cc");
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call mtr.add_suppression("Plugin 'InnoDB'");
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FLUSH TABLES;
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CREATE TABLE t1(
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a INT AUTO_INCREMENT PRIMARY KEY,
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b CHAR(1),
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c INT,
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INDEX(b))
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ENGINE=InnoDB STATS_PERSISTENT=0;
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SET GLOBAL innodb_change_buffering_debug = 1;
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SET GLOBAL innodb_change_buffering = all;
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INSERT INTO t1 SELECT 0,'x',1 FROM seq_1_to_8192;
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BEGIN;
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SELECT b FROM t1 LIMIT 3;
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b
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x
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x
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x
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connect con1,localhost,root,,;
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BEGIN;
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DELETE FROM t1 WHERE a=1;
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INSERT INTO t1 VALUES(1,'X',1);
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SET DEBUG_DBUG='+d,crash_after_log_ibuf_upd_inplace';
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SELECT b FROM t1 LIMIT 3;
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ERROR HY000: Lost connection to MySQL server during query
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disconnect con1;
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connection default;
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FOUND 1 /Wrote log record for ibuf update in place operation/ in mysqld.1.err
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# restart: --innodb-read-only
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CHECK TABLE t1;
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Table Op Msg_type Msg_text
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test.t1 check Error Unknown storage engine 'InnoDB'
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test.t1 check error Corrupt
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FOUND 1 /innodb_read_only prevents crash recovery/ in mysqld.1.err
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# restart: --innodb-force-recovery=5
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SELECT * FROM t1 LIMIT 1;
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a b c
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1 X 1
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SHOW ENGINE INNODB STATUS;
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Type Name Status
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InnoDB insert 0, delete mark 0
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SET GLOBAL innodb_fast_shutdown=0;
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# restart
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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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SHOW ENGINE INNODB STATUS;
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Type Name Status
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InnoDB
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DROP TABLE t1;
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