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Displaying posts with tag: redo (reset)

Redo Logging in InnoDB
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Introduction

InnoDB is a general-purpose storage engine that balances high reliability and high performance. It is a transactional storage engine and is fully ACID compliant, as would be expected from any relational database. The durability guarantee provided by InnoDB is made possible by the redo logs.

This article will provide an overview of the redo log subsystem or log subsystem of InnoDB. We will look at the following details:

  • The global log system object, which provides access to important data structures and information.
  • The mini-transaction (mtr), using which all redo log records are created.
  • The global in-memory log buffer (or just log buffer), into which the redo logs are written to from the mini
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InnoDB logfiles
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The unsung heroes of InnoDB are the logfiles. They are what makes InnoDB automatic crash recovery possible.

Database administrators of other DBMS may be familiar with the concept of a “redo” log. When data is changed, affected data pages are changed in the innodb_buffer_pool. Then, the change is written to the redo log, which in MySQL is the InnoDB logfile (ib_logfile0 and ib_logfile1). The pages are marked as “dirty”, and eventually get flushed and written to disk.

If MySQL crashes, there may be data that is changed that has not been written to disk. Those data pages were marked as “dirty” in the innodb_buffer_pool, but after a MySQL crash the innodb_buffer_pool no longer exists. However, they were written to the redo log. On crash recovery, MySQL can read the redo log (InnoDB log files) and apply any changes that were not written to

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Oracle Standby Recovery Rate Monitoring
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So you have created your standby database using the RMAN DUPLICATE command, you have set the ARCHIVE_LAG_TARGET to maintain a minimum lag target, and you have sorted out those nasty datafile missing errors using automatic file management. You’ve even added standby redo logs to improve the Mean Time To Recovery (MTTR). Now management are demanding [...]
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