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Transaction logs Exchange 2003

Posted on 2010-09-01
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Hello EE's

Please provide me a laymans term definition of the types of transaction logs in Exchange 2003. How they operate when email is composed, their size, etc.

Thanks
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Question by:lazik
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by:BGilhooley
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Hi there,

Have a read of this, nice explanation with some best practices thrown in:

http://www.msexchange.org/articles/Transaction-Logs-Lifeblood-Exchange.html

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MojoTech earned 500 total points
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Transaction logs are basically a temporary location for data before it gets commited (written) to the database, so for example an email comes in and it will go to a log file, when the database is free/available that log file will get written to the databse.

In regards to backing up and restoring exchange this is why you need the database and the log files, becausr together they will contain all the emails your org has recieved.
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by:Shreedhar Ette
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by:Mkris9
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This is from msexchange.org article

The transaction logs are some of the most crucial files when it comes to a working Exchange server. Microsoft Exchange Server uses transaction logs as a disaster recovery method that can bring a Exchange database back to a consistent state after a crash. Before anything is written to the EDB file, it is first written to a transaction log. Once the transaction has been logged, the data is written to the database when convenient.

Until a transaction is committed to the database, it is available from memory and recorded in the transaction logs. This is why you will see store.exe use up to 1GB of memory after the Exchange server has been in use for a while. After an Exchange server is brought back up after a crash, the checkpoint file points to the last committed transaction in the transaction logs which are then replayed from that point on. This form of write-ahead logging is important for you to know.  

There are four types of transaction logs:

E##.log is the current transaction log for the database.  Once the log file reaches 5MB in size it is renamed E#######.log and a new E##.log is created.  As with the checkpoint file the ## represents the Storage Group identifier.  While the new E##.log file is being created you will see a file called Edbtmp.log which is a template for Exchange server log files.
E#######.log are the secondary transaction logs.  They are numbered sequentially starting with E0000001.log using the hexadecimal numbering format and are 5MB in size.
Res1.log is a reserved log file that is limited to 5MB in size.  When the disk has run out of space, transactions are written to this log file while you work on clearing up space on the disk.
Res2.log is another reserved log with the same function as Res1.log.
Transaction logs can grow at a fast pace as each and every transaction is recorded to the log files. There are two ways to manage this growth with the recommended method being a regular full backup of the Information Store. Upon successful backup, the transactions are committed to the database and then purged.  

The other method is to enable circular logging. Circular logging is disabled by default as it only allows you to recover Exchange data since the last full backup. With circular logging enabled the transaction logs are purged as the transactions are committed to the database. If you have to restore from backup, the transaction logs will not be replayed and all transactions since that backup will be lost.

The two reserved log files, Res1.log and Res2.log, are used to “save” 10MB of space on the disk in case there is no more free space. When the disk runs out of free space, the transactions are logged to the reserve logs as the Information Store shuts down gracefully. You will not be able to restart the Information Store service until you clear up some disk space.
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