Or, The Transaction Log: Why You Can’t Run Your Database Without It
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ACID Properties
Transactions
Write-ahead Logging
Log Space Reservation
Reading the Log with fn_dblog
Identifying Active Transactions
Finding Log Records Associated with Active
Transactions
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Atomicity
Consistency
Isolation
Durability
Human sacrifice, dogs and cats living
together... mass hysteria!
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What is a transaction?
Explicit v. Implicit Transactions
Write-ahead logging
Roll back and roll forward
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SQL Server uses log space for transaction
records
Additional space is reserved for potential
rollback activity
Committed transaction releases reserved
space
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SMALLER TRANSACTIONS ARE BETTER!
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Table-based function that allows the
transaction log to be read
Takes 2 parameters, starting and ending log
sequence numbers (LSN)
SELECT * FROM fn_dblog(NULL,NULL)
returns the contents of the log
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Returns information about active
transactions
Results contain the begin and end LSN for
each transaction
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Both the DMV and function contain a
transaction_id
The DMV id is hexadecimal and the function
id is decimal, so converting one of them
should work, right?
Image Source - http://4.bp.blogspot.com/DY_k_dCp9EE/TvzOLaf17JI/AAAAAAAABBM/dBff_mOtNws/s1600/wrong+answer.jpg
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Converting the transaction IDs from either
source did not result in a match
After several attempts to make it work (octal,
double and add 30, multiply by 9/5 and add
32) I wrote Paul Randal
His response? “They don’t match. It’s
annoying.”
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Both the DMV and the function contain begin
and end LSNs
The function returns colon-delimited hex
LSNs (0000001a:000027a5:0001)
The DMV returns a decimal value
(26000001014900001)