Sql checksum code#
WHERE db.page_verify_option_desc N 'CHECKSUM' Īfter you run this query, you can copy the rows from your results grid in SSMS to a new query window, and then run your ALTER DATABASE statements when you are ready, without having to write all of the T-SQL code yourself. If you have a large number of databases that need to be changed, you can write a query to generate the ALTER DATABASE statements for you, like this: - Generate ALTER DATABASE statements to change Page Verify option to CHECKSUM SELECT N 'ALTER DATABASE SET PAGE_VERIFY CHECKSUM WITH NO_WAIT ' FROM sys.databases AS db GO ALTER DATABASE SET PAGE_VERIFY CHECKSUM WITH NO_WAIT
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If you have just a few databases, it is pretty easy to run code like this for each one, to change this option: - T-SQL to change Page Verify option to CHECKSUM for a single database USE You can easily query sys.databases to find out the status of the Page Verify database option for all of your databases with this query: - Get value of page verify option for all databases SELECT name, page_verify_option_desc In my opinion, all of your databases should be using CHECKSUM for their Page Verify database option. Kendra Little wrote a good post that demonstrates how CHECKSUM reacts to corruption here. Paul Randal talked about some of the myths around page verify here. This helps provide a high level of data-file integrity.” When the page is read from disk, the checksum is recomputed and compared to the checksum value that is stored in the page header. I also run into instances where people have changed the Page Verify database option to NONE, thinking that this would have a dramatic beneficial effect on performance (which is not true).įrom BOL: “When CHECKSUM is enabled for the PAGE_VERIFY database option, the SQL Server Database Engine calculates a checksum over the contents of the whole page, and stores the value in the page header when a page is written to disk.
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The most common reason for this is that an older database that was originally created in SQL Server 2000 or older was upgraded to SQL Server 2005 or newer, and the Page Verify Option was left at the older and less effective TORN_PAGE value. no statistics are kept which might affect resultsĬOALESCE(b., CAST(0 AS DECIMAL(36, 12))) != COALESCE(a., CAST(0 AS DECIMAL(36, 12)))Ĭast(COALESCE(a., CAST('' as datetime)) as varchar)Ĭast(COALESCE(a., CAST(0 AS DECIMAL(18, 2))) as varchar)Ĭast(COALESCE(a., 0) as varchar)Ĭast(COALESCE(b., CAST('' as datetime)) as varchar)Ĭast(COALESCE(b., CAST(0 AS DECIMAL(18, 2))) as varchar)Ĭast(COALESCE(b., 0) as varchar) drop the tables to also ensure nothing's cached and
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SELECT 'Finished', 'Time To Run: ' + CAST(DATEDIFF(SECOND, as varchar) + ' seconds' This is the code that varies between techniques. , = b.įROM AAA_DAVE_TEST_Target a inner join b
Sql checksum update#
ensure there are differences so an update has to be performed insert 20,000,000 records into the second table insert 20,000,000 records into the first table Only used for the test with the checksum column added
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)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON IF NOT EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'') AND type in (N'U'))ĬONSTRAINT PRIMARY KEY CLUSTERED Surely there must be a better, faster way to do this?ĬOALESCE(b.,'') != COALESCE(a.,'')ĬOALESCE(b.,CAST(0 ASDECIMAL(38, 12))) != COALESCE(a.,CAST(0 ASDECIMAL(38, 12)))ĬOALESCE(b., 0) != COALESCE(a., 0)