SQL Server 2012 Column Identity Increment Jumping from 6 to 1000+ on 7Th Entry

SQL Server 2012 column identity increment jumping from 6 to 1000+ on 7th entry

This is all perfectly normal. Microsoft added sequences in SQL Server 2012, finally, i might add and changed the way identity keys are generated. Have a look here for some explanation.

If you want to have the old behaviour, you can:

  1. use trace flag 272 - this will cause a log record to be generated for each generated identity value. The performance of identity generation may be impacted by turning on this trace flag.
  2. use a sequence generator with the NO CACHE setting (http://msdn.microsoft.com/en-us/library/ff878091.aspx)

Identity increment is jumping in SQL Server database

You are encountering this behaviour due to a performance improvement since SQL Server 2012.

It now by default uses a cache size of 1,000 when allocating IDENTITY values for an int column and restarting the service can "lose" unused values (The cache size is 10,000 for bigint/numeric).

This is mentioned in the documentation

SQL Server might cache identity values for performance reasons and
some of the assigned values can be lost during a database failure or
server restart. This can result in gaps in the identity value upon
insert. If gaps are not acceptable then the application should use its
own mechanism to generate key values. Using a sequence generator with
the NOCACHE option can limit the gaps to transactions that are never
committed.

From the data you have shown it looks like this happened after the data entry for 22 December then when it restarted SQL Server reserved the values 1206306 - 1207305. After data entry for 24 - 25 December was done another restart and SQL Server reserved the next range 1207306 - 1208305 visible in the entries for the 28th.

Unless you are restarting the service with unusual frequency any "lost" values are unlikely to make any significant dent in the range of values allowed by the datatype so the best policy is not to worry about it.

If this is for some reason a real issue for you some possible workarounds are...

  1. You can use a SEQUENCE instead of an identity column and define a smaller cache size for example and use NEXT VALUE FOR in a column default.
  2. Or apply trace flag 272 which makes the IDENTITY allocation logged as in versions up to 2008 R2. This applies globally to all databases.
  3. Or, for recent versions, execute ALTER DATABASE SCOPED CONFIGURATION SET IDENTITY_CACHE = OFF to disable the identity caching for a specific database.

You should be aware none of these workarounds assure no gaps. This has never been guaranteed by IDENTITY as it would only be possible by serializing inserts to the table. If you need a gapless column you will need to use a different solution than either IDENTITY or SEQUENCE

Identity increment jumping in SQL Server

If I understood correctly then you are probably facing this issue Failover or Restart Results in Reseed of Identity. The reason is, when you allocate the IDENTITY values then a cache size of 1000 is allocated, so when you are restart the unused values are lost.

Identity column value suddenly jumps to 1001 in sql server

Microsoft has changed the way they deal with identity values in SQL Server 2012 and as a result of this you can see identity gaps between your records after rebooting your SQL server instance or your server machine. There might be some other reasons for this id gaps, it may be due to automatic server restart after installing an update.

You can use below two choices

  • Use trace flag 272
    o This will cause a log record to be generated for each generated identity value. The performance of identity generation may be impacted by turning on this trace flag.

  • Use a sequence generator with the NO CACHE setting

    Setting Trace Flag 272 on SQL Server 2012 that you are expecting here

  • Open "SQL Server Configuration Manager"

  • Click "SQL Server Services" on the left pane

  • Right-click on your SQL Server instance name on the right pane ->Default: SQL Server(MSSQLSERVER)

  • Click "Properties"

  • Click "Startup Parameters"

  • On the "specify a startup parameter" textbox type "-T272"

  • Click "Add"

  • Confirm the changes



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