SQL Server 2008 error handling best practice

  • Article

Error handling in SQL Server 2008 needs careful implementation. The Microsoft “Oslo” Repository’s API has the further problem that we cannot mandate the error handling logic in our callers. Thus a stored procedure call could be in a transaction or not and in a try-catch block or not. Below is the pattern we have chosen based on experimentation and best practice guidance from the SQL Server team and other SQL Server experts. A test script for all the interesting cases can be found at https://blogs.msdn.com/cfs-file.ashx/__key/communityserver-components-postattachments/00-09-46-95-77/Error-Handling.sql.

For a good overview of SQL Server error handling see https://www.sommarskog.se/error-handling-I.html and https://www.sommarskog.se/error-handling-II.html. In our design, we had the following main issues and mitigations:

·         A transaction rollback will rollback to the outermost transaction but if there is an outer transaction we would like to only rollback the changes to the module’s inner transaction. The solution is to use SQL Server save points if there is an outer transaction.

·         A sufficiently severe raiserror will terminate a module if there is an outer try-catch block but if there is none then execution will continue in the module. The solution is to always explicitly return after raising an error.

·         Some developers like to use stored procedure return values to encode error states. The solution is to return appropriate error codes.

·         SQL Server will raise warnings if the transaction depth entering and leaving a transaction do not match. The solution is to be careful.

·         Triggers have an implicit transaction. The solution is to use a simplified pattern for triggers where a transaction is never started.

·         Save points need unique names if modules can nest otherwise you can rollback to the wrong save point. The solution is to use a GUID to name the save points.

Here is the pattern for stored procedures (eliding our special error reporting routines):

ifparameter error
begin
raiserror(N'…', 16, 0);

return -1;
end
else
begin
begin try
declare @hasOuterTransaction bit = case when @@trancount > 0 then 1 else 0 end;
declare @rollbackPoint nchar(32) = replace(convert(nchar(36), newid()), N'-', N'');

if @hasOuterTransaction = 1
begin
save transaction @rollbackPoint;
end
else
begin
begin transaction @rollbackPoint;
end;

Do work;

if @hasOuterTransaction = 0
begin
commit transaction;
end;
end try
begin catch
if xact_state() = 1
begin
rollback transaction @rollbackPoint;
end;

execute Standard module error handler;

    return -error_number();
end catch;
end;

Here is the pattern for triggers (eliding our special error reporting routines):

ifparameter error
begin

  rollback transaction;

  raiserror(N'…', 16, 0);

 

  return;
end
else
begin
begin try

Do work;

  end try
begin catch
rollback transaction;

execute Standard module error handler;

    return;
end catch;
end;

 

 

Error Handling.sql

Comments

  • Anonymous
    March 10, 2009
    PingBack from http://www.anith.com/?p=17268
  • Anonymous
    August 03, 2009
    The comment has been removed
  • Anonymous
    September 03, 2009
    For stored procedues, in the catch block, it is not currently handling the case where there is no outer transaction and the transaction state is uncommitable.Should the catch block be as below?-- an error occurred, we must rollback only the work done in this sprocIF @hasOuterTransaction = 0BEGIN
    -- we started the transaction, so rollback the complete transactionROLLBACK TRANSACTION
    ENDELSEBEGIN
    -- there is an outer transaction, do not rollback changes before this sproc was calledIF XACT_STATE() <> -1BEGIN    -- the transaction is still valid, just rollback to the save point    ROLLBACK TRANSACTION @rollbackPointEND-- else that means the transaction is uncommitable, just let the caller rollback the transaction
    END-- error handling...
  • Anonymous
    October 02, 2009
    Great stuff, Anthony.  I really like your recommendations.-KevinTwitter @kekline
  • Anonymous
    February 19, 2010
    No way that the save transaction  @rollbackPoint; in the template you submit is to be used: case is when a calling procedure remotely calls another one. You'll catch an error as save transaction is not supported in remote calls (Too bad!!!!).BOL: [SAVE TRANSACTION is not supported in distributed transactions started either explicitly with BEGIN DISTRIBUTED TRANSACTION or escalated from a local transaction.]I had the issue and had to completely review all my template.Hope this will help
  • Anonymous
    July 03, 2010
    what this error means:Incorrect syntax near 'AF14C8CF'the floating point value '28E218132931' is out of the range of computer representation (8 bytes). Unclosed quotation mark after the character string 'order by datname'
  • Anonymous
    September 12, 2010
    Has anyone addressed the issue with distributed transactions/remotely executed calls (noted by "PR")?I have few instances where this applies, however it is prudent, as we are discussing 'pattern' and not just implementation.Thanks!
  • Anonymous
    February 23, 2011
    I like the this error handling pattern but it has issue to deal with doomed transaction.
  • Anonymous
    August 26, 2012
    hi is there a way to do a try catch block that does all or none procedures something like this.tryproc1proc2proc3catchrollbackendtryi mean to do all or do none?thank you