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Category: Error Handling

Error Handling With Extended Events, Part 2

Published 2016-09-19 by Kevin Feasel

Dave Mason continues his discussion of using Extended Events to handle errors:

In the last post, we explored a couple of examples of using Extended Events to enhance T-SQL error handling. There was some potential there. But a hard-coded SPID was necessary: we couldn’t use the code examples for anything automated. It was cumbersome, too. Let’s change that, shall we?

To make the code easier to work with, I moved most of it into three stored procs: one each to create an XEvent session, get the XEvent session data, and drop the XEvent session. There’s also a table type. This will negate the need to declare a temp table over and over. The four objects can be created in any database you choose. I opted to create them in [tempdb]. The code for each is below in the four tabs.

This is a very interesting solution.

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Error Handling Extended Event

Published 2016-09-15 by Kevin Feasel

Dave Mason shows how to use an Extended Event to capture error data:

Here’s an example for DBCC CHECKDB on a corrupt database. Remember from the last post that in this scenario, control never passes to the CATCH block. So we’ll need to check the Event Session data after END CATCH. You can also run this as a single batch in SSMS, but you’ll need a corrupt database to get similar results. As before, replace “2016” with your SPID.

There are a lot of working parts to this, so read the scripts carefully if you’re interested in implementing something similar yourself.

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Troubleshooting Event Hub Issues

Published 2016-09-12 by Kevin Feasel

Ginger Grant walks through a couple of issues you might run into with Event Hub:

The input for this stream is set to an event hub which has a standard subscription. The basic subscription, which is of course cheaper, has one default consumer group. With a standard subscription multiple consumer groups can be created and more importantly named. When setting up the inputs there is a blank for the name of the consumer group. If you have a basic subscription this will be empty. If it is empty, then the event hub won’t pass data to the stream analytics job. Perhaps there is a way to get a basic event hub to work with a stream analytics job, but I couldn’t make it happen. When I created an event hub with a standard subscription and created a consumer group and added that name to the input of a streaming analytics job, it worked.

Read on for details.

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Powershell Failing On Error

Published 2016-09-12 by Kevin Feasel

Michael Bourgon has a helpful tip for those CmdExec SQL Agent jobs which run Powershell scripts which won’t fail on error:

However, when run via SQL Agent, it succeeds.  GAH!
I tried 50 different variations; modifying the script, various TRY..CATCH blocks found on the internet.  Nothing.  Every single one of them succeeded.

Then I remembered that by default, even though it had an error, by default errors always continue.  ($ErrorActionPreference=”Continue”.  So I added this line at the top:

Read on for the answer.

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Try-Catch Blocks

Published 2016-09-08 by Kevin Feasel

Dave Mason discusses a major problem with try-catch blocks:

We didn’t just lose one error. We lost them all! DBCC CHECKDB on a corrupt database just came back “clean” and the CATCH block never executed. We’ve moved into dangerous territory now. This is no longer an inconvenience or an annoyance. This could lead to data loss, financial harm to your company, maybe even some risk to your career.

Dave promises a better approach in his next post.

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Troubleshooting Data Factory Errors

Published 2016-08-29 by Kevin Feasel

Ginger Grant discusses Azure Data Factory errors:

Unfortunately, while developing Data Factory I became very familiar with errors. All of the errors show up at the end and provide very little insight as to what in the process failed. Here’s an example.

Database operation failed on server ‘Sink:DBName01.database.windows.net’ with SQL Error Number ‘40197’. Error message from database execution : The service has encountered an error processing your request. Please try again. Error code 4815. A severe error occurred on the current command. The results, if any, should be discarded.

This sounds like classic Microsoft error messages:  “An error occurred.  Here is a code you can put into Google and hope desperately that someone has already figured out the answer.  Good luck!”

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Error Severity Levels Greater Than 18

Published 2016-07-26 by Kevin Feasel

Manoj Pandey was debugging an Informatica ETL and got back an uncommon error message:

So, to identify the cause I tried to execute the above MERGE statement directly and I got the same error:

EXEC spMergeTables 'STG.ABCtblXYZ','ABC.tblXYZ'

(0 row(s) affected)
Msg 2754, Level 16, State 1, Procedure spMergeTables, Line 107
Error severity levels greater than 18 can only be specified by members of the sysadmin role, using the WITH LOG option.

This is a case in which an immediate error obscured the actual error.

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SET XACT_ABORT On By Default

Published 2016-07-06 by Kevin Feasel

Tibor Karaszi notes an important change to SQL Server Management Studio with the July 2016 release:

Now, exposing one more SET option can’t be bad, right? But Erland Sommarskog found out that this is checked by default. Now, using XACT_ABORT might now [sic] be a bad thing, au contraire. See this one of Erland’s series of error handle articles.

Making this change after all of these years is a little odd.  Making it in a regular update is very odd.  Using SET XACT_ABORT ON is a smart move in general, but there are times in which you don’t want to rollback immediately after an error; the problem is, are all of those places in your code well-documented?

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Try-Catch Doesn’t Handle Everything

Published 2016-05-19 by Kevin Feasel

Tara Kizer notes that there are limits in what TRY/CATCH blocks handle in SQL Server:

It’s well documented in Books Online (BOL). If you’re like me, then tl;dr. Are we even calling it Books Online these days? I still say “bookmark lookup” instead of “key lookup”. I suppose I’ll be saying Books Online for quite some time too. At least these days it really is online.

Here’s a shortened version:

  • Warnings or informational messages that have a severity of 10 or lower

  • Errors that have a severity of 20 or higher that stop the session

  • Attentions

  • When a session is KILLed

It’s important to know that not everything gets caught, particularly major issues.

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Watch Named, Nested Transactions

Published 2015-12-17 by Kevin Feasel

Gail Shaw finishes her outstanding series on transactions:

The error was thrown by the ROLLBACK statement. As such, the transaction is still open, the locks are held and the transaction log space can’t be reused. Unless the application that called this was checking for open transactions, that transaction could potentially be left open for quite some amount of time, causing blocking and/or the transaction log to grow.

It’s not just that someone in the future might call the code from another stored proc within a transaction, it’s also that it might be that the code is called from an application which started a transaction. Or called from SSIS which started a transaction. It’s very hard to ensure that code is never called from within an existing transaction

Read the whole thing.

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