Monday, June 28, 2010

Report Server issues

I’ve had a lot of Report Server issues in the last few months. I thought we solved it once, only to see it come up again in a slightly different way. But I think I can put it all to bed now.

The first time was a few months ago, right when I left on vacation (isn’t that always the way?). The C drive on one of our reporting servers began to run out of space, filling up 6 – 8 GB in a matter of hours.

Before I get too far ahead of myself, let me describe our layout. We have four regional databases running SQL 2005 Standard Edition, each with data for that region. Two regions are in our corporate headquarters, the other two are in my office. We also have two SQL 2008 Standard Edition servers that run in a virtual environment, one in each datacenter. The reports hosted on each reporting center are identical except for their data sources; the corporate report server fetches data from the two corporate databases, and the local server does the same. The issue we had was on the server in the corporate datacenter.

Our first step was to check the temp files. We noticed a few small files and one massive, 8 GB file that we couldn’t delete without stopping and restarting the report service. A few hours later the massive file reappeared. All of these temp files were prefixed “RSTemp_”.

We moved the location of the temp files to a larger drive to give us more time before the largest temp file grew too large. By default the location is on C:\Program Files\Microsoft SQL Server\MSRS10.<<Instance Name>>\Reporting Services. You can change it by modifying the rsreportserver.config file and adding the entry to the <Service> tag:



That gave us extra space, but it didn’t solve the issue. A little more digging showed that we had a long running report that was also getting bad data. The query for the report was looking for a scalar value but was returning multiples. The query was also a long running query. What we found was happening was that the report execution was timing out, but the query was still active. The user didn’t see the timeout and constantly tried to re-run the report. Consequently this report was continuously paged out to disk, and it never died. Once we cleaned up the data and fixed the reports query, the problem hasn’t reappeared.

The next issue was related to performance. We noticed at certain times of day the report server would get really sluggish. Reports that would complete in 10 seconds would now take 10 minutes. Looking at the server resources showed no increase in CPU, IO, or memory usage. We didn’t see a repeat of the super-big temp file, though there was an increase in the number of temp files.

A little more investigation showed that, when the performance began to degrade, there were locks being held by one process clearing the sessions that blocked another process that was writing session data. We were finally able to track this to a third party application we use to monitor performance. It didn’t look like the software was configured properly.

In investigating both of these issues we looked at the data in the ExecutionLogStorage table in the ReportServer database. If you’re not familiar with this table, you should check out Robert Bruckner’s excellent post on ExecutionLog2 View - Analyzing and Optimizing Reports.

In the first issue, we were able to identify the report by seeing the pagination values in the additional information data. In the second, we could spot when the slowness would begin by seeing the TimeProcessing values rise.         

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