SSMS: Database Consistency History Report

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In real life, Database consistency check is one of the critical operations a DBA generally doesn’t give much priority. Many readers of my blogs have asked many times, how do we know if the database is consistent? How do I read output of DBCC CHECKDB and find if everything is right or not?

My common answer to all of them is – look at the bottom of checkdb (or checktable) output and look for below line.

CHECKDB found 0 allocation errors and 0 consistency errors in database ‘DatabaseName’.

Above is a “good sign” because we are seeing zero allocation and zero consistency error. If you are seeing non-zero errors then there is some problem with the database. Sample output is shown as below:

CHECKDB found 0 allocation errors and 2 consistency errors in database ‘DatabaseName’.repair_allow_data_loss is the minimum repair level for the errors found by DBCC CHECKDB (DatabaseName).

If we see non-zero error then most of the time (not always) we get repair options depending on the level of corruption. There is risk involved with above option (repair_allow_data_loss), that is – we would lose the data. Sometimes the option would be repair_rebuild which is little safer. Though these options are available, it is important to find the root cause to the problem.

In standard report, there is a report which can show the history of checkdb executed for the selected database. Since this is a database level report, we need to right click on database, click Reports, click Standard Reports and then choose “Database Consistency History” report.

The information in this report is picked from default trace. If default trace is disabled or there is no checkdb run or information is not there in default trace (because it’s rolled over), we would get report like below.

As we can see report says it very clearly: Currently, no execution history of CHECKDB is available or default trace is not enabled.

To demonstrate, I have caused corruption in one of the database and did below steps.

1. Run CheckDB so that errors are reported.
2. Fix the corruption by losing the data using repair option
3. Run CheckDB again to check if corruption is cleared.

After that I have launched the report and below is what we would see.

If you are lazy like me and don’t want to run the report manually for each database then below query would be handy to provide same report for all database. This query is runs behind the scenes by the report. All I have done is remove the filter for database name (at the last – highlighted).

DECLARE @curr_tracefilename VARCHAR(500);DECLARE @base_tracefilename VARCHAR(500);DECLARE @indx INT;
SELECT @curr_tracefilename = path FROM sys.traces WHERE is_default = 1;
SET @curr_tracefilename = REVERSE(@curr_tracefilename);SELECT @indx  = PATINDEX('%\%', @curr_tracefilename) ;SET @curr_tracefilename = REVERSE(@curr_tracefilename);SET @base_tracefilename = LEFT( @curr_tracefilename,LEN(@curr_tracefilename) - @indx) + '\log.trc';
SELECT  SUBSTRING(CONVERT(NVARCHAR(MAX),TEXTData),36, PATINDEX('%executed%',TEXTData)-36) AS command
,       LoginName
,       StartTime
,       CONVERT(INT,SUBSTRING(CONVERT(NVARCHAR(MAX),TEXTData),PATINDEX('%found%',TEXTData)+6,PATINDEX('%errors %',TEXTData)-PATINDEX('%found%',TEXTData)-6)) AS errors
,       CONVERT(INT,SUBSTRING(CONVERT(NVARCHAR(MAX),TEXTData),PATINDEX('%repaired%',TEXTData)+9,PATINDEX('%errors.%',TEXTData)-PATINDEX('%repaired%',TEXTData)-9)) repaired
,       SUBSTRING(CONVERT(NVARCHAR(MAX),TEXTData),PATINDEX('%time:%',TEXTData)+6,PATINDEX('%hours%',TEXTData)-PATINDEX('%time:%',TEXTData)-6)+':'+SUBSTRING(CONVERT(NVARCHAR(MAX),TEXTData),PATINDEX('%hours%',TEXTData)+6,PATINDEX('%minutes%',TEXTData)-PATINDEX('%hours%',TEXTData)-6)+':'+SUBSTRING(CONVERT(NVARCHAR(MAX),TEXTData),PATINDEX('%minutes%',TEXTData)+8,PATINDEX('%seconds.%',TEXTData)-PATINDEX('%minutes%',TEXTData)-8) AS time
FROM::fn_trace_gettable( @base_tracefilename, DEFAULT)
WHERE EventClass = 22 AND SUBSTRING(TEXTData,36,12) = 'DBCC CHECKDB'-- AND DatabaseName = @DatabaseName;

Don’t get worried about the logic above. All it is doing is reading the trace files, parsing below entry and getting out information for underlined words.

DBCC CHECKDB (CorruptedDatabase) executed by sa found 2 errors and repaired 0 errors. Elapsed time: 0 hours 0 minutes 0 seconds.  Internal database snapshot has split point LSN = 00000029:00000030:0001 and first LSN = 00000029:00000020:0001.

Hopefully now onwards you would run checkdb and understand the importance of it. As responsible DBAs I am sure you are already doing it, let me know how often do you actually run them on you production environment?