DBCC Checkdb - Filling up tempdb log file - Wrong tempdb estimates

  • I have 3.5TB database( no partition, has multiple data files), estimates on this databases shows that DBCC Checkdb with all options should take about 452 MB of tempdb space ( 452 MB for CheckAlloc, 1 MB for Checktable) , after letting it run for 9 hours, i see that it has used more than 75GB space on tempdb data file and more than 200GB on log file for tempdb, is there a better way to get estimates on tempdb usage?

  • Known bug

    http://www.sqlskills.com/blogs/paul/how-does-dbcc-checkdb-with-estimateonly-work/

    Gail Shaw
    Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
    SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

    We walk in the dark places no others will enter
    We stand on the bridge and no one may pass
  • Makes sense. I did enabled traceflag 2562, now the estimated for CheckAlloc is 450MB and for CheckTable is 750GB !!!. Looks like enabling trace flag 2562 and getting estimates is the way to go. Does the estimate including data and log file usage for tempdb?

  • Not sure, but I suspect it'd be data file usage.

    Gail Shaw
    Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
    SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

    We walk in the dark places no others will enter
    We stand on the bridge and no one may pass

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