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  • re: SAN Configuration Performance Problems

    Time to market is extremely important. I hope DBA, or rather the data architect does not become a severe impediment. I would rather people put together a SQL Server db quickly, and correct over time. As I understand it, LinkedIn was slapped together. As they grew, it became apparent that any change would break many things, so they took time to fix ...
    Posted to Joe Chang (Weblog) by jchang on March 3, 2015
  • SAN Configuration Performance Problems

    The charts provided here illustrates my complaints against SAN vendor doctrine, obstinately adhering to the concept of one large pool of disks from which all volumes are created for any purpose (data, log, and junk). There is no consideration for the radically different characteristics of hard disks in random versus sequential IO (low and ...
    Posted to Joe Chang (Weblog) by jchang on March 2, 2015
  • re: ExecStats update - automating execution plan analysis

    build now has legend font size 8, settable in the config file
    Posted to Joe Chang (Weblog) by jchang on February 18, 2015
  • ExecStats update - automating execution plan analysis

    It has been over 7 years now that I have made my ExecStats (current version Exec Stats 2015-02-18) tool publicly available (late 2007), with prototype versions going back to 2006. The two distinguishing elements of ExecStats is 1) the emphasis on cross-referencing a) query execution statistics to b) index usage via the c) execution ...
    Posted to Joe Chang (Weblog) by jchang on February 16, 2015
  • re: Geek City: Creating New Tools for Statistics

    its too bad we cannot create system views, I think this would be helpful as a view that could be worked into other queries. I put out a partial decode of stats_stream at It would be nice if MS made the stats_stream binary available via a dmv/f instead of DBCC. We could make a function, and have the ...
    Posted to Kalen Delaney (Weblog) by jchang on February 16, 2015
  • extensions for sp_helpindex

    The system stored procedures in SQL Server from the very beginning(?) provide useful information. However they have not been updated in a substantial manner for the new features in later versions, nor have they been extended with additional details that are now available in the DMVs for more sophisticated DBA's. Presumably, this is for ...
    Posted to Joe Chang (Weblog) by jchang on October 6, 2014
  • re: Join Row Estimation in Query Optimization

    great investigation. it looks like CE is doing what I described above. presumably this would not be invoked unless the plan cost was high, and perhaps also if it is known that the column in the next table was heavily skewed, making the effort worth while. If there is an index on the SARG column of the first table, followed by the join column, then ...
    Posted to Joe Chang (Weblog) by jchang on July 8, 2014
  • re: Join Row Estimation in Query Optimization

    temp tables can be particularly troublesome. I have seen the optimized assumed that the join to a temp table column was many-to-many, example 1000 rows in the temp table, expected to match to 1:1 or 1:few, but the optimizer assumed each row from temp mapped to 1000 in the permanent. Sometime just creating an index you don't need, but it fixed ...
    Posted to Joe Chang (Weblog) by jchang on July 7, 2014
  • Join Row Estimation in Query Optimization

    This topic is titled to specifically consider only row estimation after joins, precluding discussion of row estimates at the source table, which has already been addressed in papers covering the new Cardinality Estimator in SQL Server 2014 and other statistics papers for previous versions of SQL Server. There are certain situations in which ...
    Posted to Joe Chang (Weblog) by jchang on July 7, 2014
  • re: TPC-H and Columnstore Update

    note to companies publishing TPC-H results on SQL Server. It might be wise to take up TK's offer. It would be hard to find better quality advise. I would be interested too. It would be even helpful if you provided the actual sqlplan files, if not generally, then just to us.
    Posted to Joe Chang (Weblog) by jchang on July 7, 2014
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