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  • 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
  • re: TPC-H and Columnstore Update

    by my calculation, a 3X improvement in one of the 22 TPC-H queries (plus 2 refresh statements) contributes a 4.7% improvement in the Power test X^(1/24) If two queries can be improved by 3X each (Q10 and Q4) then that's a 9.6% gain on Power.
    Posted to Joe Chang (Weblog) by jchang on July 6, 2014
  • TPC-H and Columnstore (Update)

    Earlier I had commented on the TPC-H results published in April of this year for SQL Server 2014 using clustered column store storage, noting that two of the 22 TPC-H queries did not perform well in column store. I had speculated on the reason without investigation (I should have learned by now not to do this), that perhaps the cause ...
    Posted to Joe Chang (Weblog) by jchang on July 5, 2014
  • re: TPC-H Benchmarks on SQL Server 2014 with Columnstore

    On the tpch_interim link in the section TPC-H SF 100 Execution Plans you have to save target as. the links have the *.html extension but are actually sqlplan files for example note the name tpch_sf100_nonparallel_nc.sqlplan.html so save this as tpch_sf100_nonparallel_nc.sqlplan
    Posted to Joe Chang (Weblog) by jchang on June 9, 2014
  • TPC-H Benchmarks on SQL Server 2014 with Columnstore

    Three TPC-H benchmark results were published in April of this year at SQL Server 2014 launch, where the new updateable columnstore feature was used. SQL Server 2012 had non-updateable columnstore that required the base table to exist in rowstore form. This was not used in the one published TPC-H benchmark result on SQL Server 2012, which ...
    Posted to Joe Chang (Weblog) by jchang on June 9, 2014
  • re: Geek City: A Hint of Degrees

    I would not recommend setting sys.configures max degree of parallelism to 1 even if certain queries are set specifically to a higher value. I do agree with setting the system wide value low, but &gt; 1. It is not appreciated that certain query plans are actually more CPU efficient at DOP &gt; 1. Not just run faster with lower elapsed time, but ...
    Posted to Kalen Delaney (Weblog) by jchang on June 4, 2014
  • re: Detecting Hyper-Threading state

    Let me reiterate that: yes this information is available in WMI, but exposing it via DMV is better, especially since the SQL Server knows it. for now, try appropriate variations of the this: EXEC sys.xp_readerrorlog 0, 1, &quot;detected&quot;, &quot;socket&quot;
    Posted to Joe Chang (Weblog) by jchang on May 28, 2014
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