[MonetDB-users] selection queries
Hi,
I was trying out selection queries with varying selectivity factors on a 1 million tuple relation. The selectivity factors for predicates were 0.1%, 1% and 10% of the entries in the column and the data type of the column is int. What I'm seeing is that the execution time increases with selectivity factors going from 0.1% to 1% to 10%. I'm not sure why this is happening though, considering its a column-store system. Should this be attributed to increase in CPU time or disk I/Os or any other factor? What my understanding of column-store systems is that the execution time should remain constant for varying selectivity factors for the same column. Any help would be appreciated.
Thanks
Mayank
Mayank Maheshwari mayank@cs.wisc.edu
Mayank Maheshwari wrote:
Hi,
I was trying out selection queries with varying selectivity factors on a 1 million tuple relation. The selectivity factors for predicates were 0.1%, 1% and 10% of the entries in the column and the data type of the column is int. What I'm seeing is that the execution time increases with selectivity factors going from 0.1% to 1% to 10%. I'm not sure why this is happening though, considering its a column-store
well, intermediate results are created, which explains the time increase.
system. Should this be attributed to increase in CPU time or disk I/Os or any other factor? What my understanding of column-store systems is that the execution time should remain constant for varying selectivity factors for the same column. Any help would be appreciated.
no, it remains constant only if there is no result table produced. Be aware that MonetDB always materializes the intermediat results.
Thanks
Mayank
Mayank Maheshwari mayank@cs.wisc.edu
The NEW KODAK i700 Series Scanners deliver under ANY circumstances! Your production scanning environment may not be a perfect world - but thanks to Kodak, there's a perfect scanner to get the job done! With the NEW KODAK i700 Series Scanner you'll get full speed at 300 dpi even with all image processing features enabled. http://p.sf.net/sfu/kodak-com _______________________________________________ MonetDB-users mailing list MonetDB-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/monetdb-users
On Tue, May 12, 2009 at 06:19:49PM -0500, Mayank Maheshwari wrote:
Hi,
I was trying out selection queries with varying selectivity factors on a 1 million tuple relation. The selectivity factors for predicates were 0.1%, 1% and 10% of the entries in the column and the data type of the column is int. What I'm seeing is that the execution time increases with selectivity factors going from 0.1% to 1% to 10%. I'm not sure why this is happening though, considering its a column-store system. Should this be attributed to increase in CPU time or disk I/Os or any other factor? What my understanding of column-store systems is that the execution time should remain constant for varying selectivity factors for the same column. Any help would be appreciated.
Range selections on non-sorted data are linear in both the input size, the result length (selectivity) and the result width (projectivity).
Stefan
Thanks
Mayank
Mayank Maheshwari mayank@cs.wisc.edu
The NEW KODAK i700 Series Scanners deliver under ANY circumstances! Your production scanning environment may not be a perfect world - but thanks to Kodak, there's a perfect scanner to get the job done! With the NEW KODAK i700 Series Scanner you'll get full speed at 300 dpi even with all image processing features enabled. http://p.sf.net/sfu/kodak-com _______________________________________________ MonetDB-users mailing list MonetDB-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/monetdb-users
participants (3)
-
Martin Kersten -
Mayank Maheshwari -
Stefan Manegold