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Sampling Problem with Filtered Statistics
published 711 days, 23 hours, 15 minutes ago posted by sasa 721 days, 17 hours, 36 minutes ago
Tuesday, February 23, 2010 4:45:21 AM GMT Saturday, February 13, 2010 10:24:53 AM GMT
Sampling Problem with Filtered Statistics
I was writing a blog post to show how to solve the problem of bad estimations due to uneven data distribution with filtered statistics. After an hour or so of banging my head against the wall, I discovered that I ran into a bug feature. It appears that if the predicate on the filtered stats [...] (more)
category: News | clicked: 0 | comment | | source: jasonmassie.com
tags: bugfix, filtered indexes, Query Optimizer, SQL Server, statistics
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Filtered Stats to Counter Data Skew Issues
published 715 days, 23 hours, 31 minutes ago posted by sasa 722 days, 2 hours, 6 minutes ago
Friday, February 19, 2010 4:29:33 AM GMT Saturday, February 13, 2010 1:55:10 AM GMT
Filtered Stats to Counter Data Skew Issues
There are a handful of things that can make SQL Server choose a “bad plan”. They usually revolve around variable sized result sets. Some problematic scenarios are parameter sniffing, data skew, local variables, table variables, UDF’s or complex calculations in the where clause. All of these and more are detailed in my favorite and recently [...] (more)
category: News | clicked: 2 | comment | | source: jasonmassie.com
tags: Query Optimizer, Query Tuning, SQL Server, statistics, TSQL
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Filtered Stats to Counter Data Skew Issues
published 834 days, 12 hours, 18 minutes ago posted by sasa 844 days, 54 minutes ago
Friday, October 23, 2009 3:42:26 PM GMT Wednesday, October 14, 2009 3:06:49 AM GMT
Filtered Stats to Counter Data Skew Issues
There are a handful of things that can make SQL Server choose a “bad plan”. They usually revolve around variable sized result sets. Some problematic scenarios are parameter sniffing, data skew, local variables, table variables, UDF’s or complex calculations in the where clause. All of these and more are detailed in my favorite and recently [...] (more)
category: News | clicked: 4 | comment | | source: jasonmassie.com
tags: Query Optimizer, Query Tuning, SQL Server, statistics, TSQL
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Sampling Problem with Filtered Statistics
published 835 days, 12 hours, 23 minutes ago posted by sasa 845 days, 1 hour, 32 minutes ago
Thursday, October 22, 2009 3:37:29 PM GMT Tuesday, October 13, 2009 2:28:15 AM GMT
Sampling Problem with Filtered Statistics
I was writing a blog post to show how to solve the problem of bad estimations due to uneven data distribution with filtered statistics. After an hour or so of banging my head against the wall, I discovered that I ran into a bug feature. It appears that if the predicate on the filtered stats [...] (more)
category: News | clicked: 1 | comment | | source: jasonmassie.com
tags: bugfix, filtered indexes, Query Optimizer, SQL Server, statistics
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Rebuilding Indexes vs. Updating Statistics
published 838 days, 12 hours, 38 minutes ago posted by sasa 848 days, 7 hours, 57 minutes ago
Monday, October 19, 2009 3:22:40 PM GMT Friday, October 09, 2009 8:03:20 PM GMT
Rebuilding Indexes vs. Updating Statistics
One of the questions I was asked recently while speaking at user groups, was regarding the order that jobs like rebuilding indexes or updating statistics should be performed as part of the database maintenance activities. Then I started writing this post about this topic on the weekend but was interrupted several times, including one of them to watch the premiere on VH1 of the movie Anvil: The Story of Anvil.   In general, the order should not matter, at least if you carefully consider these importan... (more)
category: Management | clicked: 2 | comment | | source: sqlblog.com
tags: Indexes, statistics
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SQL Server database design goals: Memory, Disk and I/O - maximize the scalability with monitoring
published 859 days, 14 hours, 3 minutes ago posted by sasa 862 days, 5 hours, 53 minutes ago
Monday, September 28, 2009 1:57:32 PM GMT Friday, September 25, 2009 10:07:43 PM GMT
SQL Server database design goals: Memory, Disk and I/O - maximize the scalability with monitoring
Do you consider the I/O whenever a database design project is assigned? It is one of the primary design goals of all database software is to minimize disk I/O because disk reads and writes are among the most resource-intensive operations. Over the time it may be one of the criteria that extensive usage of data and defautl behaviour on SQL Server builds a buffer pool in memory to hold pages read from the database. While queries are getting designed the code must be optimized and dedicated to minimizing...... (more)
category: News | clicked: 0 | comment | | source: sqlserver-qa.net
tags: capacity, disk, i/o, input, Memory, Monitoring, Performance, SQL Server, statistics, Tools
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How the Query Optimizer Uses Statistics – Part II
published 862 days, 14 hours, 14 minutes ago posted by sasa 872 days, 12 hours, 47 minutes ago
Friday, September 25, 2009 1:46:41 PM GMT Tuesday, September 15, 2009 3:13:45 PM GMT
How the Query Optimizer Uses Statistics – Part II
I got a question from a reader of my post How the Query Optimizer Uses Statistics (http://sqlblog.com/blogs/ben_nevarez/archive/2009/09/03/how-the-query-optimizer-uses-statistics.aspx) and I thought that it would be a good idea to post my answer here. Basically the request was to expand the previous example for a predicate with two columns.   First, a reminder that the histogram only shows the values of the first column of the statistics object. So, how the Query Optimizer does this?   One way to... (more)
category: Query | clicked: 1 | comment | | source: sqlblog.com
tags: Query Optimizer, statistics
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Statistics Used by the Query Optimizer in SQL Server White Paper
published 872 days, 14 hours, 59 minutes ago posted by sasa 879 days, 12 hours, 26 minutes ago
Tuesday, September 15, 2009 1:01:15 PM GMT Tuesday, September 08, 2009 3:34:50 PM GMT
Statistics Used by the Query Optimizer in SQL Server White Paper
In case you are not aware, the excellent white paper “Statistics Used by the Query Optimizer in SQL Server” has been updated for SQL Server 2008... (more)
category: News | clicked: 2 | comment | | source: sqlblog.com
tags: Query Optimizer, statistics
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How are auto-created column statistics names generated?
published 898 days, 10 hours, 47 minutes ago posted by sasa 904 days, 7 hours, 52 minutes ago
Thursday, August 20, 2009 5:13:29 PM GMT Friday, August 14, 2009 8:08:17 PM GMT
How are auto-created column statistics names generated?
This is a question that came up at the Cleveland SQL Server User Group last night. An attendee had a wager with his colleagues about how the names of auto-created column-level stats are generated... (more)
category: Query | clicked: 0 | comment | | source: www.sqlskills.com
tags: statistics
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Lies damned lies and statistics - Part II
published 901 days, 14 hours, 36 minutes ago posted by sasa 908 days, 12 hours, 7 minutes ago
Monday, August 17, 2009 1:25:13 PM GMT Monday, August 10, 2009 3:53:59 PM GMT
Lies damned lies and statistics - Part II
In previous post I listed situations where your statistics might need some special attention (http://sqlblog.com/blogs/elisabeth_redei/archive/2009/03/01/lies-damned-lies-and-statistics-part-i.aspx). As I mentioned in that post, the symptoms are typically related to more or less random variations in duration that cannot be explained by resource contention or blocking. A quick recap of the various problems you can encounter: 1. Statistics is out-of-date 2. T... (more)
category: Management | clicked: 1 | comment | | source: sqlblog.com
tags: Actual Rows, Estimated Rows, histogram, Skewed Data, statistics