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SQL I/O Latency and Disk Issue – The missing link
Say for example the application has been written with performance in mind, all queries are optimal, no index issues, databases are fully optimized through a nightly job or manually, and the best I/O...
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Covering Index – A “Adam and Eve” Style
We know that in SQL Server there is a limitation on index key which is 900 bytes. This means that the total length of an index must not exceed 900 bytes. Until SQL 2000, we used to create a covering...
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TCP Chimney Offloads and SQL Server Implementation
A lot of us often see the following type of sporadic messages although everything is running as usual. After the application or user receives the network related messages, there will be some trouble...
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DBCC CHECKDB – “After death comes the doctor”
It is a common practice for a lot of us to run DBCC CHECKDB before backing up the database. Doing so on a small database performance impact may be negligible. However, for a large and high-end OLTP...
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SQL Server 2012 AlwaysON: "Automatic Page Repair" - how does it work?
SQL Server 2012 brought us a new HADR (high availability disaster recovery) feature and declares that database mirroring will be deprecated in future versions. Like database mirroring, AlwaysON has a...
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Non-clustered indexes per table – how many indexes are too many?
There is a strong recommendation that “Don’t create too many indexes, because it degrades performance due to overhead of DML operations”. Having indexes on a table is necessary and on the other hand it...
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System database issues: rebuild, relocation and restore - Are we ready?
"What is the probability that the sun will NOT rise tomorrow?"“What is the probability that the master database will NOT corrupt tomorrow?” To answer the first question, we have to live billions of...
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Missing Index DMVs – misleading suggestions
Creating missing indexes is one of DBA’s core responsibilities in the production environment and makes the query execution much faster. A lot of enhancement has been done and new features have been...
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Network Binding Order – SQL 2012 Failover Cluster Installation
“The domain network is not the first bound network. This will cause domain operations to run slowly and can cause timeouts that result in failures. Use the Windows network advanced configuration to...
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“ANSI_NULLS”, “JOIN/WHERE” and “Query Optimizer” - story of the three stooges
A friend of mine who lives in Nova Scotia is managing a couple of large busy OLTP database servers. A few days ago, he asked me curiously, what’s going on with “ANSI_NULLS” here. Although, the...
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Realtime SQL Server Performance Monitoring - A simple way to see SQL Server...
Background of the tool:“SQL Performance Monitor”. It is completely Free, Agent less, No Installation/Configuration is required, Single executable and portable, easy to use and only needs a couple of...
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WRITELOG waittype - Implicit vs. Explicit Transaction: disk or coding issue?
In a OLTP system where concurrency is high observing WRITELOG waittype is normal for a short period of time during peak usage. Generally, a high value of this waittype indicates slow response of the...
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MAXDOP - What triggers Parallelism?
Charles Darwin was an English naturalist. He established that all species of life have descended over time from common ancestors and proposed the scientific theory that this branching pattern of...
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Performance issues from ORDER BY/GROUP BY - spills in tempdb
It is very common and expected to see a query containing ORDER BY or GROUP BY clause for displaying or grouping purposes. It is also common that developers use ORDER BY clause from a habit without...
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Execution Plan and “SQL Sentry Plan Explorer” – it's like a hand of god!
There are numerous articles that have been written on how out-dated statistics cause severe performance issues. I am hesitant to add one more to that long list. However, this time I’ll be using “SQL...
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SQL Server Port - How to open in Windows Firewall
In the IT security world, it is said that approximately 80% of all security breaches occur by insiders; directly or indirectly, willingly or unwillingly. Here our focus is local Windows firewall and to...
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Self-join incurs more I/O activities and increases locking overhead!
The Self-Join technique is commonly used to create a hierarchical tree set or finding duplicate records. It is also used to find previous or next values from a table by utilizing the inline table...
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Index optimization - REBUILD vs. REORGANIZE
Index optimization is probably one of the most critical task every database support personnel has to perform on a regular basis. Based on DML operations in a particular environment, we adopt various...
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Secret of "sp_updatestats"– feed your dragon
Query Optimizer vs. HR ManagerLet’s say you’re working in a company where there’s a couple of departments. Each department has a certain number of employees.feed your dragon every dayThe HR manager...
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Expected or Unexpected data file growth – how to manage?
As the business is growing, the database needs to grow at the same time. It is common to pre-size the data file beforehand based on various recorded activities. Usually the DBA manually increases the...
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