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Are there less used indexes on the database?
However, it’s not so simple as it appears: These may be the less used indexes on the database, but when the most used ones have numbers like 100.000 seeks, it will not be difficult to find the less used ones with numbers such as 10.000 .
Are there any good tips for query optimization?
There are many literature and internet publications on techniques and best practices of query optimization, covering all available database management systems, like Oracle and MySQL. But I decided to share my own experience in the field with the focus on SQL Server query optimization tips.
Why do I need to look for drop indexes?
The reason you are looking for drop indexes is because your environment is on premises, you are running short on disk space and you just discovered you have some indexes which are many times the size of the table and is trying to discover if they are really useful.
Why is this query not using my nonclustered index?
The first query uses the clustered index, the second query uses my non-clustered index. My question is two parts: Why, since both queries have a WHERE clause on the [DateEntered] field, does the server use the clustered index on the first, but not the second?
What to do if SQL refuses to use the index?
If this simple SQL refuses to use the index, then there is a fundamental problem. Get the DBA to drop and rebuild the index. If the sample SQL above doesuse the index, then start with your original SQL and remove lines one at a time, running each successively smaller SQL through Explain Planas you go.
Why is the index not being used in Oracle?
Run your SQL through Explain Planand confirmed that the desired index is not being used. Checked the statisticson the underlying table. Confirmed that the index exists. Oracle will ignore an index for a number of reasons, but they boil down to two possibilities:
What to do when an index is not used?
The solution for this problem is the use of XQUERY extension functions, which allow the access to external items, such as collumns and variables, from the XQUERY expression. Using these extensions we can make the string concatenation in a custom field and make a reference to it.
When is the index not being used in XML?
However, analysing the query plan XML you will discover the index is most being used for updates, meaning the index is being updated when a record is updated. The plans where the index is being used for update are not needed for us on this query, they are exactly what create problems for performance.
What does it mean when an index is not being used?
It means the index tree is being used to go directly to the records we need. Index Scan: Not so good as an index seek, so it could be better. However, sometimes even an index scan is good, a non clustered index scan means the pages of that index are smaller an better for a scan than the pages of the clustered index.
Which is the best use of an index?
First, some basic definitions, without going into many details: Index Seek: That’s the best and desirable use of the index. It means the index tree is being used to go directly to the records we need. Index Scan: Not so good as an index seek, so it could be better.