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Foglight for SQL Azure 5.5.8.6 - User Guide

Introducing Foglight for SQL Azure Adding and Configuring Agents Reviewing SQL Azure Activity Reviewing Database Usage Reviewing the Database Properties Monitoring Estimated Costs Viewing User Metrics Using the Global Administration Options Reviewing Foglight for SQL Azure Alarms Glossary

Indexes table

The Indexes table shows the index statistics for all indexes in the selected tables.
SQL Azure stores statistics about the distribution of the key values in each index, and uses these statistics to determine which indexes to use in query processing.
Clicking a single row in the Indexes table displays a popup with detailed index statistics for that index.
 
* 
IMPORTANT: To create a custom filter for the Indexes table, use the options accessible by clicking the Customizer button at the table’s upper right side. For details, see Components Shared by all Foglight for SQL Azure Screens on page 13.
The columns displayed in the Indexes table are as follows:
 
Table 2.  
Column
Description
Database Name
The name of the specified database.
Owner
The owner of the index.
Table
The table with which the index is associated.
Index Name
The name of the index.
Index Type
The type of the index:
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Clustered—the default index type, whose creation is mandatory when creating a table in SQL Azure
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Non-clustered
Total Reserved Size
The total amount of space reserved for the index, in megabytes.
Total Used Size
The total amount of space used by the index, in megabytes.
Total Free Size
The total amount of unused space in the index, in megabytes.
Percent of DB
The percentage of space the selected index occupies within the entire database.
Is Disabled
Indicates whether the index is disabled.
Is Hypothetical
Indicates whether the index is hypothetical.
Fill Factor
The fill factor used when creating an index, in order to reserve a percentage of free space on each data (leaf level) page.
Is Padded
Indicates whether to use the fill factor also for the index intermediate pages.
Has Filter
Indicates whether the index is covering only filtered data.
Index Cost Weight
The percentage the table occupies from the database size (Including the free space).
Is Unique
Indicates whether the index is unique.
Is Primary Key
Indicates whether the index is a primary key.
Figure 1. Clicking a single index in the Indexes table displays the Index Properties popup.
The Index Properties popup
The Index Properties popup contains the components described in the following sections:
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Index Details on page 43
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Index Density table on page 44
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Index Histogram table on page 44

Index Details

The Index Details section provides the following data about the index:
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Last updated statistics—the time and date that the statistics were last updated.
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Rows—the number of rows in the index.
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Rows sampled—the number of rows sampled for statistics information.
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Steps—the number of distribution steps.
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Density—the density value (percent) of the index; see definition of Density in the Index Density table.
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Avg key length—the average length of all of the index columns.

Index Density table

The Index Density table shows the density values for each combination of columns in the index.
The Index Density table contains the following columns:
 
Table 3.  
Statistic
Description
Columns
The name of the columns in the index.
Density
The density value (percent) of the index, namely: the index’s degree of selectivity, which affects the efficiency of searches in the index; the more selective an index is, the more useful it is in searches. Density is calculated as 1 / distinct values for all values in the first key column of the statistics object, excluding the histogram boundary values.
Average Key Length
The average length (number of bytes) of all of the index’s key columns.

Index Histogram table

When a single index is selected in the Indexes table, the Index Histogram table displays the index distribution histogram for the selected index.
When SQL Azure collects statistics on an index, for use in determining the indexes usefulness for resolving queries, it samples the data in the index and produces a histogram of the key values found. This table shows that histogram for the selected index.
The values shown in the Index Histogram table derive from the latest statistics for the selected index. If the index statistics are out of date, these values are also outdated. Check the Last Updated statistic on the Index Details section for the date when statistics were last collected. Use the Update Statistics SQL command to re-collect statistics.
Each series in the table corresponds to one sample value from the first column in the index. The table shows the number of rows in the table that have that value.
Example:
If the selected index is on a Name column, the chart may display the following values:
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ABRAHAM: 5
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GEORGE: 20
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PETER: 25
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STEVEN: 30
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ZACH: 20
This means that five of the people have a name that is alphabetically before or equal to ABRAHAM, 20 people are between ABRAHAM and GEORGE, 25 people are between GEORGE and PETER, and so on.
This chart can be used for identifying skewed indexes, namely: indexes that have a very uneven distribution of data. For example, if 95% of the table has the same value for a key, it is difficult for SQL Azure to determine if it is useful index. Searches on values that fall in the 5% might find the index very useful, but searching on the value that occurs 95% of the time are not so useful.
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