# Analyzing queries with the Top SQL tab in Performance Insights
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In the Amazon RDS Performance Insights dashboard, you can find information about running and recent queries in the **Top SQL** tab in the **Top dimensions** table. You can use this information to tune your queries.

**Topics**
+ [Overview of the Top SQL tab](#USER_PerfInsights.UsingDashboard.Components.AvgActiveSessions.TopLoadItemsTable.TopSQL)
+ [Accessing more SQL text in the Performance Insights dashboard](USER_PerfInsights.UsingDashboard.SQLTextSize.md)
+ [Viewing SQL statistics in the Performance Insights dashboard](USER_PerfInsights.UsingDashboard.AnalyzeDBLoad.AdditionalMetrics.AnalyzingSQLLevel.md)

## Overview of the Top SQL tab
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By default, the **Top SQL** tab shows the 25 queries that are contributing the most to DB load. To help tune your queries, you can analyze information such as the query text and SQL statistics. You can also choose the statistics that you want to appear in the **Top SQL** tab.

**Topics**
+ [SQL text](#USER_PerfInsights.UsingDashboard.Components.AvgActiveSessions.TopLoadItemsTable.TopSQL.text)
+ [SQL statistics](#USER_PerfInsights.UsingDashboard.Components.AvgActiveSessions.TopLoadItemsTable.TopSQL.statistics)
+ [Load by waits (AAS)](#USER_PerfInsights.UsingDashboard.Components.AvgActiveSessions.TopLoadItemsTable.TopSQL.Load-by-waits)
+ [View SQL information](#USER_PerfInsights.UsingDashboard.Components.AvgActiveSessions.TopLoadItemsTable.TopSQL.SQL-information)
+ [Choose statistics preferences](#USER_PerfInsights.UsingDashboard.Components.AvgActiveSessions.TopLoadItemsTable.TopSQL.Preferences)

### SQL text
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By default, each row in the **Top SQL** table shows 500 bytes of text for each statement. 

![SQL text](http://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/images/sql-text-apg.png)


To learn how to see more than the default 500 bytes of SQL text, see [Accessing more SQL text in the Performance Insights dashboard](USER_PerfInsights.UsingDashboard.SQLTextSize.md).

A *SQL digest* is a composite of multiple actual queries that are structurally similar but might have different literal values. The digest replaces hardcoded values with a question mark. For example, a digest might be `SELECT * FROM emp WHERE lname= ?`. This digest might include the following child queries:

```
SELECT * FROM emp WHERE lname = 'Sanchez'
SELECT * FROM emp WHERE lname = 'Olagappan'
SELECT * FROM emp WHERE lname = 'Wu'
```

To see the literal SQL statements in a digest, select the query, and then choose the plus symbol (\+). In the following example, the selected query is a digest.

![Selected SQL digest](http://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/images/perf_insights_4b.png)


**Note**  
A SQL digest groups similar SQL statements, but doesn't redact sensitive information.

### SQL statistics
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*SQL statistics* are performance-related metrics about SQL queries. For example, Performance Insights might show executions per second or rows processed per second. Performance Insights collects statistics for only the most common queries. Typically, these match the top queries by load shown in the Performance Insights dashboard. 

Every line in the **Top SQL** table shows relevant statistics for the SQL statement or digest, as shown in the following example.

![Top SQL](http://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/images/perf_insights_4.png)


Performance Insights can report `0.00` and `-` (unknown) for SQL statistics. This situation occurs under the following conditions:
+ Only one sample exists. For example, Performance Insights calculates rates of change for Aurora PostgreSQL queries based on multiple samples from the `pg_stat_statements` view. When a workload runs for a short time, Performance Insights might collect only one sample, which means that it can't calculate a rate of change. The unknown value is represented with a dash (`-`).
+ Two samples have the same values. Performance Insights can't calculate a rate of change because no change has occurred, so it reports the rate as `0.00`.
+ An Aurora PostgreSQL statement lacks a valid identifier. PostgreSQL creates a identifier for a statement only after parsing and analysis. Thus, a statement can exist in the PostgreSQL internal in-memory structures with no identifier. Because Performance Insights samples internal in-memory structures once per second, low-latency queries might appear for only a single sample. If the query identifier isn't available for this sample, Performance Insights can't associate this statement with its statistics. The unknown value is represented with a dash (`-`).

For a description of the SQL statistics for the Aurora engines, see [SQL statistics for Performance Insights](sql-statistics.md).

### Load by waits (AAS)
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In **Top SQL**, the **Load by waits (AAS)** column illustrates the percentage of the database load associated with each top load item. This column reflects the load for that item by whatever grouping is currently selected in the **DB Load Chart**. For more information about Average active sessions (AAS), see [Average active sessions](USER_PerfInsights.Overview.ActiveSessions.md#USER_PerfInsights.Overview.ActiveSessions.AAS).

For example, you might group the **DB load** chart by wait states. You examine SQL queries in the top load items table. In this case, the **DB Load by Waits** bar is sized, segmented, and color-coded to show how much of a given wait state that query is contributing to. It also shows which wait states are affecting the selected query.

![DB load by waits](http://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/images/perf_insights_6.png)


### View SQL information
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In the **Top SQL** table, you can open a statement to view its information. The information appears in the bottom pane.

![Top SQL table with literal query selected](http://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/images/perf-insights-sql-ids-open.png)


The following types of identifiers (IDs) that are associated with SQL statements:
+ **Support SQL ID** – A hash value of the SQL ID. This value is only for referencing a SQL ID when you are working with AWS Support. AWS Support doesn't have access to your actual SQL IDs and SQL text.
+ **Support Digest ID** – A hash value of the digest ID. This value is only for referencing a digest ID when you are working with AWS Support. AWS Support doesn't have access to your actual digest IDs and SQL text.

### Choose statistics preferences
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You can control the statistics displayed in the **Top SQL** tab by choosing the **Preferences** icon.

![Statistics preferences](http://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/images/perf-insights-sql-ids-preferences-icon.png)


When you choose the **Preferences** icon, the **Preferences** window opens. The following screenshot is an example of the **Preferences** window.

![Preferences window](http://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/images/perf-insights-sql-ids-preferences.png)


To enable the statistics that you want to appear in the **Top SQL** tab, use your mouse to scroll to the bottom of the window, and then choose **Continue**. 

For more information about per-second or per-call statistics for the Aurora engines, see the engine specific SQL statistics section in [SQL statistics for Performance Insights](sql-statistics.md)