Merge pull request #30249 from CarlRabeler/dtu-s

dtu-s

articles/sql-database/sql-database-service-tiers.md

@@ -19,7 +19,9 @@
 
 # SQL Database options and performance: Understand what's available in each service tier
 
-[Azure SQL Database](sql-database-technical-overview.md) has multiple service tiers to handle different workloads. You can [change service tiers](sql-database-scale-up.md) at any time with minimal downtime to your application (generally averaging under four seconds). You can also [create a single database](sql-database-get-started.md) with defined characteristics and pricing. Or you can manage multiple databases by [creating an elastic database pool](sql-database-elastic-pool-create-portal.md). In both cases, the tiers include **Basic**, **Standard**, and **Premium**. Database options in these tiers are similar for standalone databases and elastic pools, but there are additional considerations for elastic pools. This article provides detail of service tiers for standalone databases and elastic pools.
+[Azure SQL Database](sql-database-technical-overview.md) offers three service tiers with multiple performance levels to handle different workloads. Each performance level provides an increasing set of resources designed to deliver increasingly higher throughput. You can manage each database in its own [service tier](sql-database-service-tiers.md#standalone-database-service-tiers-and-performance-levels) with its own performance level. You can also manage multiple databases in an [elastic pool](sql-database-service-tiers.md#elastic-pool-service-tiers-and-performance-in-edtus) with a shared set of resources. The resources available for standalone databases are expressed in terms of Database Transaction Units (DTUs) and for elastic pools in terms of elastic DTUs or eDTUs. For more on DTUs and eDTUs, see [What is a DTU](sql-database-what-is-a-DTU.md). 
+
+In both cases, the service tiers include **Basic**, **Standard**, and **Premium**. Database options in these tiers are similar for standalone databases and elastic pools, but there are additional considerations for elastic pools. This article provides detail of service tiers for standalone databases and elastic pools.
 
 ## Service tiers and database options
 Basic, Standard, and Premium service tiers all have an uptime SLA of 99.99% and offer predictable performance, flexible business continuity options, security features, and hourly billing. The following table provides examples of the tiers best suited for different application workloads.
@@ -39,25 +41,19 @@ Performance characteristics listed here apply to databases created using [SQL Da
 
 [AZURE.INCLUDE [SQL DB service tiers table](../../includes/sql-database-service-tiers-table.md)]
 
-For a better understanding of DTUs, see the [DTU section](#understanding-dtus) in this topic.
-
 >[AZURE.NOTE] For a detailed explanation of all other rows in this service tiers table, see [Service tier capabilities and limits](sql-database-performance-guidance.md#service-tier-capabilities-and-limits).
 
 ## Elastic pool service tiers and performance in eDTUs
 In addition to creating and scaling a standalone database, you also have the option of managing multiple databases within an [elastic pool](sql-database-elastic-pool.md). All the databases in an elastic pool share a common set of resources. The performance characteristics are measured by *elastic Database Transaction Units* (eDTUs). As with standalone databases, pools come in three service tiers: **Basic**, **Standard**, and **Premium**. For pools, these three service tiers still define the overall performance limits and several features.
 
-Pools allow databases to share and consume DTU resources without needing to assign a specific performance level to each databases in the pool. For example, a standalone database in a Standard pool can go from using 0 eDTUs to the maximum database eDTU you set up when you configure the pool. Pools allow multiple databases with varying workloads to efficiently use eDTU resources available to the entire pool. See [Price and performance considerations for an elastic pool](sql-database-elastic-pool-guidance.md) for details.
+Pools allow databases to share and consume DTU resources without needing to assign a specific performance level to each database in the pool. For example, a standalone database in a Standard pool can go from using 0 eDTUs to the maximum database eDTU you set up when you configure the pool. Pools allow multiple databases with varying workloads to efficiently use eDTU resources available to the entire pool. See [Price and performance considerations for an elastic pool](sql-database-elastic-pool-guidance.md) for details.
 
 The following table describes the characteristics of pool service tiers.
 
 [AZURE.INCLUDE [SQL DB service tiers table for elastic pools](../../includes/sql-database-service-tiers-table-elastic-db-pools.md)]
 
 Each database within a pool also adheres to the standalone database characteristics for that tier. For example, the Basic pool has a limit for max sessions per pool of 4800 - 28800, but an individual database within a Basic pool has a database limit of 300 sessions.
 
-## Understanding DTUs
-
-[AZURE.INCLUDE [SQL DB DTU description](../../includes/sql-database-understanding-dtus.md)]
-
 ## Choosing a service tier
 
 To decide on a service tier, start by determining whether the database should be a standalone database or be part of an elastic pool. 

articles/sql-database/sql-database-what-is-a-dtu.md

@@ -0,0 +1,59 @@
+<properties
+	pageTitle="SQL Database: What is a DTU? | Microsoft Azure"
+	description="Understanding what an Azure SQL Database transaction unit is."
+	keywords="database options,database performance"
+	services="sql-database"
+	documentationCenter=""
+	authors="CarlRabeler"
+	manager="jhubbard"
+	editor="CarlRabeler"/>
+
+<tags
+	ms.service="sql-database"
+	ms.devlang="na"
+	ms.topic="get-started-article"
+	ms.tgt_pltfrm="na"
+	ms.workload="NA"
+	ms.date="09/06/2016"
+	ms.author="carlrab"/>
+
+# Explaining Database Transaction Units (DTUs) and elastic Database Transaction Units (eDTUs)
+
+This article explains Database Transaction Units (DTUs) and elastic Database Transaction Units (eDTUs) and what happens when you hit the maximum DTUs or eDTUs.  
+
+## What are Database Transaction Units (DTUs)
+
+A DTU is a unit of measure of the resources that are guaranteed to be available to a standalone Azure SQL database at a specific performance level within a [standalone database service tier](sql-database-service-tiers.md#standalone-database-service-tiers-and-performance-levels). A DTU is a blended measure of CPU, memory, and data I/O and transaction log I/O in a ratio determined by an OLTP benchmark workload designed to be typical of real-world OLTP workloads. Doubling the DTUs by increasing the performance level of a database equates to doubling the set of resource available to that database. For example, a Premium P11 database with 1750 DTUs provides 350x more DTU compute power than a Basic database with 5 DTUs. To understand the methodology behind the OLTP benchmark workload used to determine the DTU blend, see [SQL Database benchmark overview](sql-database-benchmark-overview.md).
+
+![Intro to SQL Database: Single database DTUs by tier and level](./media/sql-database-what-is-a-dtu/single_db_dtus.png)
+
+You can [change service tiers](sql-database-scale-up.md) at any time with minimal downtime to your application (generally averaging under four seconds). For many businesses and apps, being able to create databases and dial single database performance up or down on demand is enough, especially if usage patterns are relatively predictable. But if you have unpredictable usage patterns, it can make it hard to manage costs and your business model. For this scenario, you use an elastic pool with a certain number of eDTUs.
+
+## What are elastic Database Transaction Units (eDTUs)
+
+An eDTU is a unit of measure of the set of resources (DTUs) that can be shared between a set of databases on an Azure SQL server - called an [elastic pool](sql-database-elastic-pool.png). Elastic pools provide a simple cost effective solution to manage the performance goals for multiple databases that have widely varying and unpredictable usage patterns. See [elastic pools and service tiers](sql-database-service-tiers.md#elastic-pool-service-tiers-and-performance-in-edtus) for more information.
+
+![Intro to SQL Database: eDTUs by tier and level](./media/sql-database-what-is-a-dtu/sqldb_elastic_pools.png)
+
+A pool is given a set number of eDTUs, for a set price. Within the pool, individual databases are given the flexibility to auto-scale within set parameters. Under heavy load, a database can consume more eDTUs to meet demand. Databases under light loads consume less, and databases under no load consume no eDTUs. Provisioning resources for the entire pool rather than for single databases simplifies your management tasks. Plus you have a predictable budget for the pool.
+
+Additional eDTUs can be added to an existing pool with no database downtime or no impact on the databases in the elastic pool. Similarly, if extra eDTUs are no longer needed they can be removed from an existing pool at any point in time. You can add or subtract databases to the pool. If a database is predictably under-utilizing resources, move it out.
+
+## How can I determine the number of DTUs needed by my workload?
+
+If you are looking to migrate an existing on-premises or SQL Server virtual machine workload to Azure SQL Database, you can use the [DTU Calculator](http://dtucalculator.azurewebsites.net/) to approximate the number of DTUs needed. For an existing Azure SQL Database workload, you can use [SQL Database Query Performance Insight](sql-database-query-performance.md) to understand your database resource consumption (DTUs) to get deeper insight into how to optimize your workload. You can also use the [sys.dm_db_ resource_stats](https://msdn.microsoft.com/library/dn800981.aspx) DMV to get the resource consumption information for the last one hour. Alternatively, the catalog view [sys.resource_stats](http://msdn.microsoft.com/library/dn269979.aspx) can also be queried to get the same data for the last 14 days, although at a lower fidelity of five-minute averages.
+
+## How do I know if I could benefit from an elastic pool of resources?
+
+Pools are suited for a large number of databases with specific utilization patterns. For a given database, this pattern is characterized by low average utilization with relatively infrequent utilization spikes. SQL Database automatically evaluates the historical resource usage of databases in an existing SQL Database server and recommends the appropriate pool configuration in the Azure portal. For more information, see [when should an elastic database pool be used?](sql-database-elastic-pool-guidance.md)
+
+## What happens when I hit my maximum DTUs
+
+Performance levels are calibrated and governed to provide the needed resources to run your database workload up to the max limits allowed for your selected service tier/performance level. If your workload is hitting the limits in one of CPU/Data IO/Log IO limits, you continue to receive the resources at the maximum allowed level, but you are likely to see increased latencies for your queries. These limits do not result in any errors, but rather a slowdown in the workload, unless the slowdown becomes so severe that queries start timing out. If you are hitting limits of maximum allowed concurrent user sessions/requests (worker threads), you see explicit errors. See [Azure SQL Database resource limits](sql-database-resource-limits.md) for information on limit on resources other than CPU, memory, data I/O, and transaction log I/O.
+
+## Next steps
+
+- See [Service tier](sql-database-service-tiers.md) for information on the DTUs and eDTUs available for standalone databases and for elastic pools.
+- See [Azure SQL Database resource limits](sql-database-resource-limits.md) for information on limit on resources other than CPU, memory, data I/O, and transaction log I/O.
+- See [SQL Database Query Performance Insight](sql-database-query-performance.md) to understand your (DTUs) consumption.
+- See [SQL Database benchmark overview](sql-database-benchmark-overview.md) to understand the methodology behind the OLTP benchmark workload used to determine the DTU blend.