The SQL Query Tuner will quickly and easily identify SQL queries that cause poor database performance via database profiling and display a graphical visualization of wait time analysis. Cloud support varies greatly from tool to tool. This defines the order in which the tables are joined. It is often a trial-and-error process where different queries are tested to see which one offers the best performance, while still returning the sought after data. EverSQL is an online SQL query optimizer for developers and database administrators. Learn the basics of data modeling and how it impacts performance. Query optimizers are sometimes built into database management systems but external, third-party tools are often thought to offer better performance results. Queries are submitted to SQL Server using the SQL language (or T-SQL, the Microsoft SQL Server extension to SQL). So it’s actually the functionality of the execution engine that is being implemented in the execution plans being created by the Query Optimizer, that is, the execution engine implements a certain number of different algorithms and it is from these algorithms that the Query Optimizer must choose, when formulating its execution plans. You can read Benjamin’s blog at www.benjaminnevarez.com or reach him by e-mail at admin at benjaminnevarez dot com and on twitter @BenjaminNevarez. This might not seem significant, but if you compare the cost of each query, via the Query cost (relative to the batch) information at the top of each plan, you will see that there might be a price to pay for overruling the Query Optimizer, as it has found the hinted query to be more expensive. However, some complex queries may have thousands or even millions of possible execution plans and, while the SQL Server Query Optimizer can typically consider a large number of candidate execution plans, it cannot perform an exhaustive search of all the possible plans for every query. All of the tools reviewed here will at least to that but some offer much more functionality. As you may know, the tool—which was first launched first launched with Microsoft SQL Server 2005—is used for configuring, managing, and administering all components within Microsoft SQL Server. You can easily view recommended indexes, create and modify indexes, and detect and update old statistics. You can use it to experiment and find the best solution for your statements. All code has been tested for these databases on both SQL Server 2008 and SQL Server 2008 R2. Visually tune complex SQL queries Load test in simulated production environments Streamline SQL query tuning … This should help you appreciate the importance of a query optimizer. At the core of the SQL Server Database Engine are two major components: the Storage Engine and the Query Processor, also called the Relational Engine. It refers to the process of calculating the optimal join order, that is, the order in which the necessary tables are joined, when executing a query. The query optimizer determines the most efficient way to execute a SQL statement after considering many factors related to the objects referenced and the conditions specified in the query. SQL query optimization allows one to fine-tune queries so that they return the right data as quickly as possible. Once the query is optimized, the resulting plan is used by the Execution Engine to retrieve the desired data. We’ve also looked at the complexity of the optimization process, including the challenges it faces in exploring the potentially vast search space and accurately estimating cardinality and the cost of candidate execution plans. Two excellent examples of these tools are the Advanced Subnet Calculator and the Kiwi Syslog Server. For more information about the sys.dm_exec_requests DMV and the sys.dm_exec_query_plan DMF, you should go to Books Online. So how does the Query Optimizer analyze all these possible plan combinations? The answer is: it doesn’t. Figure 5 – Properties Window for the Query. The Optimizer is one of the most fascinating components of the Oracle Database, since it is essential to the processing of every SQL statement. The Storage Engine is responsible for reading data between the disk and memory in a manner that optimizes concurrency while maintaining data integrity. As a result, it is clearly extremely important that the set of plans which a query optimizer considers contains plans with low costs. Most of the time, the Query Optimizer does a great job at choosing highly efficient execution plans. This cost estimation depends mostly on the algorithm used by the physical operator, as well as the estimated number of records that will need to be processed; this estimate of the number of records is known as the cardinality estimation. On the other hand, when an estimated plan is requested, the query is naturally not executed, and the plan displayed is simply the plan that SQL Server would most probably use if the query were executed (bearing in mind that a recompile, which we’ll discuss later, may generate a different plan at execution time). Simple right-click anywhere on the execution plan window to display a pop-up window, as shown in Figure 6, and select Show Execution Plan XML…; this will open the XML editor and display the XML plan as shown in Figure 7. We’ll do our best to sort out the essential features that you should be looking for when picking the best tool for your specific needs. We’ve … Knowing what SQL statements to focus on rewriting and having software provide you with recommendations can help you to increase your work rate and make your database run faster. Simply put, SQL query optimization is the act of analyzing SQL queries and determining the most efficient execution mechanism. Likewise, the creation of a new index could make a plan suboptimal, if this index could be used to create a more efficient alternative plan, and enough changes to the database contents may trigger an automatic update of statistics, with the same effect on the existing plan. You can hover the mouse pointer over an arrow to get more information about that data flow, displayed as a tooltip. The language defines how queries can be formed to extract from a database the precise data which is required. In the second result set you will see the following plan (edited to fit the page), which shows the same Hash Aggregate and Index Scan operators displayed earlier in Figure 2: Listing 5 – The result of running Listing 4. Listing 8 – Forcing a specific join order. You can request either an actual or an estimated execution plan for a given query, and either of these two types can be displayed as a graphic, text or XML plan. The first query will show a cost of 3.2405 and the second one will show 5.3462. According to Microsoft’s official documentation, the tool can help you troubleshoot the performance of a specific problem query, tune a large set of queries across one or more databases, perform an exploratory what-if analysis of potential physical design changes, and manage storage space. The extensible architecture of the Cascades Framework has made it much easier for new functionality, such as new transformation rules or physical operators, to be implemented in the Query Optimizer. A free 30-day trial of the whole product—not just the query optimization tool—is available. The SQL Query Tuner is an add-on to the SQL Diagnostic Manager. The Index Analysis uses scoring algorithms to help you determine the best index to support a given query. Different tools offer different features, as you’re about to see. Table Scan, Index Scan or Index Seek), as well as optimize other parts of the query, such as aggregations, subqueries and so on. Thus, for each query it receives, the first job of the query processor is to devise a plan, as quickly as possible, which describes the best possible way to execute said query (or, at the very least, an efficient way). It will show you where adding an index to a table or optimizing table joining, for example, could increase performance. The trailblazers in this field were the Exodus Extensible DBMS Project, and later the Volcano Optimizer generator, the latter of which was defined by Goetz Graefe (who was also involved in the Exodus Project) and William McKenna. Then, we’ll discuss the main features of SQL query optimization tools. It identifies problematic SQL queries via database profiling of wait time analysis. Understand the optimization techniques available in modern data warehouses. This tool will present automatically generated suggested solutions with the SQL query tuning wizard which provide an essential context for tuning SQL queries. In a Nested Loops join, for example, the first accessed table is called the outer table and the second one the inner table. For example, the costing model assumes that every query starts with a cold cache; that is, its data is read from disk and not from memory, and this assumption could lead to costing estimation errors in some cases. It is the process of re-writing SQL statements differently with the goal of improving the performance of the query while still getting the same resulting data set. The reality is that, even after more than 30 years of research, query optimizers are highly complex pieces of software which still face some technical challenges, some of which will be mentioned in the next section. The use of proper indexing is first step to optimise the query. While some SQL query optimization tools are simpler helper applications that require much human assistance, the best systems do most of their work in the background. The main screen will let you view database instances, wait times, query advice, CPU (with warning and critical alerts), memory, disk and sessions. If you already know that stuff, skip ahead to the Query Optimization Tips! You can also see the relative cost of each operator in the plan as a percentage of the overall plan, as shown previously in Figure 2. To write optimal SQL queries that perform well, you need to know how the query optimizer works. Benjamin Nevarez is a SQL Server MVP and independent consultant based in Los Angeles, California who specializes in SQL Server query tuning and optimization. A query optimizer is a critical database management system (DBMS) component that analyzes Structured Query Language (SQL) queries and determines efficient execution mechanisms. In this tip I show how to use the undocumented QUERYRULEOFF hint to help tune a query. Parsing and binding – the query is parsed and bound. SQL developers and database administrators can use the GUI tool to speed up almost any complex database tasks such as designing databases, writing SQL code, comparing databases, synchronizing schemas and data, generating meaningful test data, among others. To get indexing recommendations and to allow the tool to apply advanced query transformations, you can optionally upload you database’s schema structure. The optimizer is built-in software that determines the most efficient method for a statement to access data. The only difference between these three formats is the level of detail of information displayed. This logical tree is then used to run the query optimization process, which roughly consists of the following two steps; Generate possible execution plans – using the logical tree, the Query Optimizer devises a number of possible ways to execute the query i.e. As suggested on the ongoing challenges briefly discussed earlier, join ordering is directly related to the size of the search space as the number of possible plans for a query grows very rapidly depending on the number of tables joined. Notice also how, in addition to the actual number of rows, you can also see the estimated number of rows; this is the Query Optimizer’s cardinality estimation for this operator. However, you will see from the plan shown in Figure 8 that the Query Optimizer actually chose the join order (Sales.Customer JOIN Sales.Individual) JOIN Person.Contact. The first icon is called the result operator; it represents the SELECT statement, and is usually the root element in the plan. The plan may be stored in memory, in the plan cache. Explore performance-related Dynamic Management Objects. Optimizing SQL queries can be done manually, but tools exist to assist in optimizing them. Bushy trees, on the other hand, can take any arbitrary shape, and so the set of bushy trees actually includes the sets of both left-deep and right-deep trees. You can display the graphical plans in SQL Server Management Studio by clicking the Display Estimated Execution Plan or Include Actual Execution Plan buttons from the SQL Editor toolbar, which is enabled by default. A join works with only two tables at a time, so a query requesting data from n tables must be executed as a sequence of n – 1 joins, but it should be noted that the first join does not have to been completed before the next join can be started. a.Create the proper indexes on columns in queries where following Clauses – Where Clause -Group By Clause – Order By Clause And finally, we’ll review the best tools we could find. Of course, we should also bear in mind that this is just the number of permutations for the join order. There are some important steps to use or create index. Query optimizers are sometimes built into database management systems but external, third-party tools are often thought to offer better performance results. EverSQL is an online SQL query optimizer. This is the trial plan. Even supposing that time is not a concern and that the query optimizer can analyze the entire search space without a problem, cardinality and cost estimation errors can still make a a query optimizer select the wrong plan. For example, the cost of the Index Scan is 52% of the cost of the entire plan. As a result of the research that has gone into solving some of those challenges, the Query Optimizer implemented in SQL Server is based on the extensible Cascades Framework architecture, which facilitates the addition of new functionality to the query optimizer, including new operators and transformation rules. The performance (i.e. To perform their job, physical operators implement at least the following three methods: Open(), which causes an operator to be initialized, GetRow() to request a row from the operator, and Close() to shut down the operator once it’s performed its role. We’ll end  with a discussion of join ordering, one of the most complex problems in query optimization, and shows how joining tables in an efficient order improves the performance of a query but, at the same time, can exponentially increase the number of execution plans that should be analyzed by the Query Optimizer. When drilling down, the trend dashboard of a specific database instance shows you in a graphical format the total wait times (or your choice of average or typical day wait times) for users over the course of a month. SQL is one of the most powerful data-handling tools around. Its flagship product called the SolarWinds Network Performance Monitor is viewed by many as one of the very best network bandwidth monitoring software. However, recent versions of Books Online, including that of SQL Server 2008 R2, indicates that all text versions of execution plans will be deprecated in a future version of SQL Server. If you’re running without a data warehouse or separate analytical database for reporting, the live production database is likely your only source for the latest, up-to-date data. The Optimizer determines the most efficient execution plan for each SQL statement based on the structure of the query, the available statistical information about the underlying objects, and all the relevant optimizer and execution features. As the Query Optimizer is working within a time constraint, there’s a chance that the plan selected may be the optimal plan but it is also likely that it may just be something close to the optimal plan. Query optimization is an inherently complex problem, not only in SQL Server but in any other relational database system. Figure 10 shows left-deep and bushy trees for a join of 4 tables. You can generate possible cases and find the best alternative to a given SQL statement by including SQL query rewrites and hint injections. Devart’s dbForge Studio for SQL server is an all-in-one SQL server GUI tool which can be used for SQL Server management, administration, development, data reporting, analysis, optimization, and more. The Hash Aggregate operator is, in turn, performing some operation on this data and sending 575 records to its parent, which you can see by placing the mouse pointer over the arrow between the Hash Aggregate and the SELECT icon. Copyright 1999 - 2020 Red Gate Software Ltd. SQL query optimization is being applied in order to minimize the possibility of your query being the system bottleneck. For example, a logical join can be mapped to a Nested Loops Join, Merge Join, or Hash Join physical operator. Others will support a wider selection and others yet will only support one. Clicking the link will show you a graphical plan, and you can then display the XML plan using the same procedure as explained earlier. Learn how to optimize queries by modifying SQL. Searching, or enumerating candidate plans is just one part of the optimization process. EverSQL can optimize queries in database systems such as MySQL, MariaDB, and PerconaDB. In order to arrive at what it believes to be the best plan for executing a query, the Query Processor performs a number of different steps; the entire query processing process is shown on figure 1-1. So, for example, choosing the SELECT icon and selecting the Properties Window from the View menu (or pressing F4) will show some properties for the entire query, as shown in Figure 5. In addition to learning more about the data flow, you can also hover the mouse pointer over an operator to get more information about it. As such, the Query Optimizer has to select the best possible plan from what may be a very large number of candidate execution plans, and it’s important that it makes a wise choice, as the time it takes to return the results to the user can vary wildly, depending on which plan is selected. You can load this file again, by selecting File > Open in Management Studio, in order to immediately display it as a graphical plan, which will behave exactly as before. As noted earlier, the number of possible join orders in a query increases exponentially with the number of tables. While most SQL query optimizers use estimated plan cost, Plan Explorer can display the actual observed costs. Each of these tasks is delegated to a separate component within the query processor; the Query Optimizer devises the plan and then passes it along to the Execution Engine, which will actually execute the plan and get the results from the database. Specifically, the optimizer needs to make two important decisions regarding joins: The order in which the tables are joined determines the cost and performance of a query. The Query Optimizer must strike a balance between optimization time and plan quality. The Query Processor, as the name suggests, accepts all queries submitted to SQL Server, devises a plan for their optimal execution, and then executes { LOOP | MERGE | HASH } JOINSpecifies all join operations are performed by LOOP JOIN, MERGE JOIN, or H… Operators implement a basic function or operation of the execution engine; for example, a logical join operation could be implemented by any of three different physical join operators: Nested Loops Join, Merge Join or Hash Join. SQL Server Query Engine 101. For SQL Query optimization, what you need, though, is the SolarWinds Database Performance Analyzer (DPA), a database management tool built for SQL query performance monitoring, analysis, and tuning. This data flow is represented by arrows between the operators, and the thickness of the arrows corresponds to the relative number of rows. However, there may be cases when the selected execution plan does not perform as expected. A factorial is the product of all positive integers less than or equal to n; so, for example, for a 5-table join, the number of possible join orders is 5! Now that we’ve got a foundation in the Query Optimizer and how it works its magic, it’s time to consider how we, as users, can interact with it. Since we want everyone to be on the same page as we review the best products, we’ll start off by discussing the what and the shy of SQL query optimization. EverSQL is interesting as it is one of the few online SQL optimization tools. For example, in theory, if we had a 6-table join, a query optimizer would potentially need to evaluate 30,240 possible join orders. Different tree representations of the query will be used throughout the optimization process, and this logical tree will receive different names until it is finally used to initialize the Memo structure, as will be discussed later. As aresult, you’ll gain a better understanding of how SQL Server plans to execute SQL queries and the various performance costs. = 5 x 4 x 3 x 2 x 1 = 120. On that graph, each colour represents an individual SQL statement, giving you a visually appealing representation of which statement takes the longest to run. It is often a trial-and-error process where different queries are tested to see which one offers the best performance, while still returning the sought after data. If needed, graphical plans can be saved to a file by selecting Save Execution Plan As… from the pop-up window shown in Figure 6. Initially, these logical operators will be closely related to the original syntax of the query, and will include such logical operations as “get data from the Customer table”, “get data from the Contact table”, “perform an inner join”, and so on. Despite the fact that query optimization research dates back to the early seventies, challenges in some fundamental areas are still being addressed today. A join combines records from two tables based on some common information, and the predicate which defines which columns are used to join the tables is called a join predicate. A low query cost may not indicate a fast query or the best plan. A query optimizer generates one or more query plans for each query, each of … Thus, the end product of the query optimization process is an execution plan: a tree consisting of a number of physical operators, which contain the algorithms to be performed by the execution engine in order to obtain the desired results from the database. However, when an actual plan is requested, the query needs to be executed, and the plan is then displayed along with the query results. As has already been mentioned, SQL Server uses a cost-based optimizer, and uses a cost estimation model to estimate the cost of each of the candidate plans. There’s no need to run the query again. Figure 6 – Pop-up window on the Execution plan window. OptimizSQL is an online SQL query optimizer for developers and database administrators. The job of the Query Optimizer is to create and assess as many candidate execution plans as possible, within certain criteria, in order to arrive at the best possible plan. Hence, it is always good to know some good and simple ways to optimize your SQL query. Table 2 shows how the number of possible join orders increases as we increase the number of tables, for both left-deep and bushy trees, and I’ll explain how it’s calculated in a moment. Figure 8 – Execution plan for query joining 3 tables. The associative property of a join between tables A, B and C states that: (A JOIN B) JOIN C is equivalent to A JOIN (B JOIN C). Using this tool, you can play back the query profile to see exactly which operators are adding the most load on system resources. You click “Next” and within seconds, you get the optimized version of your query along with some indexing recommendations. For example, Figure 4 shows information about the Index Scan operator; notice that it includes, among other things, data on estimated costing information like the estimated I/O, CPU, operator and subtree costs. The tool works by measuring the query execution time of the various versions of the query (query plans) and picking the one that executes the fastest. As you can see in Table 1-1, there are two commands to get estimated text plans; SET SHOWPLAN_TEXT and SET SHOWPLAN_ALL. Obviously, there are many more operators implemented in the execution engine, and all of them are documented in Books Online if you’re curious about them. In fact, its use is so prevalent that we often refer to database servers as SQL servers. One of the best things about SQL Server Management Studio is its price. Some SQL query optimization tools are able to analyze and optimize cloud-hosted databases such as Microsoft SQL Azure or AWS RDS. The primary way we’ll interact with the Query Optimizer is through execution plans which, as I mentioned earlier, are ultimately trees consisting of a number of physical operators, which in turn contain the algorithms to produce the required results from the database. The plan that the Query Optimizer deems to have the lowest cost of those it’s assessed is selected, and passed along to the Execution Engine; Query execution, plan caching – the query is executed by the Execution Engine, according to the selected plan. While query cost is a useful metric to understand how SQL Server has optimized a particular query, it is important to remember that its primary purpose is to aid the query optimizer in choosing good execution plans. It analyzes a number of candidate execution plans for a given query, estimates the cost of each of these plans and selects the plan with the lowest cost of the choices considered. Because the order of joins is a key factor in controlling the amount of data flowing between each operator in the execution plan, it’s a factor which the Query Optimizer needs to pay close attention to. Again, it’s important to pick one that supports what you have. It is created by SQL Server query optimizer, and provides you with information on how a query will be executed and show you all individual actions that constitute this query.MS SQL Management Studio provides two ways to view Execution Plan: text and graphical. By looking at the resultant execution plan, shown on Figure 8, you can see that the Query Optimizer is not using the same join order as what is specified in the query; it found a more efficient one instead. Step 1 : Use Explain Plan Feature to check cost of query Every programmer have question in mind that from where to start tuning? Most essential components related to performance are as displayed in the below pie chart, SQL & Query Optimization Tools: Take Your Database to the Next Level Writing solid SQL code takes time, but the right SQL & query optimization tools can help you to work much more efficiently. Rather than exhaustively evaluate every single combination, the Query Optimizer tries to narrow the possibilities down to the most likely candidates, using heuristics (some of which we’ve already touched upon) to guide the process. But when complementing it with the SQL query tuner, what you get is one of the best SQL query optimization tools. More tables in a query would equate to a larger chess board. Get the latest news and training with the monthly Redgate UpdateSign up, Using a Public Web Service to Consume SQL Server Build Numbers. Cost estimation models are inherently inexact, as they do not consider all of the hardware conditions, and must necessarily make certain assumptions about the environment. In essence, query optimization is the process of mapping the logical query operations expressed in the tree representation to physical operations, which can be carried out by the execution engine. Figure 4 – Tooltip for the Index Scan operator. The statistics analysis module shows you the impact of compiled and runtime query parameters on performance. The generation of candidate execution plans is performed inside the Query Optimizer using transformation rules, and the use of heuristics limits the number of choices considered in order to keep the optimization time reasonable. 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