Using pgAdmin III to Evaluate Queries in VS .NET

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Using pgAdmin III to Evaluate Queries
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While using the EXPLAIN SQL command can provide useful information, the output can sometimes get confusing, especially as queries become more complex Our old friend pgAdmin III comes to the rescue again, providing a great graphical interface for the EXPLAIN command output
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As discussed in 4, the pgAdmin III Query tool can be used to view the query explain plan in a graphical mode Start the Query tool by clicking the SQL icon in the pgAdmin III toolbar In the top window of the Query tool, enter your SQL query command just as normal (without the EXPLAIN keyword) After entering the query, click the Explain Query icon on the toolbar The lower window contains the result as if you used the EXPLAIN command for the query The Data Output tab shows the normal output you are used to seeing from the EXPLAIN command The Explain tab shows a graphical representation of the EXPLAIN output Each query component is shown as a separate icon in the diagram If you click an individual icon, it displays the statistics for that component Figure 11-1 shows a more complex query example displayed in the Explain tab
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Figure 11-1 Using the pgAdmin III Query Explain function
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Performance
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There are lots of components that were generated from this query The SQL query used to produce this output contained two inner joins to join three tables:
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select "Customer""LastName", "Customer""FirstName", "Product""ProductName", "Order""TotalCost" from store"Order" natural inner join store"Customer" natural inner join store"Product";
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By looking at the graphical output, it is much easier to see how each of the components is used to process the query Just as with the EXPLAIN SQL command, you can set the Query tool query explain function to include actual performance data Choosing Query | Explain Options | Analyze enables the ANALYZE keyword for the EXPLAIN command Now when you click an icon in the graphical output, you can view the actual times as well as the estimated times
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THE POSTGRESQLCONF PERFORMANCE PARAMETERS
After query performance, the next biggest performance problem is the PostgreSQL server itself There are many factors, both hardware and software, that can affect the performance of the server as it processes queries and transactions Some of the hardware factors were discussed in 2 Most of the software factors that affect performance revolve around how the PostgreSQL database engine handles queries and utilizes system resources Instead of hard coding these factors into the PostgreSQL program code, developers have added them to the postgresqlconf file so they can be fine-tuned for specific applications This method enables the PostgreSQL developers to suggest default values to use for these parameters, but allows database administrators to customize their own PostgreSQL environment If your database application is in a specialized environment, such as performing lots of complex queries or lots of data inputs and deletes, changing the PostgreSQL server performance is as easy as customizing the performance parameters in the configuration file Of course, the real trick is knowing which parameters to customize and what values to use This has become more of an art form than a science If you ask three database administrators for suggested values, you might possibly get three totally different answers The solution is to become familiar with the parameters that may most likely affect your database environment, and experiment with different values to see what works best in your situation To help that process, this section describes some of the more famous tunable parameters in the PostgreSQL configuration file
Query Tuning
As shown earlier in the Enhancing Query Performance section, PostgreSQL creates a query explain plan for each query executed by the database engine The postgresqlconf
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file contains parameters that can be used to control what components PostgreSQL uses when executing the query explain plan Modifying these parameters can alter the way the database engine processes your queries, and sometimes can help increase the performance of your queries The individual components used by the database engine to process queries are called planner methods Planner methods are the building blocks used within the query explain plan to obtain the result set, as we saw graphically in 10, Figure 10-7 The database engine puts these building blocks together to produce the result set for the query Each icon in the explain query output is a separate planner method The various planner methods used by the PostgreSQL database engine are described in Table 11-1 You can select to disable individual planner methods in the database engine to force the database engine to utilize a different planner method combination to produce the result set The Query Tuning section of the postgresqlconf configuration file contains entries for each of the planner methods (see 3) To disable a particular planner method, alter the appropriate setting in the postgresqlconf configuration file:
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