qr code maker for excel Figure 3-1. Pivot table in Excel in VS .NET

Creation QR Code in VS .NET Figure 3-1. Pivot table in Excel

Figure 3-1. Pivot table in Excel
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Figure 3-2 has a pivot chart, showing graphically the distribution of the PAGEIOLATCH_SH wait type over the input period.
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Figure 3-2. Pivot chart 1 in Excel
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The PAGEIOLATCH_SH wait type indicates waits on I/O for read operations. You can clearly see that, in our case, there are dramatic peaks every day around noon. Figure 3-3 has a pivot chart, showing graphically the distribution of all top wait types.
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Figure 3-3. Pivot chart 2 in Excel
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Again, you can see that most waits occur around noon, daily. As an example of how handy the analysis of interval waits can be, in one of my tuning projects I found high peaks of I/O latches every four hours that lasted for quite a while (almost the whole four hours), and then dropped. Naturally, in such a case you look for activities that run on a scheduled basis. Sure enough, the "criminal" was isolated. It was a scheduled job that invoked the sp_updatestats stored procedure against every database every four hours and ran for almost four hours. This stored procedure is used to update statistics globally at the database level. Statistics are histograms maintained for columns that the optimizer uses to determine selectivity of queries, density of joins, and so on. Apparently, in this case some years prior a query didn't perform well because of a lack of up-to-date statistics on a particular indexed column. The customer got a recommendation back then to refresh statistics, and running the stored procedure seemed to solve the problem. Since then, the customer had been running sp_updatestats globally every four hours. Note that SQL Server automatically creates and updates statistics. Typically, the automatic maintenance of statistics is sufficient, and you should intervene manually only in special cases. And if you do intervene manually, do not use sp_updatestats globally! The sp_updatestats stored procedure is useful mainly to refresh statistics globally after an upgrade of the product, or after attaching a database from an earlier version of the product or service pack level. Ironically, when the problem was found, the query that was the trigger for creating the job was not even used anymore in the system. We simply removed the job and let SQL Server use its automatic maintenance of statistics. Naturally, the graph of I/O latches simply flattened and the performance problem was gone.
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Correlate Waits with Queues
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Once you identify the top waits at the instance level, you should correlate them with queues to identify the problematic resources. You mainly use System Monitor for this task. For example, if you
identified I/O-related waits in the previous step, you would check the different I/O queues, cache hit ratios, and memory counters. There should be fewer than two I/O commands waiting on an I/O queue on average per spindle (disk). Cache hit ratios should be as high as possible. As for memory, it is tightly related to I/O because the more memory you have, the more time pages (data and execution plans) can remain in cache, reducing the need for physical I/O. However, if you have I/O issues, how do you know if adding memory will really help You need to be familiar with the tools that would help you make the right choice. For example, the counter SQL Server:Buffer Manager Page life expectancy will tell you how many seconds on average a page is expected to remain in cache without reference. Low values indicate that adding memory will allow pages to remain longer in cache, while high values indicate that adding memory won't help you much in this respect. The actual numbers depend on your expectations and the frequency with which you run queries that rely on the same data/execution plans. Typically, numbers greater than several hundred indicate a good state of memory. But let's say that you have very low values in the counter. Does this mean that you have to add memory Adding memory in such a case would probably help, but some queries lack important indexes on the source tables and end up performing excessive I/O that could be avoided with a better index design. With less I/O and less memory pressure, the problem can be eliminated without investing in hardware. Of course, if you continue your analysis and realize that your indexes and queries are tuned well, you would then consider hardware upgrades. Similarly, if you identified other types of waits as the top ones, you would check the relevant queues and resource utilization. For example, if the waits involve compilations/recompilations, you would check the compilations/recompilations and CPU utilization counters, and so on. SQL Server 2005 provides you with a DMV called sys.dm_os_performance_counters containing all the SQL Server object-related counters that you can find in System Monitor. Unfortunately, this DMV doesn't give you the more generic counters, such as CPU utilization, I/O queues, and so on. You have to analyze those externally. For example, when I ran the following query on my system I got the output shown (in abbreviated form ) in Table 3-3: SELECT object_name, counter_name, instance_name, cntr_value, cntr_type FROM sys.dm_os_performance_counters;
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