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  • How the number of indexes built on a table can impact performances?

    - by Davide Mauri
    We all know that putting too many indexes (I’m talking of non-clustered index only, of course) on table may produce performance problems due to the overhead that each index bring to all insert/update/delete operations on that table. But how much? I mean, we all agree – I think – that, generally speaking, having many indexes on a table is “bad”. But how bad it can be? How much the performance will degrade? And on a concurrent system how much this situation can also hurts SELECT performances? If SQL Server take more time to update a row on a table due to the amount of indexes it also has to update, this also means that locks will be held for more time, slowing down the perceived performance of all queries involved. I was quite curious to measure this, also because when teaching it’s by far more impressive and effective to show to attended a chart with the measured impact, so that they can really “feel” what it means! To do the tests, I’ve create a script that creates a table (that has a clustered index on the primary key which is an identity column) , loads 1000 rows into the table (inserting 1000 row using only one insert, instead of issuing 1000 insert of one row, in order to minimize the overhead needed to handle the transaction, that would have otherwise ), and measures the time taken to do it. The process is then repeated 16 times, each time adding a new index on the table, using columns from table in a round-robin fashion. Test are done against different row sizes, so that it’s possible to check if performance changes depending on row size. The result are interesting, although expected. This is the chart showing how much time it takes to insert 1000 on a table that has from 0 to 16 non-clustered indexes. Each test has been run 20 times in order to have an average value. The value has been cleaned from outliers value due to unpredictable performance fluctuations due to machine activity. The test shows that in a  table with a row size of 80 bytes, 1000 rows can be inserted in 9,05 msec if no indexes are present on the table, and the value grows up to 88 (!!!) msec when you have 16 indexes on it This means a impact on performance of 975%. That’s *huge*! Now, what happens if we have a bigger row size? Say that we have a table with a row size of 1520 byte. Here’s the data, from 0 to 16 indexes on that table: In this case we need near 22 msec to insert 1000 in a table with no indexes, but we need more that 500msec if the table has 16 active indexes! Now we’re talking of a 2410% impact on performance! Now we can have a tangible idea of what’s the impact of having (too?) many indexes on a table and also how the size of a row also impact performances. That’s why the golden rule of OLTP databases “few indexes, but good” is so true! (And in fact last week I saw a database with tables with 1700bytes row size and 23 (!!!) indexes on them!) This also means that a too heavy denormalization is really not a good idea (we’re always talking about OLTP systems, keep it in mind), since the performance get worse with the increase of the row size. So, be careful out there, and keep in mind the “equilibrium” is the key world of a database professional: equilibrium between read and write performance, between normalization and denormalization, between to few and too may indexes. PS Tests are done on a VMWare Workstation 7 VM with 2 CPU and 4 GB of Memory. Host machine is a Dell Precsioni M6500 with i7 Extreme X920 Quad-Core HT 2.0Ghz and 16Gb of RAM. Database is stored on a SSD Intel X-25E Drive, Simple Recovery Model, running on SQL Server 2008 R2. If you also want to to tests on your own, you can download the test script here: Open TestIndexPerformance.sql

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  • Fun tips with Analytics

    - by user12620172
    If you read this blog, I am assuming you are at least familiar with the Analytic functions in the ZFSSA. They are basically amazing, very powerful and deep. However, you may not be aware of some great, hidden functions inside the Analytic screen. Once you open a metric, the toolbar looks like this: Now, I’m not going over every tool, as we have done that before, and you can hover your mouse over them and they will tell you what they do. But…. Check this out. Open a metric (CPU Percent Utilization works fine), and click on the “Hour” button, which is the 2nd clock icon. That’s easy, you are now looking at the last hour of data. Now, hold down your ‘Shift’ key, and click it again. Now you are looking at 2 hours of data. Hold down Shift and click it again, and you are looking at 3 hours of data. Are you catching on yet? You can do this with not only the ‘Hour’ button, but also with the ‘Minute’, ‘Day’, ‘Week’, and the ‘Month’ buttons. Very cool. It also works with the ‘Show Minimum’ and ‘Show Maximum’ buttons, allowing you to go to the next iteration of either of those. One last button you can Shift-click is the handy ‘Drill’ button. This button usually drills down on one specific aspect of your metric. If you Shift-click it, it will display a “Rainbow Highlight” of the current metric. This works best if this metric has many ‘Range Average’ items in the left-hand window. Give it a shot. Also, one will sometimes click on a certain second of data in the graph, like this:  In this case, I clicked 4:57 and 21 seconds, and the 'Range Average' on the left went away, and was replaced by the time stamp. It seems at this point to some people that you are now stuck, and can not get back to an average for the whole chart. However, you can actually click on the actual time stamp of "4:57:21" right above the chart. Even though your mouse does not change into the typical browser finger that most links look like, you can click it, and it will change your range back to the full metric. Another trick you may like is to save a certain view or look of a group of graphs. Most of you know you can save a worksheet, but did you know you could Sync them, Pause them, and then Save it? This will save the paused state, allowing you to view it forever the way you see it now.  Heatmaps. Heatmaps are cool, and look like this:  Some metrics use them and some don't. If you have one, and wish to zoom it vertically, try this. Open a heatmap metric like my example above (I believe every metric that deals with latency will show as a heatmap). Select one or two of the ranges on the left. Click the "Change Outlier Elimination" button. Click it again and check out what it does.  Enjoy. Perhaps my next blog entry will be the best Analytic metrics to keep your eyes on, and how you can use the Alerts feature to watch them for you. Steve 

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  • iphone - getting the button id in a segmented control

    - by Mike
    I am trying to create something that uses the idea of the UIPopOverController, I mean, have that speech bubble anchor pointing to the button who triggered the method. The problem is that I am using a UISegmentedControl... How do I get the id of the button that was tapped on a UISegmentedControl, so I can determine its position and generate the anchor? thanks for any help.

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  • question about sorting

    - by skydoor
    Bubble sort is O(n) at best, O(n^2) at worst, and its memory usage is O(1) . Merge sort is always O(n log n), but its memory usage is O(n). Which algorithm we would use to implement a function that takes an array of integers and returns the max integer in the collection, assuming that the length of the array is less than 1000. What if the array length is greater than 1000?

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  • Bubbling scroll events from a ListView to its parent

    - by emddudley
    In my WPF application I have a ListView whose ScrollViewer.VerticalScrollBarVisibility is set to Disabled. It is contained within a ScrollViewer. When I attempt to use the mouse wheel over the ListView, the outer ScrollViewer does not scroll because the ListView is capturing the scroll events. How can I force the ListView to allow the scroll events to bubble up to the ScrollViewer?

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  • How can I programmatically tell if a caught IOException is because the file is being used by another

    - by Paul K
    When I open a file, I want to know if it is being used by another process so I can perform special handling; any other IOException I will bubble up. An IOException's Message property contains "The process cannot access the file 'foo' because it is being used by another process.", but this is unsuitable for programmatic detection. What is the safest, most robust way to detect a file being used by another process?

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  • jquery event namespace bubbling issue

    - by Adrian Adkison
    Hi, I stumbled upon an issue with event namespacing while developing a jQuery plugin. here is the html <div class="parent"> <div class="child"> </div> </div> <a class="btn-a">trigger a</a> <a class="btn-b">trigger b</a> <a class="btn-c">trigger c</a> Here is the jQuery jQuery('#content div.child') .bind('child.a',function(){alert('a-child');}) .bind('child.b',function(){alert('b-child');}) .bind('child.c',function(){alert('c-child');}); jQuery('#content div.parent') .bind('child.b',function(){alert('b-parent');}) .bind('child.c',function(){alert('c-parent');}); jQuery('a.btn-a') .click(function(){ jQuery('#content div.child').trigger('a.a'); }); jQuery('a.btn-b') .click(function(){ jQuery('#content div.child').trigger('a.b'); }); jQuery('a.btn-c') .click(function(){ jQuery('#content div.child').trigger('a.c'); }); In sum, I have attached a namespaced event listener to the child and parent and created three buttons that trigger each of the events(a.a, a.b, a.c). Note the parent is only listening to a.b and a.c. When I click on the button that triggers a.a on the child, only the div.child listener for a.a is fired, but the entire 'a' namespace event bubbles up to div.parent listeners, a.b and a.c, and triggers them. My question is, how would I still use event namespacing but only have the intended event bubble up(i.e. a.a is the only event that fires for both child and parent). I am aware of stopPropagation and stopImmediatePropagation. I would not want to put these on the child a.b and a.c listeners because there are times when i do want them to bubble. For instance when I trigger 'a.b' on the child, I would expect the 'a.b' and only the 'a.b' event to be handled by the child and the parent. Thanks

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  • java api design - NULL or Exception

    - by srini.venigalla
    Is it better to return a null value or throw an exception from an API method? Returning a null requires ugly null checks all over, and cause a major quality problem if the return is not checked. Throwing an exception forces the user to code for the faulty condition, but since Java exceptions bubble up and force the caller code to handle them, in general, using custom exceptions may be a bad idea (specifically in java). Any sound and practical advice?

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  • Change Label Control Property Based on Data from SqlDataSource Inside a Repeater

    - by Furqan Muhammad Khan
    I am using a repeater control to populate data from SqlDataSource into my custom designed display-box. <asp:Repeater ID="Repeater1" runat="server" DataSourceID="SqlDataSource1" OnDataBinding="Repeater_ItemDataBound"> <HeaderTemplate> </HeaderTemplate> <ItemTemplate> <div class="bubble-content"> <div style="float: left;"> <h2 class="bubble-content-title"><%# Eval("CommentTitle") %></h2> </div> <div style="text-align: right;"> <asp:Label ID="lbl_category" runat="server" Text=""><%# Eval("CommentType") %> </asp:Label> </div> <div style="float: left;"> <p><%# Eval("CommentContent") %></p> </div> </div> </ItemTemplate> <FooterTemplate> </FooterTemplate> </asp:Repeater> <asp:SqlDataSource ID="mySqlDataSource" runat="server" ConnectionString="<%$ ConnectionStrings:myConnectionString %>" SelectCommand="SELECT [CommentTitle],[CommentType],[CommentContent] FROM [Comments] WHERE ([PostId] = @PostId)"> <SelectParameters> <asp:QueryStringParameter Name="PostId" QueryStringField="id" Type="String" /> </SelectParameters> </asp:SqlDataSource> Now, there can be three types of "CommentTypes" in the database. I want to change the CssClass property of "lbl_category" based on the value of [CommentType]. I tried doing this: <asp:Label ID="lbl_category" runat="server" CssClass="<%# Eval("CommentType") %>" Text=""><%# Eval("CommentType") %></asp:Label> But this gives an error: "The server control is not well formed" and haven't been able to find a way to achieve this in the code behind. Can someone please help?

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  • What should students be taught first when first learning sorting algorithms?

    - by Johan
    If you were a programming teacher and you had to choose one sorting algorithm to teach your students which one would it be? I am asking for only one because I just want to introduce the concept of sorting. Should it be the bubble sort or the selection sort? I have noticed that these two are taught most often. Is there another type of sort that will explain sorting in an easier to understand way?

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  • Bubbling up events . .

    - by oo
    I have multiple layers in an application and i find myself having to bubble up events to the GUI layer for doing status bar changes, etc . . I find myself having to write repeated coded where each layer simply subscribes to events from the lower layer and then in the call back simply raise an event up the chain. Is there a more efficient way of doing this?

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  • Google Maps for Absolute Dummies

    - by decbrad
    Hi there, I just signed up for a Google Maps API key and was hoping for a wizard style application for setting up the map (not a static one), unfortunately I was immediately blinded by science! Can anyone point me to a tutorial where I can find out how to create a simple google map and place a callout bubble including am image of the office and address details. Thanks in advance Decbrad

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  • how to insert Link in to jquery grid column

    - by kumar
    Hello Friends, Can any one tell me how to insert link in to Jquery grid column,, that is I have a column with Edittype { name: 'Comments', index: 'Comments', editable: true, editype: 'textarea', editoptions: { rows: "2", cols: "10"} } I need to insert comments in to this.. so if I have link to click on the column so that some popup bubble will come there in the window to enter comments more like user friendly.. can anybody sujjests me on this.. Thanks

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  • In C, during step by step debugging in a function, how can i view the content of an array in the "Autos?" window along with the other variables?

    - by AppsAndGo
    I'm using VS 2012, and I'm working on a bubble sort. After searching I found a nifty trick to see the content of the array in the "Watch 1" tab, (How to view contents of an array while debugging in Code Blocks?), but going from "watch 1" to "Autos" every step to see what's changing in the array isn't practical at all. How can i see the array content within "Autos" along side my other changing variables, where i need it to show?

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  • .NET: How to place my window near the notification area (systray)?

    - by Vilx-
    I'd like to display a little popup window next to the notification area. It's similar to what Outlook/Skype/Live! Messenger/etc does when it displays the notification about a new message. In my case it will have some input controls (textbox, datetimepicker, buttons...) so a simple bubble won't do. The trick is doing this correctly when the user has multiple monitors and/or the taskbar is not located at the bottom of the screen.

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  • CPU/JVM/JBoss 7 slows down over time

    - by lukas
    I'm experiencing performance slow down on JBoss 7.1.1 Final. I wrote simple program that demostrates this behavior. I generate an array of 100,000 of random integers and run bubble sort on it. @Model public class PerformanceTest { public void proceed() { long now = System.currentTimeMillis(); int[] arr = new int[100000]; for(int i = 0; i < arr.length; i++) { arr[i] = (int) (Math.random() * 200000); } long now2 = System.currentTimeMillis(); System.out.println((now2 - now) + "ms took to generate array"); now = System.currentTimeMillis(); bubbleSort(arr); now2 = System.currentTimeMillis(); System.out.println((now2 - now) + "ms took to bubblesort array"); } public void bubbleSort(int[] arr) { boolean swapped = true; int j = 0; int tmp; while (swapped) { swapped = false; j++; for (int i = 0; i < arr.length - j; i++) { if (arr[i] > arr[i + 1]) { tmp = arr[i]; arr[i] = arr[i + 1]; arr[i + 1] = tmp; swapped = true; } } } } } Just after I start the server, it takes approximately 22 seconds to run this code. After few days of JBoss 7.1.1. running, it takes 330 sec to run this code. In both cases, I launch the code when the CPU utilization is very low (say, 1%). Any ideas why? I run the server with following arguments: -Xms1280m -Xmx2048m -XX:MaxPermSize=2048m -Djava.net.preferIPv4Stack=true -Dorg.jboss.resolver.warning=true -Dsun.rmi.dgc.client.gcInterval=3600000 -Dsun.rmi.dgc.server.gcInterval=3600000 -Djboss.modules.system.pkgs=org.jboss.byteman -Djava.awt.headless=true -Duser.timezone=UTC -Djboss.server.default.config=standalone-full.xml -Xrunjdwp:transport=dt_socket,address=8787,server=y,suspend=n I'm running it on Linux 2.6.32-279.11.1.el6.x86_64 with java version "1.7.0_07". It's within J2EE applicaiton. I use CDI so I have a button on JSF page that will call method "proceed" on @RequestScoped component PerformanceTest. I deploy this as separate war file and even if I undeploy other applications, it doesn't change the performance. It's a virtual machine that is sharing CPUs with another machine but that one doesn't consume anything. Here's yet another observation: when the server is after fresh start and I run the bubble sort, It utilizes 100% of one processor core. It never switches to another core or drops utilization below 95%. However after some time the server is running and I'm experiencing the performance problems, the method above is utilizing CPU core usually 100%, however I just found out from htop that this task is being switched very often to other cores. That is, at the beginning it's running on core #1, after say 2 seconds it's running on #5 then after say 2 seconds #8 etc. Furthermore, the utilization is not kept at 100% at the core but sometimes drops to 80% or even lower. For the server after fresh start, even though If I simulate a load, it never switches the task to another core.

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