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  • full duplex communication over the web w/o flash sockets

    - by aharon
    A web application I'm helping to develop is faced with a well-known problem: we want to be able to let users know of various events and so forth that can occur at any time, essentially at random, and update their view accordingly. Essentially, we need to allow the server to push requests to individual clients, as opposed to the client asking the server. I understand that WebSockets are an effort to address the problem; however, after a bit of looking around into them, I understand that a) very few web browsers currently offer native websocket support; b) to get around this, you either use flash sockets or some sort of AJAX long-polling; c) a special websockets server must be used. Now, we want to offer our service without Flash. And any sort of servers must have some sort of load-balancing capabilities, or at least some software that can do load balancing for them. As of 2008, everyone was saying that Comet-based solutions (e.g., Bayeux) were the way to go for these sort of situations. However, the various protocols seem to have not had much work put into them since then—which leads (finally) to the question. Is Bayeux-flavored Comet still the right tool for jobs like this? If not, what is?

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  • Alternative Python standard library reference

    - by Ender
    I love Python; I absolutely despise its official documentation. Tutorials do not count as library references, but that appears to be what they're attempting. What I really want is the ability to find a class in the standard library and view documentation for all of its properties and methods. Actionscript, MSDN, and Java all do this just fine (although each with their odd quirks). Where is this for python? For example, I wanted to sort a list. mylist.sort(). Awesome. But what if I wanted it sorted in descending order? Official documentation is not - much - help. Or what if I wanted to specify a key function? That's also supported: mylist.sort(key=lamba item: item.customVar)- but documented...where? I understand that Python's approach to OOP may not be equivalent to Java et. al. Maybe list isn't actually a class - maybe it's just a function that returns an iterable when the tachyon beams are set to glorious and the unboxed hyper enumeration is quantized, but...I don't care. I just want to know how to sort lists. (Apologies for the angst - too much caffeine today)

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  • Code golf: combining multiple sorted lists into a single sorted list

    - by Alabaster Codify
    Implement an algorithm to merge an arbitrary number of sorted lists into one sorted list. The aim is to create the smallest working programme, in whatever language you like. For example: input: ((1, 4, 7), (2, 5, 8), (3, 6, 9)) output: (1, 2, 3, 4, 5, 6, 7, 8, 9) input: ((1, 10), (), (2, 5, 6, 7)) output: (1, 2, 5, 6, 7, 10) Note: solutions which concatenate the input lists then use a language-provided sort function are not in-keeping with the spirit of golf, and will not be accepted: sorted(sum(lists,[])) # cheating: out of bounds! Apart from anything else, your algorithm should be (but doesn't have to be) a lot faster! Clearly state the language, any foibles and the character count. Only include meaningful characters in the count, but feel free to add whitespace to the code for artistic / readability purposes. To keep things tidy, suggest improvement in comments or by editing answers where appropriate, rather than creating a new answer for each "revision". EDIT: if I was submitting this question again, I would expand on the "no language provided sort" rule to be "don't concatenate all the lists then sort the result". Existing entries which do concatenate-then-sort are actually very interesting and compact, so I won't retro-actively introduce a rule they break, but feel free to work to the more restrictive spec in new submissions. Inspired by http://stackoverflow.com/questions/464342/combining-two-sorted-lists-in-python

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  • Trouble with Router::url() when using named parameters

    - by sibidiba
    I'm generating plain simple links with CakePHP's HtmlHelper the following way: $html->link("Newest", array( 'controller' => 'posts', 'action' => 'listView', 'page'=> 1, 'sort'=>'Question.created', 'direction'=>'desc', )); Having the following route rule: Router::connect('/foobar/*',array( 'controller' => 'posts', 'action' => 'listView' )); The link is nicely generated as /foobar/page:1/sort:Question.created/direction:desc. Just as I want, it uses my URL prefix instead of controller/action names. However, for some links I must add named parameters like this: $html->link("Newest", array( 'controller' => 'posts', 'action' => 'listView', 'page'=> 1, 'sort'=>'Question.created', 'direction'=>'desc', 'namedParameter' => 'namedParameterValue' )); The link in this case points to /posts/listView/page:1/sort:Question.created/direction:desc/namedParameter:namedParameterValue. But I do not want to have contoller/action names in my URL-s, why is Cake ignoring in this case my routers configuration?

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  • PHP Function needed for GENERIC sorting of a recordset array

    - by donbriggs
    Somebody must have come up with a solution for this by now. I wrote a PHP class to display a recordset as an HTML table/datagrid, and I wish to expand it so that we can sort the datagrid by whichever column the user selects. In the below example data, we may need to sort the recordset array by Name, Shirt, Assign, or Age fields. I will take care of the display part, I just need help with sorting the data array. As usual, I query a database to get a result, iterate throught he result, and put the records into an assciateiave array. So, we end up with an array of arrays. (See below.) I need to be able to sort by any column in the dataset. However, I will not know the column names at design time, nor will I know if the colums will be string or numeric values. I have seen a ton of solutions to this, but I have not seen a GOOD and GENERIC solution Can somebody please suggest a way that I can sort the recordset array that is GENERIC, and will work on any recordset? Again, I will not know the fields names or datatypes at design time. The array presented below is ONLY an example. Array ( [0] = Array ( [name] = Kirk [shrit] = Gold [assign] = Bridge ) [1] => Array ( [name] => Spock [shrit] => Blue [assign] => Bridge ) [2] => Array ( [name] => Uhura [shrit] => Red [assign] => Bridge ) [3] => Array ( [name] => Scotty [shrit] => Red [assign] => Engineering ) [4] => Array ( [name] => McCoy [shrit] => Blue [assign] => Sick Bay ) )

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  • Data Structures for Junior Java Developer

    - by user1639637
    Ok,still learning Arrays. I wrote this code which fills the array named "rand" with random numbers between 0 and 1( exclusive). I want to start learning Complexity. the For loop executes n times (100 times) ,every time it takes O(1) time,so the worse case scenario is O(n),am I right? Also,I used ArrayList to store the 100 elements and I imported "Collections" and used Collections.sort() method to sort the elements. import java.util.Arrays; public class random { public static void main(String args[]) { double[] rand=new double[10]; for(int i=0;i<rand.length;i++) { rand[i]=(double) Math.random(); System.out.println(rand[i]); } Arrays.sort(rand); System.out.println(Arrays.toString(rand)); } } ArrayList: import java.util.ArrayList; import java.util.Collections; public class random { public static void main(String args[]) { ArrayList<Double> MyArrayList=new ArrayList<Double>(); for(int i=0;i<100;i++) { MyArrayList.add(Math.random()); } Collections.sort(MyArrayList); for(int j=0;j<MyArrayList.size();j++) { System.out.println(MyArrayList.get(j)); } } }

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  • Sorting in dataview not happening properly(C#3.0)

    - by Newbie
    I have the following DataTable dt = new DataTable(); dt.Columns.Add("col1", typeof(string)); dt.Columns.Add("col2", typeof(string)); dt.Rows.Add("1", "r1"); dt.Rows.Add("1", "r2"); dt.Rows.Add("1", "r3"); dt.Rows.Add("1", "r4"); dt.Rows.Add("2", "r1"); dt.Rows.Add("2", "r2"); dt.Rows.Add("2", "r3"); dt.Rows.Add("2", "r4"); dt.Rows.Add("3", "r1"); dt.Rows.Add("3", "r2"); dt.Rows.Add("3", "r3"); dt.Rows.Add("3", "r4"); dt.Rows.Add("1", "r1"); dt.Rows.Add("1", "r2"); DataView dv = new DataView(dt); dv.Sort = "col1"; DataTable dResult = dv.Table; I am trying to sort the datatable with the help of dataview so that the result will be 1 r1 1 r2 ... 2 r1 2 r2 ... 3 r1 3 r2 ...... Means all 1's first followed by 2's and 3r's Even I tried with dt.DefaultView.Sort = "col1"; but no luck. But it is not happening. Only the result i am able to view in dv.Sort and not the datatable (dResult) I am using C#3.0. Please help Thanks

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  • sorting a gridview alphabetically when columns are codes

    - by nat
    hi there i have a gridview populated by a Web Service search function. some of the columns in the grid are templatefields, because the values coming back from the search (in a datatable) are ids - i then use these ids to lookup the values when the rowdatabound event is triggered and populate a label or some such. this means that my sorting function for these id/lookup columns sorts by the ids rather than the textual value that i have looked up and actually populated the grid with (although i do put the ids in the grids datakeys). what i want to do is top be able to sort by the looked up textual value rather than the codes for these particular columns. what i was going to do to get around this was to when the datatable comes back from the search, adding more columns the textual values and doing all the looking up then, thus being able to sort directly from the manually added columns. is there another way to do this? as that approach seems like a bit of a bodge. although i guess it does remove having to do the looking up in the rowdatabound event.... my sorting function works by sticking the datatable in the session and on each bind grabbing the sort column and binding the gridview to a DataView with the sort attribute set to the column - and the direction. thanks nat

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  • .Net long-running scheduled code execution

    - by Prof Plum
    I am working on a couple of projects now where I really wish there was some sort of component that I could specify a time and date, and then execute some sort of method. DateTime date = new DateTime(x,x,x,x,x,x); ScheduledMethod sMethod = new ScheduledMethod(date, [method delegate of some sort]); \\at the specified date, sMethod invokes [method delegate of some sort] I know that I can do this with Windows Workflow Foundation as a long running process, which is good for certain things, but are there any alternatives? Workflow is not exactly straight forward with the details, and it would be nice to be able to deploy something more simple for light weight tasks. An example would be a method that checks a network folder once a day and deletes any files that are more than 30 days old. I realize that this may be pie in the sky dreaming, but this would be extremely useful for automating certain mundane maintinence tasks (scheduled sql operations, file system cleansing, routine email sending, etc.). It does not necessarily have to be .Net, but that is where I am coming from. Any ideas?

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  • How to populate Range variable from a Sub/Function call?

    - by Ken Ingram
    I am trying to get this sub to work but the operationalRange variable is not being assigned. Despite the fact that the function selectBodyRow(bodyName) works fine. Sub sortRows(bodyName As String, ByRef wksht As Worksheet) Dim operationalRange As Range Set operationalRange = selectBodyRow(bodyName) Debug.Print "Sorting Worksheet: " & wksht.Name If Not operationalRange Is Nothing Then operationalRange.Select Debug.Print "Sorting " & operationalRange.Count & "Rows." ActiveWorkbook.Worksheets(wksht.Name).Sort.SortFields.Clear ActiveWorkbook.Worksheets(wksht.Name).Sort.SortFields.Add Key:=operationalRange, _ SortOn:=xlSortOnValues, Order:=xlAscending, DataOption:=xlSortNormal ActiveWorkbook.Worksheets(wksht.Name).Sort.SortFields.Add Key:=operationalRange, _ SortOn:=xlSortOnValues, Order:=xlAscending, DataOption:=xlSortNormal With ActiveWorkbook.Worksheets(wksht.Name).Sort .SetRange operationalRange .Header = xlGuess .MatchCase = False .Orientation = xlTopToBottom .SortMethod = xlPinYin .Apply End With Else MsgBox "Body is not being Set" End If End Sub The Sub being called by the above Sub is: Function selectBodyRow(bodyName As String) As Range Dim rangeStart As String, rangeEnd As String Dim selectionStart As Range, selectionEnd As Range Dim result As Range, srchRng As Range, cngrs As Variant If bodyName = "WEST" Then rangeStart = "<-WEST START->" rangeEnd = "<-WEST END->" ElseIf bodyName = "EAST" Then rangeStart = "<-EAST START->" rangeEnd = "<-EAST END->" End If Set srchRng = Range("A:A") srchRng.Select Set selectionStart = srchRng.Find(What:=rangeStart, After:=ActiveCell, LookIn _ :=xlValues, LookAt:=xlPart, SearchOrder:=xlByRows, SearchDirection:= _ xlNext, MatchCase:=False, SearchFormat:=False) Set selectionEnd = srchRng.Find(What:=rangeEnd, After:=ActiveCell, LookIn _ :=xlValues, LookAt:=xlPart, SearchOrder:=xlByRows, SearchDirection:= _ xlNext, MatchCase:=False, SearchFormat:=False) Set result = Range(selectionStart.Offset(1, 0), selectionEnd.Offset(-1, 0)) result.EntireRow.Select End Function

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  • How do the operators < and > work with pointers?

    - by Øystein
    Just for fun, I had a std::list of const char*, each element pointing to a null-terminated text string, and ran a std::list::sort() on it. As it happens, it sort of (no pun intended) did not sort the strings. Considering that it was working on pointers, that makes sense. According to the documentation of std::list::sort(), it (by default) uses the operator < between the elements to compare. Forgetting about the list for a moment, my actual question is: How do these (, <, =, <=) operators work on pointers in C++ and C? Do they simply compare the actual memory addresses? char* p1 = (char*) 0xDAB0BC47; char* p2 = (char*) 0xBABEC475; e.g. on a 32-bit, little-endian system, p1 p2 because 0xDAB0BC47 0xBABEC475? Testing seems to confirm this, but I thought it'd be good to put it on StackOverflow for future reference. C and C++ both do some weird things to pointers, so you never really know...

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  • Unsort: remembering a permutation and undoing it.

    - by dreeves
    Suppose I have a function f that takes a vector v and returns a new vector with the elements transformed in some way. It does that by calling function g that assumes the vector is sorted. So I want f to be defined like so: f[v_] := Module[{s, r}, s = Sort[v]; (* remember the permutation applied in order to sort v *) r = g[s]; Unsort[r] (* apply the inverse of that permutation *) ] What's the best way to do the "Unsort"? Or could we get really fancy and have this somehow work: answer = Unsort[g[Sort[v]]]; ADDED: Let's make this concrete with a toy example. Suppose we want a function f that takes a vector and transforms it by adding to each element the next smallest element, if any. That's easy to write if we assume the vector is sorted, so let's write a helper function g that makes that assumption: g[v_] := v + Prepend[Most@v, 0] Now for the function we really want, f, that works whether or not v is sorted: f[v_] := (* remember the order; sort it; call g on it; put it back in the original order; return it *)

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  • nextgen gallery order issue

    - by mro
    Hi, wonder if anyone can help. I think what I'm after won't be solved by any exsiting code in nextgen plugin (in wordpress) due to the custom way I'm using it hence I come to stackoverflow for some opnions. Bascially - I am only really using the admin of nextgen to work with the gallerys etc. The actual meat of the functionality I'm querying the nextgen DB's direct from my code, I would have loved to use the inbuilt gallerys in nextgen, but my spec specifics were so custom I couldn't. My issue is, I need to pull the images from the DB's in the order it is in the admin (ie if a user pulls the sort order around in the drag and drop area). I have noticed however this doesn't affect the image id order in the DB, and wouldn't expect it to - that would be some complex shifting around just to reorder everytime surely. So obviously when I query the DB the order it's looking at is when it was created, by image id, with my filtering on top. I'm wondering though if there is a way I can query that sort order that's determined in the admin somehow, then at least I could sort the array somehow in the code ? does next gen store it's user custom sort order somewhere ? Hope this makes sense :) any thoughts appreciated. Thanks

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  • Why is a DataViewManager not sorting?

    - by Alarion
    First off, a quick rundown of what the code is doing. I have two tables: Companies and Clients. There is a one to many relationship between Companies and Clients (one company can have many clients). In some processing logic, I have both tables loaded into a DataSet - each are DataTables. I have added a DataRelation to set the relationship, and it works when I use GetChildRows on a record from the Companies table. However, I need to sort the records returned. After googling around some it looks like the DataViewManager is the way to go, and I have examined several basic examples. However, I cannot get my rows sorted. Am I missing something, or am I not using this how it is supposed to be used? Example code: Dim ldvmManager As New DataViewManager(mdsData) ldvmManager.DataViewSettings("Companies").Sort = "comName ASC" ldvmManager.DataViewSettings("Clients").ApplyDefaultSort = False ldvmManager.DataViewSettings("Clients").Sort = "entLastName ASC, entFirstName ASC" For Each mdrCurrentCompany in ldvmManager.DataViewSettings("Companies").Table.Rows Dim ldrClients() as DataRow = mdrCurrentCompany.GetChildRows("CompaniesClients") Next No matter what I do, the first Client returned has a last name that starts with a 'B' and the second has one that starts with a 'A'. From there, the order is all mixed up. If I use my entire data instead of the subset I was using to test with, the first Client returned has a last name that starts with 'J'. It seems like it is still using whatever default sort was being used before I tried to use the DataViewManager. Any ideas?

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  • Getting JQuery UI Sortable to work on asp.net ListView items?

    - by Xaisoft
    I have the following ListView in which I am using the JQuery UI sortable function to be able to sort the items in the ListView. The problem is that I can't put a sortable class on the table in the ItemTemplate because it does not work, if I put a class="sortable" on the outer div, it works, but it allows me to sort everything within the ListView, I just want to be able to move sort the tables. Here is the markup <div> //Works here, but hr's become sortable too. <asp:ListView ID="lvwDocuments" runat="server"> <LayoutTemplate> <h3> Documents</h3> <asp:PlaceHolder ID="itemPlaceHolder" runat="server"> </asp:PlaceHolder> </LayoutTemplate> <ItemTemplate> <table class="sortable"> //Does not work Here <tr> <td> <p class="title"> <a runat="server" href='<%#Eval("url") %>'> <%#Eval("title") %></a></p> <br /> <p> <%#Eval("description") %></p> </td> </tr> </table> </ItemTemplate> <ItemSeparatorTemplate> <hr /> </ItemSeparatorTemplate> </div> Also, How can I preserve the sort order even after the page is refreshed.

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  • Can I set NHibernate's default "OrderBy" to be "CreatedDate" not "Id"?

    - by Chris F
    This is an oddball question I figure. Can I get NHibernate to ask SQL to sort data by CreatedDate by default unless I set an OrderBy in my HQL or Criteria? I'm interested in knowing whether this sort can be accomplished at the DB level to avoid bringing in LINQ. The reason is that I use GUIDs for Ids and when I do something like this: Sheet sheet = sheetRepository.Get(_someGUID); IList<SheetLineItems> lineItems = sheet.LineItems; to fetch all of the lineItems, they come back in whatever arbitrary way that SQL sorts that fetch, which I figure is GUID. At some point I'll add ordinals to my line items, but for now, I just want to use CreatedDate as the sort criteria. I don't want to be forced to do: IList<SheetLineItem> lineItems = sheetLineItemRepository.GetAll(_sheetGUID); and then writing that method to sort by CreatedDate. I figure if everything is just sorted on CreatedDate by default, that would be fine, unless specifically requested otherwise.

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  • implementing interface

    - by 1ace1
    hello guys so i have this assignment that i need to implement interface to go over an ArrayList and sort it (ascending or descnding).I dont want "the" answer i just need some suggestions on my approach and why i get this error Exception in thread "main" java.lang.ClassCastException: Week7.Check cannot be cast to java.lang.Comparable at java.util.Arrays.mergeSort(Unknown Source) at java.util.Arrays.sort(Unknown Source) at java.util.Collections.sort(Unknown Source) at Week7.TestCheck.main(TestCheck.java:18) This is how i did it: comparable had one method called public int compairTo(Object o) public class Check implements comparable { private Integer checkNumber; public Check(Integer newCheckNumber) { setCheckNumber(newCheckNumber); } public String toString() { return getCheckNumber().toString(); } public void setCheckNumber(Integer checkNumber) { this.checkNumber = checkNumber; } public Integer getCheckNumber() { return checkNumber; } @Override public int compairTo(Object o) { Check compair = (Check)o; int result = 0; if (this.getCheckNumber() > compair.getCheckNumber()) result = 1; else if(this.getCheckNumber() < compair.getCheckNumber()) result = -1; return result; } } in my main i had this import java.util.ArrayList; import java.util.Collections; public class TestCheck { public static void main(String[] args) { ArrayList checkList = new ArrayList(); checkList.add(new Check(445)); checkList.add(new Check(101)); checkList.add(new Check(110)); checkList.add(new Check(553)); checkList.add(new Check(123)); Collections.sort(checkList); for (int i =0; i < checkList.size(); i++){ System.out.println(checkList.get(i)); } } }

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  • How to stream authenticated content with MediaPlayer on Android

    - by 102790073222983779908
    I've seen quite a few posts askign this question on SO but there doesn't seem to be a definitive answer (or at least an answer I like!) I've got content protected behind basic auth (username/password) -- I can download it fine using the various HTTP download clases but for the life of me I can't sort out how to tell media player to stream it (and provide the authentication). I saw one post that suggested it wasn't possible since the MediaPlayer is all native code and doesn't things like the Authenticator. There are plenty of examples of how to first download to a cached copy and then play that back but....That sort of sucks (and the files maybe 100's of MB's). I saw at least one proposal to download it in smalish chunks and then start & stop the playback (redirecting to the new file) but that sort of sucks also since there would (I presume) be a stutter (I haven't tried it though) The best idea I have at this point is to start downloading to a cache file and then when it's 'full enough' start up playback while I continue to fill the file.... I hope that this works (but again, haven't tried it). Am I missing something obvious? It's so painful to have all the various pieces almost working and I sort of convinced myself that there had to be a way to natively stream protected content (or have it take a already established & qualified InputStream) but it appears no joy. BTW I'm a Mac/iPhone guy and a newb at Android so I'm still fighting a bit of Java learning.... Excuse me if I'm missing somthing obvious. -john

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  • Looking for something to add some standard rules for my c++ project.

    - by rkb
    Hello all, My team is developing a C++ project on linux. We use vim as editor. I want to enforce some code standard rules in our team in such a way that if the code is not in accordance with it, some sort of warning or error will be thrown when it builds or compiles. Not necessarily it builds but at least I can run some plugin or tools on that code to make sure it meets the standard. So that before committing to svn everyone need to run the code through some sort of plugin or script and make sure it meets the requirement and then only he/she can commit. Not sure if we can add some rules to vim, if there are any let me know about it. For eg. In our code standards all the member variables and private functions should start with _ class A{ private: int _count; float _amount; void _increment_count(){ ++_count; } } So I want to throw some warning or error or some sort of messages for this class if the variables are declared as follows. class A{ private: int count; float amount; void increment_count(){ ++_count; } } Please note that warning and error are not from compiler becoz program is still valid. Its from the tool I want to use so that code goes to re-factoring but still works fine on the executable side. I am looking for some sort of plugin or pre parsers or scripts which will help me in achieving all this. Currently we use svn; just to anser the comment.

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  • Sorting a table based on which header cell was clicked

    - by cf_PhillipSenn
    If I have the following: <table> <thead> <tr> <th><a href="Index.cfm?Sort=0">First</a></th> <th><a href="Index.cfm?Sort=1">Second</a></th> <th><a href="Index.cfm?Sort=2">Third</a></th> </tr> </thead> <tbody> <tr> <td>A</td> <td class="num">123</td> <td>XYZ</td> </tr> </tbody> </table> Q: How do I sort the table body based upon which table header cell was clicked? <script> $('th a').click(function() { var $this = $(this).closest('th'); console.log($this.index()); return false; }); </script> (I made each of the table header cells hyperlinks so that if the user has JavaScript turned off, it will follow the link and be sorted on the server side).

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  • The blocking nature of aggregates

    - by Rob Farley
    I wrote a post recently about how query tuning isn’t just about how quickly the query runs – that if you have something (such as SSIS) that is consuming your data (and probably introducing a bottleneck), then it might be more important to have a query which focuses on getting the first bit of data out. You can read that post here.  In particular, we looked at two operators that could be used to ensure that a query returns only Distinct rows. and The Sort operator pulls in all the data, sorts it (discarding duplicates), and then pushes out the remaining rows. The Hash Match operator performs a Hashing function on each row as it comes in, and then looks to see if it’s created a Hash it’s seen before. If not, it pushes the row out. The Sort method is quicker, but has to wait until it’s gathered all the data before it can do the sort, and therefore blocks the data flow. But that was my last post. This one’s a bit different. This post is going to look at how Aggregate functions work, which ties nicely into this month’s T-SQL Tuesday. I’ve frequently explained about the fact that DISTINCT and GROUP BY are essentially the same function, although DISTINCT is the poorer cousin because you have less control over it, and you can’t apply aggregate functions. Just like the operators used for Distinct, there are different flavours of Aggregate operators – coming in blocking and non-blocking varieties. The example I like to use to explain this is a pile of playing cards. If I’m handed a pile of cards and asked to count how many cards there are in each suit, it’s going to help if the cards are already ordered. Suppose I’m playing a game of Bridge, I can easily glance at my hand and count how many there are in each suit, because I keep the pile of cards in order. Moving from left to right, I could tell you I have four Hearts in my hand, even before I’ve got to the end. By telling you that I have four Hearts as soon as I know, I demonstrate the principle of a non-blocking operation. This is known as a Stream Aggregate operation. It requires input which is sorted by whichever columns the grouping is on, and it will release a row as soon as the group changes – when I encounter a Spade, I know I don’t have any more Hearts in my hand. Alternatively, if the pile of cards are not sorted, I won’t know how many Hearts I have until I’ve looked through all the cards. In fact, to count them, I basically need to put them into little piles, and when I’ve finished making all those piles, I can count how many there are in each. Because I don’t know any of the final numbers until I’ve seen all the cards, this is blocking. This performs the aggregate function using a Hash Match. Observant readers will remember this from my Distinct example. You might remember that my earlier Hash Match operation – used for Distinct Flow – wasn’t blocking. But this one is. They’re essentially doing a similar operation, applying a Hash function to some data and seeing if the set of values have been seen before, but before, it needs more information than the mere existence of a new set of values, it needs to consider how many of them there are. A lot is dependent here on whether the data coming out of the source is sorted or not, and this is largely determined by the indexes that are being used. If you look in the Properties of an Index Scan, you’ll be able to see whether the order of the data is required by the plan. A property called Ordered will demonstrate this. In this particular example, the second plan is significantly faster, but is dependent on having ordered data. In fact, if I force a Stream Aggregate on unordered data (which I’m doing by telling it to use a different index), a Sort operation is needed, which makes my plan a lot slower. This is all very straight-forward stuff, and information that most people are fully aware of. I’m sure you’ve all read my good friend Paul White (@sql_kiwi)’s post on how the Query Optimizer chooses which type of aggregate function to apply. But let’s take a look at SQL Server Integration Services. SSIS gives us a Aggregate transformation for use in Data Flow Tasks, but it’s described as Blocking. The definitive article on Performance Tuning SSIS uses Sort and Aggregate as examples of Blocking Transformations. I’ve just shown you that Aggregate operations used by the Query Optimizer are not always blocking, but that the SSIS Aggregate component is an example of a blocking transformation. But is it always the case? After all, there are plenty of SSIS Performance Tuning talks out there that describe the value of sorted data in Data Flow Tasks, describing the IsSorted property that can be set through the Advanced Editor of your Source component. And so I set about testing the Aggregate transformation in SSIS, to prove for sure whether providing Sorted data would let the Aggregate transform behave like a Stream Aggregate. (Of course, I knew the answer already, but it helps to be able to demonstrate these things). A query that will produce a million rows in order was in order. Let me rephrase. I used a query which produced the numbers from 1 to 1000000, in a single field, ordered. The IsSorted flag was set on the source output, with the only column as SortKey 1. Performing an Aggregate function over this (counting the number of rows per distinct number) should produce an additional column with 1 in it. If this were being done in T-SQL, the ordered data would allow a Stream Aggregate to be used. In fact, if the Query Optimizer saw that the field had a Unique Index on it, it would be able to skip the Aggregate function completely, and just insert the value 1. This is a shortcut I wouldn’t be expecting from SSIS, but certainly the Stream behaviour would be nice. Unfortunately, it’s not the case. As you can see from the screenshots above, the data is pouring into the Aggregate function, and not being released until all million rows have been seen. It’s not doing a Stream Aggregate at all. This is expected behaviour. (I put that in bold, because I want you to realise this.) An SSIS transformation is a piece of code that runs. It’s a physical operation. When you write T-SQL and ask for an aggregation to be done, it’s a logical operation. The physical operation is either a Stream Aggregate or a Hash Match. In SSIS, you’re telling the system that you want a generic Aggregation, that will have to work with whatever data is passed in. I’m not saying that it wouldn’t be possible to make a sometimes-blocking aggregation component in SSIS. A Custom Component could be created which could detect whether the SortKeys columns of the input matched the Grouping columns of the Aggregation, and either call the blocking code or the non-blocking code as appropriate. One day I’ll make one of those, and publish it on my blog. I’ve done it before with a Script Component, but as Script components are single-use, I was able to handle the data knowing everything about my data flow already. As per my previous post – there are a lot of aspects in which tuning SSIS and tuning execution plans use similar concepts. In both situations, it really helps to have a feel for what’s going on behind the scenes. Considering whether an operation is blocking or not is extremely relevant to performance, and that it’s not always obvious from the surface. In a future post, I’ll show the impact of blocking v non-blocking and synchronous v asynchronous components in SSIS, using some of LobsterPot’s Script Components and Custom Components as examples. When I get that sorted, I’ll make a Stream Aggregate component available for download.

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  • The blocking nature of aggregates

    - by Rob Farley
    I wrote a post recently about how query tuning isn’t just about how quickly the query runs – that if you have something (such as SSIS) that is consuming your data (and probably introducing a bottleneck), then it might be more important to have a query which focuses on getting the first bit of data out. You can read that post here.  In particular, we looked at two operators that could be used to ensure that a query returns only Distinct rows. and The Sort operator pulls in all the data, sorts it (discarding duplicates), and then pushes out the remaining rows. The Hash Match operator performs a Hashing function on each row as it comes in, and then looks to see if it’s created a Hash it’s seen before. If not, it pushes the row out. The Sort method is quicker, but has to wait until it’s gathered all the data before it can do the sort, and therefore blocks the data flow. But that was my last post. This one’s a bit different. This post is going to look at how Aggregate functions work, which ties nicely into this month’s T-SQL Tuesday. I’ve frequently explained about the fact that DISTINCT and GROUP BY are essentially the same function, although DISTINCT is the poorer cousin because you have less control over it, and you can’t apply aggregate functions. Just like the operators used for Distinct, there are different flavours of Aggregate operators – coming in blocking and non-blocking varieties. The example I like to use to explain this is a pile of playing cards. If I’m handed a pile of cards and asked to count how many cards there are in each suit, it’s going to help if the cards are already ordered. Suppose I’m playing a game of Bridge, I can easily glance at my hand and count how many there are in each suit, because I keep the pile of cards in order. Moving from left to right, I could tell you I have four Hearts in my hand, even before I’ve got to the end. By telling you that I have four Hearts as soon as I know, I demonstrate the principle of a non-blocking operation. This is known as a Stream Aggregate operation. It requires input which is sorted by whichever columns the grouping is on, and it will release a row as soon as the group changes – when I encounter a Spade, I know I don’t have any more Hearts in my hand. Alternatively, if the pile of cards are not sorted, I won’t know how many Hearts I have until I’ve looked through all the cards. In fact, to count them, I basically need to put them into little piles, and when I’ve finished making all those piles, I can count how many there are in each. Because I don’t know any of the final numbers until I’ve seen all the cards, this is blocking. This performs the aggregate function using a Hash Match. Observant readers will remember this from my Distinct example. You might remember that my earlier Hash Match operation – used for Distinct Flow – wasn’t blocking. But this one is. They’re essentially doing a similar operation, applying a Hash function to some data and seeing if the set of values have been seen before, but before, it needs more information than the mere existence of a new set of values, it needs to consider how many of them there are. A lot is dependent here on whether the data coming out of the source is sorted or not, and this is largely determined by the indexes that are being used. If you look in the Properties of an Index Scan, you’ll be able to see whether the order of the data is required by the plan. A property called Ordered will demonstrate this. In this particular example, the second plan is significantly faster, but is dependent on having ordered data. In fact, if I force a Stream Aggregate on unordered data (which I’m doing by telling it to use a different index), a Sort operation is needed, which makes my plan a lot slower. This is all very straight-forward stuff, and information that most people are fully aware of. I’m sure you’ve all read my good friend Paul White (@sql_kiwi)’s post on how the Query Optimizer chooses which type of aggregate function to apply. But let’s take a look at SQL Server Integration Services. SSIS gives us a Aggregate transformation for use in Data Flow Tasks, but it’s described as Blocking. The definitive article on Performance Tuning SSIS uses Sort and Aggregate as examples of Blocking Transformations. I’ve just shown you that Aggregate operations used by the Query Optimizer are not always blocking, but that the SSIS Aggregate component is an example of a blocking transformation. But is it always the case? After all, there are plenty of SSIS Performance Tuning talks out there that describe the value of sorted data in Data Flow Tasks, describing the IsSorted property that can be set through the Advanced Editor of your Source component. And so I set about testing the Aggregate transformation in SSIS, to prove for sure whether providing Sorted data would let the Aggregate transform behave like a Stream Aggregate. (Of course, I knew the answer already, but it helps to be able to demonstrate these things). A query that will produce a million rows in order was in order. Let me rephrase. I used a query which produced the numbers from 1 to 1000000, in a single field, ordered. The IsSorted flag was set on the source output, with the only column as SortKey 1. Performing an Aggregate function over this (counting the number of rows per distinct number) should produce an additional column with 1 in it. If this were being done in T-SQL, the ordered data would allow a Stream Aggregate to be used. In fact, if the Query Optimizer saw that the field had a Unique Index on it, it would be able to skip the Aggregate function completely, and just insert the value 1. This is a shortcut I wouldn’t be expecting from SSIS, but certainly the Stream behaviour would be nice. Unfortunately, it’s not the case. As you can see from the screenshots above, the data is pouring into the Aggregate function, and not being released until all million rows have been seen. It’s not doing a Stream Aggregate at all. This is expected behaviour. (I put that in bold, because I want you to realise this.) An SSIS transformation is a piece of code that runs. It’s a physical operation. When you write T-SQL and ask for an aggregation to be done, it’s a logical operation. The physical operation is either a Stream Aggregate or a Hash Match. In SSIS, you’re telling the system that you want a generic Aggregation, that will have to work with whatever data is passed in. I’m not saying that it wouldn’t be possible to make a sometimes-blocking aggregation component in SSIS. A Custom Component could be created which could detect whether the SortKeys columns of the input matched the Grouping columns of the Aggregation, and either call the blocking code or the non-blocking code as appropriate. One day I’ll make one of those, and publish it on my blog. I’ve done it before with a Script Component, but as Script components are single-use, I was able to handle the data knowing everything about my data flow already. As per my previous post – there are a lot of aspects in which tuning SSIS and tuning execution plans use similar concepts. In both situations, it really helps to have a feel for what’s going on behind the scenes. Considering whether an operation is blocking or not is extremely relevant to performance, and that it’s not always obvious from the surface. In a future post, I’ll show the impact of blocking v non-blocking and synchronous v asynchronous components in SSIS, using some of LobsterPot’s Script Components and Custom Components as examples. When I get that sorted, I’ll make a Stream Aggregate component available for download.

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  • ?Oracle????SELECT????UNDO

    - by Liu Maclean(???)
    ????????Oracle?????(dirty read),?Oracle??????Asktom????????Oracle???????, ???undo??????????(before image)??????Consistent, ???????????????Oracle????????????? ????????? ??,??,Oracle?????????????RDBMS,???????????? ?????????2?????: _offline_rollback_segments or _corrupted_rollback_segments ?2?????????Oracle???????????ORA-600[4XXX]???????????????,???2??????Undo??Corruption????????????,?????2????????????????? ??????????????_offline_rollback_segments ? _corrupted_rollback_segments ?2?????: ???????(FORCE OPEN DATABASE) ????????????(consistent read & delayed block cleanout) ??????rollback segment??? ?????:???????Oracle????????,??????????2?????,?????????????!! _offline_rollback_segments ? _corrupted_rollback_segments ???????????: ??2???????Undo Segments(???/???)????????online ?UNDO$???????????OFFLINE??? ???instance??????????????????? ??????Undo Segments????????active transaction????????????dead??SMON???(????????SMON??(?):Recover Dead transaction) _OFFLINE_ROLLBACK_SEGMENTS(offline undo segment list)????(hidden parameter)?????: ???startup???open database???????_OFFLINE_ROLLBACK_SEGMENTS????Undo segments(???/???),?????undo segments????????alert.log???TRACE?????,???????startup?? ?????????????,?ITL?????undo segments?: ???undo segments?transaction table?????????????????? ???????????commit,?????CR??? ????undo segments????(???corrupted??,???missed??)???????????alert.log,??????? ?DML?????????????????????????????????CPU,????????????????????? _CORRUPTED_ROLLBACK_SEGMENTS(corrupted undo segment list)??????????: ?????startup?open database???_CORRUPTED_ROLLBACK_SEGMENTS????undo segments(???/???)???????? ???????_CORRUPTED_ROLLBACK_SEGMENTS???undo segments????????????commit,???undo segments???drop??? ??????????? ??????????????????,?????????????????? ??bootstrap???????????,?????????ORA-00704: bootstrap process failure??,???????????(???Oracle????:??ORA-00600:[4000] ORA-00704: bootstrap process failure????) ??????_CORRUPTED_ROLLBACK_SEGMENTS????????????????????,??????????????? Oracle???????TXChecker??????????? ???????2?????,??????????????_CORRUPTED_ROLLBACK_SEGMENTS?????SELECT????UNDO???????: SQL> alter system set event= '10513 trace name context forever, level 2' scope=spfile; System altered. SQL> alter system set "_in_memory_undo"=false scope=spfile; System altered. 10513 level 2 event????SMON ??rollback ??? dead transaction _in_memory_undo ?? in memory undo ?? SQL> startup force; ORACLE instance started. Total System Global Area 3140026368 bytes Fixed Size 2232472 bytes Variable Size 1795166056 bytes Database Buffers 1325400064 bytes Redo Buffers 17227776 bytes Database mounted. Database opened. session A: SQL> conn maclean/maclean Connected. SQL> create table maclean tablespace users as select 1 t1 from dual connect by level exec dbms_stats.gather_table_stats('','MACLEAN'); PL/SQL procedure successfully completed. SQL> set autotrace on; SQL> select sum(t1) from maclean; SUM(T1) ---------- 501 Execution Plan ---------------------------------------------------------- Plan hash value: 1679547536 ------------------------------------------------------------------------------ | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ------------------------------------------------------------------------------ | 0 | SELECT STATEMENT | | 1 | 3 | 3 (0)| 00:00:01 | | 1 | SORT AGGREGATE | | 1 | 3 | | | | 2 | TABLE ACCESS FULL| MACLEAN | 501 | 1503 | 3 (0)| 00:00:01 | ------------------------------------------------------------------------------ Statistics ---------------------------------------------------------- 1 recursive calls 0 db block gets 3 consistent gets 0 physical reads 0 redo size 515 bytes sent via SQL*Net to client 492 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 1 rows processe ???????????,????current block, ????????,consistent gets??3? SQL> update maclean set t1=0; 501 rows updated. SQL> alter system checkpoint; System altered. ??session A?commit; ???? session: SQL> conn maclean/maclean Connected. SQL> SQL> set autotrace on; SQL> select sum(t1) from maclean; SUM(T1) ---------- 501 Execution Plan ---------------------------------------------------------- Plan hash value: 1679547536 ------------------------------------------------------------------------------ | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ------------------------------------------------------------------------------ | 0 | SELECT STATEMENT | | 1 | 3 | 3 (0)| 00:00:01 | | 1 | SORT AGGREGATE | | 1 | 3 | | | | 2 | TABLE ACCESS FULL| MACLEAN | 501 | 1503 | 3 (0)| 00:00:01 | ------------------------------------------------------------------------------ Statistics ---------------------------------------------------------- 0 recursive calls 0 db block gets 505 consistent gets 0 physical reads 108 redo size 515 bytes sent via SQL*Net to client 492 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 1 rows processed ?????? ?????????undo??CR?,???consistent gets??? 505 [oracle@vrh8 ~]$ ps -ef|grep LOCAL=YES |grep -v grep oracle 5841 5839 0 09:17 ? 00:00:00 oracleG10R25 (DESCRIPTION=(LOCAL=YES)(ADDRESS=(PROTOCOL=beq))) [oracle@vrh8 ~]$ kill -9 5841 ??session A???Server Process????,???dead transaction ????smon?? select ktuxeusn, to_char(sysdate, 'DD-MON-YYYY HH24:MI:SS') "Time", ktuxesiz, ktuxesta from x$ktuxe where ktuxecfl = 'DEAD'; KTUXEUSN Time KTUXESIZ KTUXESTA ---------- -------------------- ---------- ---------------- 2 06-AUG-2012 09:20:45 7 ACTIVE ???1?active rollback segment SQL> conn maclean/maclean Connected. SQL> set autotrace on; SQL> select sum(t1) from maclean; SUM(T1) ---------- 501 Execution Plan ---------------------------------------------------------- Plan hash value: 1679547536 ------------------------------------------------------------------------------ | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ------------------------------------------------------------------------------ | 0 | SELECT STATEMENT | | 1 | 3 | 3 (0)| 00:00:01 | | 1 | SORT AGGREGATE | | 1 | 3 | | | | 2 | TABLE ACCESS FULL| MACLEAN | 501 | 1503 | 3 (0)| 00:00:01 | ------------------------------------------------------------------------------ Statistics ---------------------------------------------------------- 0 recursive calls 0 db block gets 411 consistent gets 0 physical reads 108 redo size 515 bytes sent via SQL*Net to client 492 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 1 rows processed ????? ????kill?? ???smon ??dead transaction , ???????????? ?????undo??????? ????active?rollback segment??? SQL> select segment_name from dba_rollback_segs where segment_id=2; SEGMENT_NAME ------------------------------ _SYSSMU2$ SQL> alter system set "_corrupted_rollback_segments"='_SYSSMU2$' scope=spfile; System altered. ? _corrupted_rollback_segments ?? ???2?rollback segment, ????????undo SQL> startup force; ORACLE instance started. Total System Global Area 3140026368 bytes Fixed Size 2232472 bytes Variable Size 1795166056 bytes Database Buffers 1325400064 bytes Redo Buffers 17227776 bytes Database mounted. Database opened. SQL> conn maclean/maclean Connected. SQL> set autotrace on; SQL> select sum(t1) from maclean; SUM(T1) ---------- 94 Execution Plan ---------------------------------------------------------- Plan hash value: 1679547536 ------------------------------------------------------------------------------ | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ------------------------------------------------------------------------------ | 0 | SELECT STATEMENT | | 1 | 3 | 3 (0)| 00:00:01 | | 1 | SORT AGGREGATE | | 1 | 3 | | | | 2 | TABLE ACCESS FULL| MACLEAN | 501 | 1503 | 3 (0)| 00:00:01 | ------------------------------------------------------------------------------ Statistics ---------------------------------------------------------- 228 recursive calls 0 db block gets 29 consistent gets 5 physical reads 116 redo size 514 bytes sent via SQL*Net to client 492 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 4 sorts (memory) 0 sorts (disk) 1 rows processed SQL> / SUM(T1) ---------- 94 Execution Plan ---------------------------------------------------------- Plan hash value: 1679547536 ------------------------------------------------------------------------------ | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ------------------------------------------------------------------------------ | 0 | SELECT STATEMENT | | 1 | 3 | 3 (0)| 00:00:01 | | 1 | SORT AGGREGATE | | 1 | 3 | | | | 2 | TABLE ACCESS FULL| MACLEAN | 501 | 1503 | 3 (0)| 00:00:01 | ------------------------------------------------------------------------------ Statistics ---------------------------------------------------------- 0 recursive calls 0 db block gets 3 consistent gets 0 physical reads 0 redo size 514 bytes sent via SQL*Net to client 492 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 1 rows processed ?????? consistent gets???3,?????????????????,??ITL???UNDO SEGMENTS?_corrupted_rollback_segments????,???????????COMMIT??,????UNDO? ???????,?????????????????????????(????????????????????),????????????????? ???? , ?????

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  • Using an ATA-100 Hard Drive with a Thermaltake BlacX External Hard Drive Dock

    - by Joe
    Is it possible for a Thermaltake BlacX HDD Dock to connect to and recognize an ATA-100 Hard Drive? I know that the specifications for the BlacX say that it only supports SATA & SATAII, but I was hoping for one of three things: 1) for it to still work even though it isn't supported 2) for there to be some sort of workaround to make this possible 3) for there to be another part of some sort that I could purchase to make this work

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  • Most common account names used in ssh brute force attacks

    - by Charles Stewart
    Does anyone maintain lists of the most frequently guessed account names that are used by attackers brute-forcing ssh? For your amusement, from my main server's logs over the last month (43 313 failed ssh attempts), with root not getting as far as sshd: cas@txtproof:~$ grep -e sshd /var/log/auth* | awk ' { print $8 }' | sort | uniq -c | sort | tail -n 13 32 administrator 32 stephen 34 administration 34 sales 34 user 35 matt 35 postgres 38 mysql 42 oracle 44 guest 86 test 90 admin 16513 checking

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