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  • How to calculate this string-dissimilarity function efficiently?

    - by ybungalobill
    Hello, I was looking for a string metric that have the property that moving around large blocks in a string won't affect the distance so much. So "helloworld" is close to "worldhello". Obviously Levenshtein distance and Longest common subsequence don't fulfill this requirement. Using Jaccard distance on the set of n-grams gives good results but has other drawbacks (it's a pseudometric and higher n results in higher penalty for changing single character). [original research] As I thought about it, what I'm looking for is a function f(A,B) such that f(A,B)+1 equals the minimum number of blocks that one have to divide A into (A1 ... An), apply a permutation on the blocks and get B: f("hello", "hello") = 0 f("helloworld", "worldhello") = 1 // hello world -> world hello f("abba", "baba") = 2 // ab b a -> b ab a f("computer", "copmuter") = 3 // co m p uter -> co p m uter This can be extended for A and B that aren't necessarily permutations of each other: any additional character that can't be matched is considered as one additional block. f("computer", "combuter") = 3 // com uter -> com uter, unmatched: p and b. Observing that instead of counting blocks we can count the number of pairs of indices that are taken apart by a permutation, we can write f(A,B) formally as: f(A,B) = min { C(P) | P:|A|?|B|, P is bijective, ?i?dom(P) A[P(i)]=B[P(i)] } C(P) = |A| + |B| - |dom(P)| - |{ i | i,i+1?dom(P) and P(i)+1=P(i+1) }| - 1 The problem is... guess what... ... that I'm not able to calculate this in polynomial time. Can someone suggest a way to do this efficiently? Or perhaps point me to already known metric that exhibits similar properties?

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  • Trying to implement a method that can compare any two lists but it always returns false

    - by Tyler Pfaff
    Hello like the title says I'm trying to make a method that can compare any two lists for equality. I'm trying to compare them in a way that validates that every element of one list has the same value as every element of another list. My Equals method below always returns false, can anyone see why that is? Thank you! using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks; public class IEnumerableComparer<T> : IEqualityComparer<IEnumerable<T>> { public bool Equals(IEnumerable<T> x, IEnumerable<T> y) { for(int i = 0; i<x.Count();i++){ if(!Object.Equals(x.ElementAt(i), y.ElementAt(i))){ return false; } } return true; } public int GetHashCode(IEnumerable<T> obj) { if (obj == null) return 0; return unchecked(obj.Select(e => e.GetHashCode()).Aggregate(0, (a, b) => a + b)); } } Here is my data I'm using to test this Equals method. static void Main(string[] args) { Car car1 = new Car(); car1.make = "Toyota"; car1.model = "xB"; Car car2 = new Car(); car2.make = "Toyota"; car2.model = "xB"; List<Car> l1 = new List<Car>(); List<Car> l2 = new List<Car>(); l1.Add(car1); l2.Add(car2); IEnumerableComparer<Car> seq = new IEnumerableComparer<Car>(); bool b = seq.Equals(l1, l2); Console.Write(b); //always says false Console.Read(); } } Car class class Car { public String make { get; set; } public String model { get; set; } }

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  • Are bit operations quick?

    - by flashnik
    I'm dealing with a problem which needs to work with a lot of data. Currently its' values are represented as unsigned int. I know that real values do not exceed some limit, say 1000. That means that I can use unsigned short to store it. One profit is that it'll use less space. Do I have to pay for it by loosing in performance? Another assumption. I decided to store data as short but all calling functions use int, so I need to convert between these datatypes when storing/extracting values. Wiil the performance lost be dramatic? Third assumption. Due to great wish to econom memory I decided to use not short but just 10 bits packed into array of unsigned int. What will happen in this case comparing with previous ones?

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  • iPhone OS: making a switch statement that uses string literals as comparators instead of integers

    - by nickthedude
    So i'd like to do this: switch (keyPath) { case @"refreshCount": //do stuff case @"timesLaunched": //do other stuff } but apparently you can only use integers as the switch quantity. Is the only way to do this parse the string into an integer identifier and then run the switch statement? like this: nsinteger num = nil; if (keyPath isEqual:@"refreshCount") { num = 0 } if (keyPath isEqual:@"timesLaunched") { num = 1 } I'm trying to optimize this code to be as quick as possible because its going to get called quite often. thanks, Nick

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  • Any difference in compiler behavior for each of these snippets?

    - by HotHead
    Please consider following code: 1. uint16 a = 0x0001; if(a < 0x0002) { // do something } 2. uint16 a = 0x0001; if(a < uint16(0x0002)) { // do something } 3. uint16 a = 0x0001; if(a < static_cast<uint16>(0x0002)) { // do something } 4. uint16 a = 0x0001; uint16 b = 0x0002; if(a < b) { // do something } What compiler does in backgorund and what is the best (and correct) way to do above testing? p.s. sorry, but I couldn't find the better title :) EDIT: values 0x0001 and 0x0002 are only example. There coudl be any 2 byte value instead. Thank you in advance!

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  • STL find performs bettern than hand-crafter loop

    - by dusha
    Hello all, I have some question. Given the following C++ code fragment: #include <boost/progress.hpp> #include <vector> #include <algorithm> #include <numeric> #include <iostream> struct incrementor { incrementor() : curr_() {} unsigned int operator()() { return curr_++; } private: unsigned int curr_; }; template<class Vec> char const* value_found(Vec const& v, typename Vec::const_iterator i) { return i==v.end() ? "no" : "yes"; } template<class Vec> typename Vec::const_iterator find1(Vec const& v, typename Vec::value_type val) { return find(v.begin(), v.end(), val); } template<class Vec> typename Vec::const_iterator find2(Vec const& v, typename Vec::value_type val) { for(typename Vec::const_iterator i=v.begin(), end=v.end(); i<end; ++i) if(*i==val) return i; return v.end(); } int main() { using namespace std; typedef vector<unsigned int>::const_iterator iter; vector<unsigned int> vec; vec.reserve(10000000); boost::progress_timer pt; generate_n(back_inserter(vec), vec.capacity(), incrementor()); //added this line, to avoid any doubts, that compiler is able to // guess the data is sorted random_shuffle(vec.begin(), vec.end()); cout << "value generation required: " << pt.elapsed() << endl; double d; pt.restart(); iter found=find1(vec, vec.capacity()); d=pt.elapsed(); cout << "first search required: " << d << endl; cout << "first search found value: " << value_found(vec, found)<< endl; pt.restart(); found=find2(vec, vec.capacity()); d=pt.elapsed(); cout << "second search required: " << d << endl; cout << "second search found value: " << value_found(vec, found)<< endl; return 0; } On my machine (Intel i7, Windows Vista) STL find (call via find1) runs about 10 times faster than the hand-crafted loop (call via find2). I first thought that Visual C++ performs some kind of vectorization (may be I am mistaken here), but as far as I can see assembly does not look the way it uses vectorization. Why is STL loop faster? Hand-crafted loop is identical to the loop from the STL-find body. I was asked to post program's output. Without shuffle: value generation required: 0.078 first search required: 0.008 first search found value: no second search required: 0.098 second search found value: no With shuffle (caching effects): value generation required: 1.454 first search required: 0.009 first search found value: no second search required: 0.044 second search found value: no Many thanks, dusha. P.S. I return the iterator and write out the result (found or not), because I would like to prevent compiler optimization, that it thinks the loop is not required at all. The searched value is obviously not in the vector.

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  • beneficial in terms of performance

    - by Usama Khalil
    Hi, is it better to declare Webservice class object instances as static as the .asmx webservice classes have only static methods. what i want is that i declare and instantiate webservice asmx class as static in aspx Page Behind Class. and on every event call on that page i could perform operation against webservice methods. is it beneficial in terms of performance? Thanks Usama

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  • Getting an exception when trying to use extension method with SortedDictionary... why?

    - by Polaris878
    I'm trying to place custom objects into a sorted dictionary... I am then trying to use an extension method (Max()) on this sorted dictionary. However, I'm getting the exception: "At least one object must implement IComparable". I don't understand why I'm getting that, as my custom object obviously implements IComparable. Here is my code: public class MyDate : IComparable<MyDate> { int IComparable<MyDate>.CompareTo(MyDate obj) { if (obj != null) { if (this.Value.Ticks < obj.Value.Ticks) { return 1; } else if (this.Value.Ticks == obj.Value.Ticks) { return 0; } else { return -1; } } } public MyDate(DateTime date) { this.Value = date; } public DateTime Value; } class Program { static void Main(string[] args) { SortedDictionary<MyDate, int> sd = new SortedDictionary<MyDate,int>(); sd.Add(new MyDate(new DateTime(1)), 1); sd.Add(new MyDate(new DateTime(2)), 2); Console.WriteLine(sd.Max().Value); // Throws exception!! } } What on earth am I doing wrong???

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  • Does Google Analytics have peformance overhead?

    - by Mohit Nanda
    To what extent does Google Analytics impact performance? I'm looking for the following: Benchmarks (including response times/pageload times et al) Links or results to similar benchmarks One (possible) method of testing Google Analytics (GA) on your site: Serve ga.js (the Google Analytics JavaScript file) from your own server. Update from Google Daily (test 1) and Weekly (test 2). I would be interested to see how this reduces the communication between the client webserver and the GA server. Has anyone conducted any of these tests? If so, can you provide your results? If not, does anyone have a better method for testing the performance hit (or lack thereof) for using GA?

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  • When to use Vanilla Javascript vs. jQuery?

    - by jondavidjohn
    I have noticed while monitoring/attempting to answer common jQuery questions, that there are certain practices using javascript, instead of jQuery, that actually enable you to write less and do ... well the same amount. And may also yield performance benefits. A specific example $(this) vs this Inside a click event referencing the clicked objects id jQuery $(this).attr("id"); Javascript this.id; Are there any other common practices like this? Where certain Javascript operations could be accomplished easier, without bringing jQuery into the mix. Or is this a rare case? (of a jQuery "shortcut" actually requiring more code) EDIT : While I appreciate the answers regarding jQuery vs. plain javascript performance, I am actually looking for much more quantitative answers. While using jQuery, instances where one would actually be better off (readability/compactness) to use plain javascript instead of using $(). In addition to the example I gave in my original question.

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  • Lack of ImageList in MenuStrip and performance issues

    - by Ivan
    MenuStrip doesn't support using ImageList images. What are performance issues of this? Are there chances of using too much GDI resources and slow-downs? How many items should be considered acceptable, after which one should implement custom control that draws images from ImageList?

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  • How do compare dates when one of those are in string format in android

    - by Raj
    I am very much new to android so need some good help with a code example. I am getting a date in form of string from a server in the following format 2012-08-17 00:00:00 I want to compare this string with current date to find the difference between the dates in the form of year, months and days... I tried playing around it in the following code Date currentDate = new Date(System.currentTimeMillis()); Log.v("@@@@@@@@@","Current Date: " + currentDate); Date passDate = new SimpleDateFormat().parse(passDateString); Log.v("@@@@@@@@@","Pass Date: " + passDate); dateDifference = passDate.compareTo(currentDate); but it returned with following exception 04-15 12:08:29.101: V/@@@@@@@@@(1161): Current Date: Sun Apr 15 12:08:29 GMT+01:00 2012 04-15 12:08:29.101: W/System.err(1161): java.text.ParseException: Unparseable date: 2012-08-17 00:00:00 04-15 12:08:29.111: W/System.err(1161): at java.text.DateFormat.parse(DateFormat.java:645) 04-15 12:08:29.111: W/System.err(1161): at org.apis.PassesListItemAdapter.getView(PassesListItemAdapter.java:77) 04-15 12:08:29.111: W/System.err(1161): at android.widget.AbsListView.obtainView(AbsListView.java:1315) 04-15 12:08:29.111: W/System.err(1161): at android.widget.ListView.makeAndAddView(ListView.java:1727) 04-15 12:08:29.111: W/System.err(1161): at android.widget.ListView.fillDown(ListView.java:652) 04-15 12:08:29.111: W/System.err(1161): at android.widget.ListView.fillFromTop(ListView.java:709) 04-15 12:08:29.111: W/System.err(1161): at android.widget.ListView.layoutChildren(ListView.java:1580) 04-15 12:08:29.111: W/System.err(1161): at android.widget.AbsListView.onLayout(AbsListView.java:1147) 04-15 12:08:29.111: W/System.err(1161): at android.view.View.layout(View.java:7034) 04-15 12:08:29.111: W/System.err(1161): at android.widget.RelativeLayout.onLayout(RelativeLayout.java:909) 04-15 12:08:29.111: W/System.err(1161): at android.view.View.layout(View.java:7034) 04-15 12:08:29.111: W/System.err(1161): at android.widget.FrameLayout.onLayout(FrameLayout.java:333) 04-15 12:08:29.111: W/System.err(1161): at android.view.View.layout(View.java:7034) 04-15 12:08:29.111: W/System.err(1161): at android.widget.FrameLayout.onLayout(FrameLayout.java:333) 04-15 12:08:29.111: W/System.err(1161): at android.view.View.layout(View.java:7034) 04-15 12:08:29.111: W/System.err(1161): at android.view.ViewRoot.performTraversals(ViewRoot.java:1049) 04-15 12:08:29.111: W/System.err(1161): at android.view.ViewRoot.handleMessage(ViewRoot.java:1744) 04-15 12:08:29.111: W/System.err(1161): at android.os.Handler.dispatchMessage(Handler.java:99) 04-15 12:08:29.111: W/System.err(1161): at android.os.Looper.loop(Looper.java:144) 04-15 12:08:29.111: W/System.err(1161): at android.app.ActivityThread.main(ActivityThread.java:4937) 04-15 12:08:29.111: W/System.err(1161): at java.lang.reflect.Method.invokeNative(Native Method) 04-15 12:08:29.111: W/System.err(1161): at java.lang.reflect.Method.invoke(Method.java:521) 04-15 12:08:29.111: W/System.err(1161): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868) 04-15 12:08:29.111: W/System.err(1161): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626) 04-15 12:08:29.111: W/System.err(1161): at dalvik.system.NativeStart.main(Native Method) I am stuck... please help Raj

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  • Why would Linux VM in vSphere ESXi 5.5 show dramatically increased disk i/o latency?

    - by mhucka
    I'm stumped and I hope someone else will recognize the symptoms of this problem. Hardware: new Dell T110 II, dual-core Pentium G860 2.9 GHz, onboard SATA controller, one new 500 GB 7200 RPM cabled hard drive inside the box, other drives inside but not mounted yet. No RAID. Software: fresh CentOS 6.5 virtual machine under VMware ESXi 5.5.0 (build 174 + vSphere Client). 2.5 GB RAM allocated. The disk is how CentOS offered to set it up, namely as a volume inside an LVM Volume Group, except that I skipped having a separate /home and simply have / and /boot. CentOS is patched up, ESXi patched up, latest VMware tools installed in the VM. No users on the system, no services running, no files on the disk but the OS installation. I'm interacting with the VM via the VM virtual console in vSphere Client. Before going further, I wanted to check that I configured things more or less reasonably. I ran the following command as root in a shell on the VM: for i in 1 2 3 4 5 6 7 8 9 10; do dd if=/dev/zero of=/test.img bs=8k count=256k conv=fdatasync done I.e., just repeat the dd command 10 times, which results in printing the transfer rate each time. The results are disturbing. It starts off well: 262144+0 records in 262144+0 records out 2147483648 bytes (2.1 GB) copied, 20.451 s, 105 MB/s 262144+0 records in 262144+0 records out 2147483648 bytes (2.1 GB) copied, 20.4202 s, 105 MB/s ... but after 7-8 of these, it then prints 262144+0 records in 262144+0 records out 2147483648 bytes (2.1 GG) copied, 82.9779 s, 25.9 MB/s 262144+0 records in 262144+0 records out 2147483648 bytes (2.1 GB) copied, 84.0396 s, 25.6 MB/s 262144+0 records in 262144+0 records out 2147483648 bytes (2.1 GB) copied, 103.42 s, 20.8 MB/s If I wait a significant amount of time, say 30-45 minutes, and run it again, it again goes back to 105 MB/s, and after several rounds (sometimes a few, sometimes 10+), it drops to ~20-25 MB/s again. Plotting the disk latency in vSphere's interface, it shows periods of high disk latency hitting 1.2-1.5 seconds during the times that dd reports the low throughput. (And yes, things get pretty unresponsive while that's happening.) What could be causing this? I'm comfortable that it is not due to the disk failing, because I also had configured two other disks as an additional volume in the same system. At first I thought I did something wrong with that volume, but after commenting the volume out from /etc/fstab and rebooting, and trying the tests on / as shown above, it became clear that the problem is elsewhere. It is probably an ESXi configuration problem, but I'm not very experienced with ESXi. It's probably something stupid, but after trying to figure this out for many hours over multiple days, I can't find the problem, so I hope someone can point me in the right direction. (P.S.: yes, I know this hardware combo won't win any speed awards as a server, and I have reasons for using this low-end hardware and running a single VM, but I think that's besides the point for this question [unless it's actually a hardware problem].) ADDENDUM #1: Reading other answers such as this one made me try adding oflag=direct to dd. However, it makes no difference in the pattern of results: initially the numbers are higher for many rounds, then they drop to 20-25 MB/s. (The initial absolute numbers are in the 50 MB/s range.) ADDENDUM #2: Adding sync ; echo 3 > /proc/sys/vm/drop_caches into the loop does not make a difference at all. ADDENDUM #3: To take out further variables, I now run dd such that the file it creates is larger than the amount of RAM on the system. The new command is dd if=/dev/zero of=/test.img bs=16k count=256k conv=fdatasync oflag=direct. Initial throughput numbers with this version of the command are ~50 MB/s. They drop to 20-25 MB/s when things go south. ADDENDUM #4: Here is the output of iostat -d -m -x 1 running in another terminal window while performance is "good" and then again when it's "bad". (While this is going on, I'm running dd if=/dev/zero of=/test.img bs=16k count=256k conv=fdatasync oflag=direct.) First, when things are "good", it shows this: When things go "bad", iostat -d -m -x 1 shows this:

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  • How a JIT compiler helps performance of applications?

    - by igorgue
    I just read that Android has a 450% performance improvement because it added a JIT compiler, I know what JIT is, but I don't really understand why is it faster than normal compiled code? or what's the difference with the older approach from the Android platform (the Java like run compiled bytecode). Thanks!

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  • How to compare two floating-point values in shell script

    - by Reem
    I had to do a division in shell script and the best way was: result1=`echo "scale=3; ($var1 / $total) * 100"| bc -l` result2=`echo "scale=3; ($var2 / $total) * 100"| bc -l` but I want to compare the values of $result1 and $result2 Using if test $result1 -lt $result2 or if [ $result1 -gt $result2 ] didn't work :( Any idea how to do that?

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  • Algorithm to find a measurement of similarity between lists.

    - by Cubed
    Given that I have two lists that each contain a separate subset of a common superset, is there an algorithm to give me a similarity measurement? Example: A = { John, Mary, Kate, Peter } and B = { Peter, James, Mary, Kate } How similar are these two lists? Note that I do not know all elements of the common superset. Update: I was unclear and I have probably used the word 'set' in a sloppy fashion. My apologies. Clarification: Order is of importance. If identical elements occupy the same position in the list, we have the highest similarity for that element. The similarity decreased the farther apart the identical elements are. The similarity is even lower if the element only exists in one of the lists. I could even add the extra dimension that lower indices are of greater value, so a a[1] == b[1] is worth more than a[9] == b[9], but that is mainly cause I am curious.

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  • How to compare two "not integer" values in shell script

    - by Reem
    I had to do a division in shell script and the best way was: result1=`echo "scale=3; ($var1 / $total) * 100"| bc -l` result2=`echo "scale=3; ($var2 / $total) * 100"| bc -l` but I want to compare the values of $result1 and $result2 Using if test $result1 -lt $result2 or if [ $result1 -gt $result2 ] didn't work :( Any idea how to do that?

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  • Choking experienced while using the TCP/IP Adapter for BizTalk Server 2006

    - by Burhan
    I am using the TCP/IP Adapter for BizTalk Server 2006 which was obtained from codeplex: http://www.codeplex.com/BTSTCPIP Once the application was deployed in production, we started to experience choking in the performance of the application. The more the requests, the more the performance degradation. Sometimes, it happens that the receive ports become non-responsive and we have to forcefully restart the host instances to temporarily let the services respond again but we experience the same problems again and again. I would like to ask if any of you have used the same adapter and have you ever experienced the similar issues? If yes, how can we overcome theses issues. Thanks.

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  • In C, would !~b ever be faster than b == 0xff ?

    - by James Morris
    From a long time ago I have a memory which has stuck with me that says comparisons against zero are faster than any other value (ahem Z80). In some C code I'm writing I want to skip values which have all their bits set. Currently the type of these values is char but may change. I have two different alternatives to perform the test: if (!~b) /* skip */ and if (b == 0xff) /* skip */ Apart from the latter making the assumption that b is an 8bit char whereas the former does not, would the former ever be faster due to the old compare to zero optimization trick, or are the CPUs of today way beyond this kind of thing?

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  • Why is Decimal('0') > 9999.0 True in Python?

    - by parxier
    This is somehow related to my question Why is ''0 True in Python? In Python 2.6.4: >> Decimal('0') > 9999.0 True From the answer to my original question I understand that when comparing objects of different types in Python 2.x the types are ordered by their name. But in this case: >> type(Decimal('0')).__name__ > type(9999.0).__name__ False Why is Decimal('0') > 9999.0 == True then? UPDATE: I usually work on Ubuntu (Linux 2.6.31-20-generic #57-Ubuntu SMP Mon Feb 8 09:05:19 UTC 2010 i686 GNU/Linux, Python 2.6.4 (r264:75706, Dec 7 2009, 18:45:15) [GCC 4.4.1] on linux2). On Windows (WinXP Professional SP3, Python 2.6.4 (r264:75706, Nov 3 2009, 13:23:17) [MSC v.1500 32 bit (Intel)] on win32) my original statement works differently: >> Decimal('0') > 9999.0 False I even more puzzled now. %-(

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  • SQL Server architecture guidance

    - by Liam
    Hi, We are designing a new version of our existing product on a new schema. Its an internal web application with possibly 100 concurrent users (max)This will run on a SQL Server 2008 database. On of the discussion items recently is whether we should have a single database of split the database for performance reasons across 2 separate databases. The database could grow anywhere from 50-100GB over 5 years. We are Developers and not DBAs so it would be nice to get some general guidance. [I know the answer is not simple as it depends on the schema, archiving policy, amount of data etc. ] Option 1 Single Main Database [This is my preferred option]. The plan would be to have all the tables in a single database and possibly to use file groups and partitioning to separate the data if required across multiple disks. [Use schema if appropriate]. This should deal with the performance concerns One of the comments wrt this was that the a single server instance would still be processing this data so there would still be a processing bottle neck. For reporting we could have a separate reporting DB but this is still being discussed. Option 2 Split the database into 2 separate databases DB1 - Customers, Accounts, Customer resources etc DB2 - This would contain the bulk of the data [i.e. Vehicle tracking data, financial transaction tables etc]. These tables would typically contain a lot of data. [It could reside on a separate server if required] This plan would involve keeping the main data in a smaller database [DB1] and retaining the [mainly] read only transaction type data in a separate DB [DB2]. The UI would mainly read from DB1 and thus be more responsive. [I'm aware that this option makes it harder for Referential Integrity to be enforced.] Points for consideration As we are at the design stage we can at least make proper use of indexes to deal performance issues so thats why option 1 to me is attractive and its more of a standard approach. For both options we are considering implementing an archiving database. Apologies for the long Question. In summary the question is 1 DB or 2? Thanks in advance, Liam

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