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  • What is microbenchmarking?

    - by polygenelubricants
    I've heard this term used, but I'm not entirely sure what it means, so: What DOES it mean and what DOESN'T it mean? What are some examples of what IS and ISN'T microbenchmarking? What are the dangers of microbenchmarking and how do you avoid it? (or is it a good thing?)

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  • Calling a method on an object a bunch of times versus constructing an object a bunch of times

    - by Ami
    I have a List called myData and I want to apply a particular method (someFunction) to every element in the List. Is calling a method through an object's constructor slower than calling the same method many times for one particular object instantiation? In other words, is this: for(int i = 0; i < myData.Count; i++) myClass someObject = new myClass(myData[i]); slower than this: myClass someObject = new myClass(); for(int i = 0; i < myData.Count; i++) someObject.someFunction(myData[i]); ? If so, how much slower?

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  • Why does the order of the loops affect performance when iterating over a 2D array? [closed]

    - by Mark
    Possible Duplicate: Which of these two for loops is more efficient in terms of time and cache performance Below are two programs that are almost identical except that I switched the i and j variables around. They both run in different amounts of time. Could someone explain why this happens? Version 1 #include <stdio.h> #include <stdlib.h> main () { int i,j; static int x[4000][4000]; for (i = 0; i < 4000; i++) { for (j = 0; j < 4000; j++) { x[j][i] = i + j; } } } Version 2 #include <stdio.h> #include <stdlib.h> main () { int i,j; static int x[4000][4000]; for (j = 0; j < 4000; j++) { for (i = 0; i < 4000; i++) { x[j][i] = i + j; } } }

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  • Storing information in the DOM?

    - by John
    Im making a small private message application in the form of a phone. Ten messages are shown at the time. And the list of messages are scrolled up/down by hiding them. Just how bad is it to use the DOM to store information in this way. My main goal for doing this is to reduce calls to the database. And instead of making a new call all the time, it only checks if any new messages has arrived and ads the new message(s). Whats the alternative, cookies anyone? Thank you for the time

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  • What to prefer in the following case?

    - by GK
    say suppose I have class as : public class Age { private int age; public int getAge() { return this.age; } } In my Main class I am calling the getAge() method many times. So I wanted to know is it advisable to call so many times or call once and assign it to some variable and use that variable. Which is best and why?

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  • MySQL TEXT field performance

    - by Jonathon
    I have several TEXT and/or MEDIUMTEXT fields in each of our 1000 MySQL tables. I now know that TEXT fields are written to disk rather than in memory when queried. Is that also true even if that field is not called in the query? For example, if I have a table (tbExam) with 2 fields (id int(11) and comment text) and I run SELECT id FROM tbExam, does MySQL still have to write that to disk before returning results or will it run that query in memory? I am trying to figure out if I need to reconfigure our actual db tables to switch to varchar(xxxx) or keep the text fields and reconfigure the queries.

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  • Reflector error or optimisation?

    - by David_001
    Long story short: I used reflector on the System.Security.Util.Tokenizer class, and there's loads of goto statements in there. Here's a brief example snippet: Label_0026: if (this._inSavedCharacter != -1) { num = this._inSavedCharacter; this._inSavedCharacter = -1; } else { switch (this._inTokenSource) { case TokenSource.UnicodeByteArray: if ((this._inIndex + 1) < this._inSize) { break; } stream.AddToken(-1); return; case TokenSource.UTF8ByteArray: if (this._inIndex < this._inSize) { goto Label_00CF; } stream.AddToken(-1); return; case TokenSource.ASCIIByteArray: if (this._inIndex < this._inSize) { goto Label_023C; } stream.AddToken(-1); return; case TokenSource.CharArray: if (this._inIndex < this._inSize) { goto Label_0272; } stream.AddToken(-1); return; case TokenSource.String: if (this._inIndex < this._inSize) { goto Label_02A8; } stream.AddToken(-1); return; case TokenSource.NestedStrings: if (this._inNestedSize == 0) { goto Label_030D; } if (this._inNestedIndex >= this._inNestedSize) { goto Label_0306; } num = this._inNestedString[this._inNestedIndex++]; goto Label_0402; default: num = this._inTokenReader.Read(); if (num == -1) { stream.AddToken(-1); return; } goto Label_0402; } num = (this._inBytes[this._inIndex + 1] << 8) + this._inBytes[this._inIndex]; this._inIndex += 2; } goto Label_0402; Label_00CF: num = this._inBytes[this._inIndex++]; if ((num & 0x80) != 0) { switch (((num & 240) >> 4)) { case 8: case 9: case 10: case 11: throw new XmlSyntaxException(this.LineNo); case 12: case 13: num &= 0x1f; num3 = 2; break; case 14: num &= 15; num3 = 3; break; case 15: throw new XmlSyntaxException(this.LineNo); } if (this._inIndex >= this._inSize) { throw new XmlSyntaxException(this.LineNo, Environment.GetResourceString("XMLSyntax_UnexpectedEndOfFile")); } byte num2 = this._inBytes[this._inIndex++]; if ((num2 & 0xc0) != 0x80) { throw new XmlSyntaxException(this.LineNo); } num = (num << 6) | (num2 & 0x3f); if (num3 != 2) { if (this._inIndex >= this._inSize) { throw new XmlSyntaxException(this.LineNo, Environment.GetResourceString("XMLSyntax_UnexpectedEndOfFile")); } num2 = this._inBytes[this._inIndex++]; if ((num2 & 0xc0) != 0x80) { throw new XmlSyntaxException(this.LineNo); } num = (num << 6) | (num2 & 0x3f); } } goto Label_0402; Label_023C: num = this._inBytes[this._inIndex++]; goto Label_0402; Label_0272: num = this._inChars[this._inIndex++]; goto Label_0402; Label_02A8: num = this._inString[this._inIndex++]; goto Label_0402; Label_0306: this._inNestedSize = 0; I essentially wanted to know how the class worked, but the number of goto's makes it impossible. Arguably something like a Tokenizer class needs to be heavily optimised, so my question is: is Reflector getting it wrong, or is goto an optimisation for this class?

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  • Java API Method Run Times

    - by Mike
    Is there a good resource to get run times for standard API functions? It's somewhat confusing when trying to optimize your program. I know Java isn't made to be particularly speedy but I can't seem to find much info on this at all. Example Problem: If I am looking for a certain token in a file is it faster to scan each line using string.contains(...) or to bring in say 100 or so lines putting them to a local string them performing contains on that chunk.

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  • Minimizing distance to a weighted grid

    - by Andrew Tomazos - Fathomling
    Lets suppose you have a 1000x1000 grid of positive integer weights W. We want to find the cell that minimizes the average weighted distance.to each cell. The brute force way to do this would be to loop over each candidate cell and calculate the distance: int best_x, best_y, best_dist; for x0 = 1:1000, for y0 = 1:1000, int total_dist = 0; for x1 = 1:1000, for y1 = 1:1000, total_dist += W[x1,y1] * sqrt((x0-x1)^2 + (y0-y1)^2); if (total_dist < best_dist) best_x = x0; best_y = y0; best_dist = total_dist; This takes ~10^12 operations, which is too long. Is there a way to do this in or near ~10^8 or so operations?

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  • Optimizing MySQL queries with IN operator

    - by Arkadiusz Kondas
    I have a MySQL database with a fairly large table where the products are. Each of them has its own id and categoryId field where there is a category id belongs to this product. Now I have a query that pulls out products from given categories such as: SELECT * FROM products WHERE categoryId IN ( 1, 2, 3, 4, 5, 34, 6, 7, 8, 9, 10, 11, 12 ) Of course, come a WHERE clause and ORDER BY sort but not in this thing. Let's say that these products is 250k and the visits are over 100k per day. Under such conditions in the table slow_log registered weight of these queries with large generation time. Do you have any ideas how to optimize the given problem? Table engine is MyISAM.

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  • which one is a faster/better sql practice?

    - by artsince
    Suppose I have a 2 column table (id, flag) and id is sequential. I expect this table to contain a lot of records. I want to periodically select the first row not flagged and update it. Some of the records on the way may have already been flagged, so I want to skip them. Does it make more sense if I store the last id I flagged and use it in my select statement, like select * from mytable where id > my_last_id order by id asc limit 1 or simply get the first unflagged row, like: select * from mytable where flagged = 'F' order by id asc limit 1 Thank you!

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  • Is it faster to compute values in a query, call a Scalar Function (decimal(28,2) datatype) 4 times,

    - by Pulsehead
    I have a handful of queries I need to write in SQL Server 2005. Each Query will be calculating 4 unit cost values based on a handful of (up to 11) fields. Any time I want 1 of these 4 unit cost values, I'll want all 4. Which is quicker? Computing in the SQL Query ((a+b+c+d+e+f+g+h+i)/(j+k)), calling ComputeScalarUnitCost(datapoint.ID) 4 times, or joining to ComputeUnitCostTable(datapoint.ID) one time?

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  • Does it make sense to replace sub-queries by join?

    - by Roman
    For example I have a query like that. select col1 from t1 where col2>0 and col1 in (select col1 from t2 where col2>0) As far as I understand, I can replace it by the following query: select t1.col1 from t1 join (select col1 from t2 where col2>0) as t2 on t1.col1=t2.col1 where t1.col2>0 ADDED In some answers I see join in other inner join. Are both right? Or they are even identical?

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  • Improve C function performance with cache locality?

    - by Christoper Hans
    I have to find a diagonal difference in a matrix represented as 2d array and the function prototype is int diagonal_diff(int x[512][512]) I have to use a 2d array, and the data is 512x512. This is tested on a SPARC machine: my current timing is 6ms but I need to be under 2ms. Sample data: [3][4][5][9] [2][8][9][4] [6][9][7][3] [5][8][8][2] The difference is: |4-2| + |5-6| + |9-5| + |9-9| + |4-8| + |3-8| = 2 + 1 + 4 + 0 + 4 + 5 = 16 In order to do that, I use the following algorithm: int i,j,result=0; for(i=0; i<4; i++) for(j=0; j<4; j++) result+=abs(array[i][j]-[j][i]); return result; But this algorithm keeps accessing the column, row, column, row, etc which make inefficient use of cache. Is there a way to improve my function?

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  • How to optimize method's that track metrics in 3rd party application?

    - by WulfgarPro
    Hi, I have two listboxes that keep updated lists of various objects roaming in a 3rd party application. When a user selects an object from a listbox, an event handler is fired, calling a method that gathers various metrics belonging to that object from the 3rd party application for displaying in a set of textboxes. This is slow! I am not sure how to optimize this functionality to facilitate greater speeds.. private void lsbUavs_SelectedIndexChanged(object sender, EventArgs e) { if (_ourSelectedUavFromListBox != null) { UtilStkScenario.ChangeUavColourOnScenario(_ourSelectedUavFromListBox.UavName, false); } if (lsbUavs.SelectedItem != null) { Uav ourUav = UtilStkScenario.FindUavFromScenarioBasedOnName(lsbUavs.SelectedItem.ToString()); hsbThrottle.Value = (int)ourUav.ThrottleValue; UtilStkScenario.ChangeUavColourOnScenario(ourUav.UavName, true); _ourSelectedUavFromListBox = ourUav; // we don't want this thread spawning many times if (tUpdateMetricInformationInTabControl != null) { if (tUpdateMetricInformationInTabControl.IsAlive) { tUpdateMetricInformationInTabControl.Abort(); } } tUpdateMetricInformationInTabControl = new Thread(UpdateMetricInformationInTabControl); tUpdateMetricInformationInTabControl.Name = "UpdateMetricInformationInTabControlUavs"; tUpdateMetricInformationInTabControl.IsBackground = true; tUpdateMetricInformationInTabControl.Start(lsbUavs); } } delegate string GetNameOfListItem(ListBox listboxId); delegate void SetTextBoxValue(TextBox textBoxId, string valueToSet); private void UpdateMetricInformationInTabControl(object listBoxToUpdate) { ListBox theListBoxToUpdate = (ListBox)listBoxToUpdate; GetNameOfListItem dGetNameOfListItem = new GetNameOfListItem(GetNameOfSelectedListItem); SetTextBoxValue dSetTextBoxValue = new SetTextBoxValue(SetNamedTextBoxValue); try { foreach (KeyValuePair<string, IAgStkObject> entity in UtilStkScenario._totalListOfAllStkObjects) { if (entity.Key.ToString() == (string)theListBoxToUpdate.Invoke(dGetNameOfListItem, theListBoxToUpdate)) { while ((string)theListBoxToUpdate.Invoke(dGetNameOfListItem, theListBoxToUpdate) == entity.Key.ToString()) { if (theListBoxToUpdate.Name == "lsbEntities") { double[] latLonAndAltOfEntity = UtilStkScenario.FindMetricsOfStkObjectOnScenario(UtilStkScenario._stkObjectRoot.CurrentTime, entity.Value); SetEntityOrUavMetricValuesInTextBoxes(dSetTextBoxValue, "Entity", entity.Key, "", "", "", "", latLonAndAltOfEntity[4].ToString(), latLonAndAltOfEntity[3].ToString()); } else if (theListBoxToUpdate.Name == "lsbUavs") { double[] latLonAndAltOfEntity = UtilStkScenario.FindMetricsOfStkObjectOnScenario(UtilStkScenario._stkObjectRoot.CurrentTime, entity.Value); SetEntityOrUavMetricValuesInTextBoxes(dSetTextBoxValue, "UAV", entity.Key, entity.Value.ClassName.ToString(), latLonAndAltOfEntity[0].ToString(), latLonAndAltOfEntity[1].ToString(), latLonAndAltOfEntity[2].ToString(), latLonAndAltOfEntity[4].ToString(), latLonAndAltOfEntity[3].ToString()); } } } } } catch (Exception e) { // selected entity was deleted(end-of-life) in STK - remove LLA information from GUI if (theListBoxToUpdate.Name == "lsbEntities") { SetEntityOrUavMetricValuesInTextBoxes(dSetTextBoxValue, "Entity", "", "", "", "", "", "", ""); UtilLog.Log(e.Message.ToString(), e.GetType().ToString(), "UpdateMetricInformationInTabControl", UtilLog.logWriter); } else if (theListBoxToUpdate.Name == "lsbUavs") { SetEntityOrUavMetricValuesInTextBoxes(dSetTextBoxValue, "UAV", "", "", "", "", "", "", ""); UtilLog.Log(e.Message.ToString(), e.GetType().ToString(), "UpdateMetricInformationInTabControl", UtilLog.logWriter); } } } internal static double[] FindMetricsOfStkObjectOnScenario(object timeToFindMetricState, IAgStkObject stkObject) { double[] stkObjectMetrics = null; try { stkObjectMetrics = new double[5]; object latOfStkObject, lonOfStkObject; double altOfStkObject, headingOfStkObject, velocityOfStkObject; IAgProvideSpatialInfo spatial = stkObject as IAgProvideSpatialInfo; IAgVeSpatialInfo spatialInfo = spatial.GetSpatialInfo(false); IAgSpatialState spatialState = spatialInfo.GetState(timeToFindMetricState); spatialState.FixedPosition.QueryPlanetodetic(out latOfStkObject, out lonOfStkObject, out altOfStkObject); double[] stkObjectheadingAndVelocity = FindHeadingAndVelocityOfStkObjectFromScenario(stkObject.InstanceName); headingOfStkObject = stkObjectheadingAndVelocity[0]; velocityOfStkObject = stkObjectheadingAndVelocity[1]; stkObjectMetrics[0] = (double)latOfStkObject; stkObjectMetrics[1] = (double)lonOfStkObject; stkObjectMetrics[2] = altOfStkObject; stkObjectMetrics[3] = headingOfStkObject; stkObjectMetrics[4] = velocityOfStkObject; } catch (Exception e) { UtilLog.Log(e.Message.ToString(), e.GetType().ToString(), "FindMetricsOfStkObjectOnScenario", UtilLog.logWriter); } return stkObjectMetrics; } private static double[] FindHeadingAndVelocityOfStkObjectFromScenario(string stkObjectName) { double[] stkObjectHeadingAndVelocity = new double[2]; IAgStkObject stkUavObject = null; try { string typeOfObject = CheckIfStkObjectIsEntityOrUav(stkObjectName); if (typeOfObject == "UAV") { stkUavObject = _stkObjectRootToIsolateForUavs.CurrentScenario.Children[stkObjectName]; IAgDataProviderGroup group = (IAgDataProviderGroup)stkUavObject.DataProviders["Heading"]; IAgDataProvider provider = (IAgDataProvider)group.Group["Fixed"]; IAgDrResult result = ((IAgDataPrvTimeVar)provider).ExecSingle(_stkObjectRootToIsolateForUavs.CurrentTime); stkObjectHeadingAndVelocity[0] = (double)result.DataSets[1].GetValues().GetValue(0); stkObjectHeadingAndVelocity[1] = (double)result.DataSets[4].GetValues().GetValue(0); } else if (typeOfObject == "Entity") { IAgStkObject stkEntityObject = _stkObjectRootToIsolateForEntities.CurrentScenario.Children[stkObjectName]; IAgDataProviderGroup group = (IAgDataProviderGroup)stkEntityObject.DataProviders["Heading"]; IAgDataProvider provider = (IAgDataProvider)group.Group["Fixed"]; IAgDrResult result = ((IAgDataPrvTimeVar)provider).ExecSingle(_stkObjectRootToIsolateForEntities.CurrentTime); stkObjectHeadingAndVelocity[0] = (double)result.DataSets[1].GetValues().GetValue(0); stkObjectHeadingAndVelocity[1] = (double)result.DataSets[4].GetValues().GetValue(0); } } catch (Exception e) { UtilLog.Log(e.Message.ToString(), e.GetType().ToString(), "FindHeadingAndVelocityOfStkObjectFromScenario", UtilLog.logWriter); } return stkObjectHeadingAndVelocity; } Any help would be really appreciated. From my knowledge, I cant really see any issues with the C#. Maybe it has to do with the methodology I'm using.. maybe some kind of caching mechanism is required - this is not natively available. WulfgarPro

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  • Why is i-- faster than i++ in loops? [closed]

    - by Afshin Mehrabani
    Possible Duplicate: JavaScript - Are loops really faster in reverse…? I don't know if this question is valid in other languages or not, but I'm asking this specifically for JavaScript. I see in some articles and questions that the fastest loop in JavaScript is something like: for(var i = array.length; i--; ) Also in Sublime Text 2, when you try to write a loop, it suggests: for (var i = Things.length - 1; i >= 0; i--) { Things[i] }; I want to know, why is i-- faster than i++ in loops?

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  • Help optimizing a query with 16 subqueries

    - by Webnet
    I have indexes/primaries on all appropriate ID fields for each type. I'm wondering though how I could make this more efficient. It takes a while to load the page with only 15,000 rows and that'll quickly grow to 500k. The $whereSql variable simply has a few more parameters for the main ebay_archive_listing table. NOTE: This is all done in a single query because I have ASC/DESC sorting for each subquery value. NOTE: I've converted some of the sub queries to INNER JOIN's SELECT product_master.product_id, ( SELECT COUNT(listing_id) FROM ebay_archive_product_listing_assoc '.$listingCountJoin.' WHERE ebay_archive_product_listing_assoc.product_id = product_master.product_id) as listing_count, sku, type_id, ( SELECT AVG(ebay_archive_listing.current_price) FROM ebay_archive_listing INNER JOIN ebay_archive_product_listing_assoc ON ( ebay_archive_product_listing_assoc.listing_id = ebay_archive_listing.id AND ebay_archive_product_listing_assoc.product_id = product_master.product_id ) WHERE '.$whereSql.' AND ebay_archive_listing.current_price > 0 ) as average_bid_price, ( SELECT AVG(ebay_archive_listing.buy_it_now_price) FROM ebay_archive_listing INNER JOIN ebay_archive_product_listing_assoc ON ( ebay_archive_product_listing_assoc.listing_id = ebay_archive_listing.id AND ebay_archive_product_listing_assoc.product_id = product_master.product_id ) WHERE '.$whereSql.' AND ebay_archive_listing.buy_it_now_price > 0 ) as average_buyout_price, ( SELECT MIN(ebay_archive_listing.current_price) FROM ebay_archive_listing INNER JOIN ebay_archive_product_listing_assoc ON ( ebay_archive_product_listing_assoc.listing_id = ebay_archive_listing.id AND ebay_archive_product_listing_assoc.product_id = product_master.product_id ) WHERE '.$whereSql.' AND ebay_archive_listing.current_price > 0 ) as lowest_bid_price, ( SELECT MAX(ebay_archive_listing.current_price) FROM ebay_archive_listing INNER JOIN ebay_archive_product_listing_assoc ON ( ebay_archive_product_listing_assoc.listing_id = ebay_archive_listing.id AND ebay_archive_product_listing_assoc.product_id = product_master.product_id ) WHERE '.$whereSql.' AND ebay_archive_listing.current_price > 0 ) as highest_bid_price, ( SELECT MIN(ebay_archive_listing.buy_it_now_price) FROM ebay_archive_listing INNER JOIN ebay_archive_product_listing_assoc ON ( ebay_archive_product_listing_assoc.listing_id = ebay_archive_listing.id AND ebay_archive_product_listing_assoc.product_id = product_master.product_id ) WHERE '.$whereSql.' AND ebay_archive_listing.current_price > 0 ) as lowest_buyout_price, ( SELECT MAX(ebay_archive_listing.buy_it_now_price) FROM ebay_archive_listing INNER JOIN ebay_archive_product_listing_assoc ON ( ebay_archive_product_listing_assoc.listing_id = ebay_archive_listing.id AND ebay_archive_product_listing_assoc.product_id = product_master.product_id ) WHERE '.$whereSql.' AND ebay_archive_listing.current_price > 0 ) as highest_buyout_price, round((( SELECT COUNT(ebay_archive_listing.id) FROM ebay_archive_listing INNER JOIN ebay_archive_product_listing_assoc ON ( ebay_archive_product_listing_assoc.listing_id = ebay_archive_listing.id AND ebay_archive_product_listing_assoc.product_id = product_master.product_id ) WHERE '.$whereSql.' AND ebay_archive_listing.status_id = 2 ) / ( SELECT COUNT(listing_id) FROM ebay_archive_product_listing_assoc '.$listingCountJoin.' WHERE ebay_archive_product_listing_assoc.product_id = product_master.product_id ) * 100), 1) as sold_percent FROM product_master '.$joinSql.' WHERE product_master.product_id IN ( SELECT product_id FROM ebay_archive_product_listing_assoc INNER JOIN ebay_archive_listing ON ( ebay_archive_listing.id = ebay_archive_product_listing_assoc.listing_id AND '.$whereSql.' ) )

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