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  • Long-running Database Query

    - by JamesMLV
    I have a long-running SQL Server 2005 query that I have been hoping to optimize. When I look at the actual execution plan, it says a Clustered Index Seek has 66% of the cost. Execuation Plan Snippit: <RelOp AvgRowSize="31" EstimateCPU="0.0113754" EstimateIO="0.0609028" EstimateRebinds="0" EstimateRewinds="0" EstimateRows="10198.5" LogicalOp="Clustered Index Seek" NodeId="16" Parallel="false" PhysicalOp="Clustered Index Seek" EstimatedTotalSubtreeCost="0.0722782"> <OutputList> <ColumnReference Database="[wf_1]" Schema="[dbo]" Table="[Indices]" Alias="[I]" Column="quoteDate" /> <ColumnReference Database="[wf_1]" Schema="[dbo]" Table="[Indices]" Alias="[I]" Column="price" /> <ColumnReference Database="[wf_1]" Schema="[dbo]" Table="[Indices]" Alias="[I]" Column="tenure" /> </OutputList> <RunTimeInformation> <RunTimeCountersPerThread Thread="0" ActualRows="1067" ActualEndOfScans="1" ActualExecutions="1" /> </RunTimeInformation> <IndexScan Ordered="true" ScanDirection="FORWARD" ForcedIndex="false" NoExpandHint="false"> <DefinedValues> <DefinedValue> <ColumnReference Database="[wf_1]" Schema="[dbo]" Table="[Indices]" Alias="[I]" Column="quoteDate" /> </DefinedValue> <DefinedValue> <ColumnReference Database="[wf_1]" Schema="[dbo]" Table="[Indices]" Alias="[I]" Column="price" /> </DefinedValue> <DefinedValue> <ColumnReference Database="[wf_1]" Schema="[dbo]" Table="[Indices]" Alias="[I]" Column="tenure" /> </DefinedValue> </DefinedValues> <Object Database="[wf_1]" Schema="[dbo]" Table="[Indices]" Index="[_dta_index_Indices_14_320720195__K5_K2_K1_3]" Alias="[I]" /> <SeekPredicates> <SeekPredicate> <Prefix ScanType="EQ"> <RangeColumns> <ColumnReference Database="[wf_1]" Schema="[dbo]" Table="[Indices]" Alias="[I]" Column="HedgeProduct" ComputedColumn="true" /> </RangeColumns> <RangeExpressions> <ScalarOperator ScalarString="(1)"> <Const ConstValue="(1)" /> </ScalarOperator> </RangeExpressions> </Prefix> <StartRange ScanType="GE"> <RangeColumns> <ColumnReference Database="[wf_1]" Schema="[dbo]" Table="[Indices]" Alias="[I]" Column="tenure" /> </RangeColumns> <RangeExpressions> <ScalarOperator ScalarString="[@StartMonth]"> <Identifier> <ColumnReference Column="@StartMonth" /> </Identifier> </ScalarOperator> </RangeExpressions> </StartRange> <EndRange ScanType="LE"> <RangeColumns> <ColumnReference Database="[wf_1]" Schema="[dbo]" Table="[Indices]" Alias="[I]" Column="tenure" /> </RangeColumns> <RangeExpressions> <ScalarOperator ScalarString="[@EndMonth]"> <Identifier> <ColumnReference Column="@EndMonth" /> </Identifier> </ScalarOperator> </RangeExpressions> </EndRange> </SeekPredicate> </SeekPredicates> </IndexScan> </RelOp> From this, does anyone see an obvious problem that would be causing this to take so long? Here is the query: (SELECT quotedate, tenure, price, ActualVolume, HedgePortfolioValue, Price AS UnhedgedPrice, ((ActualVolume*Price - HedgePortfolioValue)/ActualVolume) AS HedgedPrice FROM ( SELECT [quoteDate] ,[price] , tenure ,isnull(wf_1.[Risks].[HedgePortValueAsOfDate2](1,tenureMonth,quotedate,price),0) as HedgePortfolioValue ,[TotalOperatingGasVolume] as ActualVolume FROM [wf_1].[dbo].[Indices] I inner join ( SELECT DISTINCT tenureMonth FROM [wf_1].[Risks].[KnowRiskTrades] WHERE HedgeProduct = 1 AND portfolio <> 'Natural Gas Hedge Transactions' ) B ON I.tenure=B.tenureMonth inner join ( SELECT [Month],[TotalOperatingGasVolume] FROM [wf_1].[Risks].[ActualGasVolumes] ) C ON C.[Month]=B.tenureMonth WHERE HedgeProduct = 1 AND quoteDate>=dateadd(day, -3*365, tenureMonth) AND quoteDate<=dateadd(day,-3,tenureMonth) )A )

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  • Will the compiler optimize escaping an inner loop?

    - by BCS
    The code I have looks like this (all uses of done shown): bool done = false; for(int i = 0; i < big; i++) { ... for(int j = 0; j < wow; j++) { ... if(foo(i,j)) { done = true; break; } ... } if(done) break; ... } will any compilers convert it to this: for(int i = 0; i < big; i++) { ... for(int j = 0; j < wow; j++) { ... if(foo(i,j)) goto __done; // same as a labeled break if we had it ... } ... } __done:;

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  • MySQL subqueries

    - by swamprunner7
    Can we do this query without subqueries? SELECT login, post_n, (SELECT SUM(vote) FROM votes WHERE votes.post_n=posts.post_n)AS votes, (SELECT COUNT(comments.post_n) FROM comments WHERE comments.post_n=posts.post_n)AS comments_count FROM users, posts WHERE posts.id=users.id AND (visibility=2 OR visibility=3) ORDER BY date DESC LIMIT 0, 15 tables: Users: id, login Posts: post_n, id, visibility Votes: post_n, vote id — it`s user id, Users the main table.

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  • Database indexes - what should they be

    - by WebweaverD
    Most of my database tables have a clear unique index through which lookups are done 90% of the time but I am a bit unsure on this one - I have a table which keeps track of user rating totals for items in my database, I now want to add another table, to track individual ratings with an ip address column to make sure no one can rate something twice. Since I can see this becoming a big, high use table it is important to optimize it correctly. (MYSQL table) This table will have the following fields: rating_id(always - unique), item_id (always - not unique), user_id (optional - not unique), ip_address (always - not unique), rating_value(always - not unique), has_review(bool) Now I envisions 90% the queries going something like this: When a user rates something - select where item_id = x and ip_address = y, (if rows = 0) insert rating When in user account pages - select where ip_address = x or username = y Now none of the fields searched on are unique, can I still use them as indexes (for example item _id and ip_address), can I have two indexes and will this still improve performance over a non indexed table?

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  • Access violation using LocalAlloc()

    - by PaulH
    I have a Visual Studio 2008 Windows Mobile 6 C++ application that is using an API that requires the use of LocalAlloc(). To make my life easier, I created an implementation of a standard allocator that uses LocalAlloc() internally: /// Standard library allocator implementation using LocalAlloc and LocalReAlloc /// to create a dynamically-sized array. /// Memory allocated by this allocator is never deallocated. That is up to the /// user. template< class T, int max_allocations > class LocalAllocator { public: typedef T value_type; typedef size_t size_type; typedef ptrdiff_t difference_type; typedef T* pointer; typedef const T* const_pointer; typedef T& reference; typedef const T& const_reference; pointer address( reference r ) const { return &r; }; const_pointer address( const_reference r ) const { return &r; }; LocalAllocator() throw() : c_( NULL ) { }; /// Attempt to allocate a block of storage with enough space for n elements /// of type T. n>=1 && n<=max_allocations. /// If memory cannot be allocated, a std::bad_alloc() exception is thrown. pointer allocate( size_type n, const void* /*hint*/ = 0 ) { if( NULL == c_ ) { c_ = LocalAlloc( LPTR, sizeof( T ) * n ); } else { HLOCAL c = LocalReAlloc( c_, sizeof( T ) * n, LHND ); if( NULL == c ) LocalFree( c_ ); c_ = c; } if( NULL == c_ ) throw std::bad_alloc(); return reinterpret_cast< T* >( c_ ); }; /// Normally, this would release a block of previously allocated storage. /// Since that's not what we want, this function does nothing. void deallocate( pointer /*p*/, size_type /*n*/ ) { // no deallocation is performed. that is up to the user. }; /// maximum number of elements that can be allocated size_type max_size() const throw() { return max_allocations; }; private: /// current allocation point HLOCAL c_; }; // class LocalAllocator My application is using that allocator implementation in a std::vector< #define MAX_DIRECTORY_LISTING 512 std::vector< WIN32_FIND_DATA, LocalAllocator< WIN32_FIND_DATA, MAX_DIRECTORY_LISTING > > file_list; WIN32_FIND_DATA find_data = { 0 }; HANDLE find_file = ::FindFirstFile( folder.c_str(), &find_data ); if( NULL != find_file ) { do { // access violation here on the 257th item. file_list.push_back( find_data ); } while ( ::FindNextFile( find_file, &find_data ) ); ::FindClose( find_file ); } // data submitted to the API that requires LocalAlloc()'d array of WIN32_FIND_DATA structures SubmitData( &file_list.front() ); On the 257th item added to the vector<, the application crashes with an access violation: Data Abort: Thread=8e1b0400 Proc=8031c1b0 'rapiclnt' AKY=00008001 PC=03f9e3c8(coredll.dll+0x000543c8) RA=03f9ff04(coredll.dll+0x00055f04) BVA=21ae0020 FSR=00000007 First-chance exception at 0x03f9e3c8 in rapiclnt.exe: 0xC0000005: Access violation reading location 0x01ae0020. LocalAllocator::allocate is called with an n=512 and LocalReAlloc() succeeds. The actual Access Violation exception occurs within the std::vector< code after the LocalAllocator::allocate call: 0x03f9e3c8 0x03f9ff04 > MyLib.dll!stlp_std::priv::__copy_trivial(const void* __first = 0x01ae0020, const void* __last = 0x01b03020, void* __result = 0x01b10020) Line: 224, Byte Offsets: 0x3c C++ MyLib.dll!stlp_std::vector<_WIN32_FIND_DATAW,LocalAllocator<_WIN32_FIND_DATAW,512> >::_M_insert_overflow(_WIN32_FIND_DATAW* __pos = 0x01b03020, _WIN32_FIND_DATAW& __x = {...}, stlp_std::__true_type& __formal = {...}, unsigned int __fill_len = 1, bool __atend = true) Line: 112, Byte Offsets: 0x5c C++ MyLib.dll!stlp_std::vector<_WIN32_FIND_DATAW,LocalAllocator<_WIN32_FIND_DATAW,512> >::push_back(_WIN32_FIND_DATAW& __x = {...}) Line: 388, Byte Offsets: 0xa0 C++ MyLib.dll!Foo(unsigned long int cbInput = 16, unsigned char* pInput = 0x01a45620, unsigned long int* pcbOutput = 0x1dabfbbc, unsigned char** ppOutput = 0x1dabfbc0, IRAPIStream* __formal = 0x00000000) Line: 66, Byte Offsets: 0x1e4 C++ If anybody can point out what I may be doing wrong, I would appreciate it. Thanks, PaulH

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  • NSAutoreleasePool carrying across methods?

    - by Tim
    I'm building an iPhone application where I detach some threads to do long-running work in the background so as not to hang the UI. I understand that threads need NSAutoreleasePool instances for memory management. What I'm not sure about is if the threaded method calls another method - does that method also need an NSAutoreleasePool? Example code: - (void)primaryMethod { [self performSelectorInBackground:@selector(threadedMethod) withObject:nil]; } - (void)threadedMethod { NSAutoreleasePool *aPool = [[NSAutoreleasePool alloc] init]; // Some code here [self anotherMethod]; // Maybe more code here [aPool drain]; } - (void)anotherMethod { // More code here } The reason I ask is I'm receiving errors that objects are being autoreleased with no pool in place, and are "just leaking." I've seen other questions where people didn't have autorelease pools in place at all, and I understand why an autorelease pool is needed. I'm specifically interested in finding out whether an autorelease pool created in (in this example) threadedMethod applies to objects created in anotherMethod.

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  • Javascriptlibrary more efficient than Rickshaw for realtime visualizations

    - by dan kutz
    I want to visualize data as time-series graphs on mobile devices(tablets) and therefore stumbled upon rickshaw, which is based on D3. First I must say I was a little bit confused when I realized that realtime in web design is defined totally different to realtime in engineering which has fixed(and often very short) timeframes. Anyway my aim is to visualize the data as fast as possible, and on older tablets visualization with rickshaw is quite slow. Can anybody recommend another library, which may be more efficient in rendering? Or is there no way out and I have to go native? regards Dan.

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  • Release an object without a pointer?

    - by Kai Friis
    I’ve just started developing for iPhone and am trying to get my head around memory management. I made a small program that shows a map and an annotation on the map. For the annotation I made a simple class that implements the MKAnnotation protocol. To create and add the annotation I wrote this: [self.myMapView addAnnotation:[[MyAnnotation alloc] init]]; It worked fine until I tried to release the object. Nothing to release. This is what I would have done in C#, I guess it doesn’t work without garbage collection? So is this the only way to do it? MyAnnotation *myAnnotation = [[MyAnnotation alloc] init]; [self.myMapView addAnnotation: myAnnotation]; [myAnnotation release];

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  • Hierarchical Hibernate, how many queries are executed?

    - by ghost1
    So I've been dealing with a home brew DB framework that has some seriously flaws, the justification for use being that not using an ORM will save on the number of queries executed. If I'm selecting all possibile records from the top level of a joinable object hierarchy, how many separate calls to the DB will be made when using an ORM (such as Hibernate)? I feel like calling bullshit on this, as joinable entities should be brought down in one query , right? Am I missing something here? note: lazy initialization doesn't matter in this scenario as all records will be used.

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  • MySQL won't use index for query?

    - by Jack Sleight
    I have this table: CREATE TABLE `point` ( `id` INT(11) NOT NULL AUTO_INCREMENT, `siteid` INT(11) NOT NULL, `lft` INT(11) DEFAULT NULL, `rgt` INT(11) DEFAULT NULL, `level` SMALLINT(6) DEFAULT NULL, PRIMARY KEY (`id`), KEY `point_siteid_site_id` (`siteid`), CONSTRAINT `point_siteid_site_id` FOREIGN KEY (`siteid`) REFERENCES `site` (`id`) ON DELETE CASCADE ) ENGINE=INNODB AUTO_INCREMENT=35 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci And this query: SELECT * FROM `point` WHERE siteid = 1; Which results in this EXPLAIN information: +----+-------------+-------+------+----------------------+------+---------+------+------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+----------------------+------+---------+------+------+-------------+ | 1 | SIMPLE | point | ALL | point_siteid_site_id | NULL | NULL | NULL | 6 | Using where | +----+-------------+-------+------+----------------------+------+---------+------+------+-------------+ Question is, why isn't the query using the point_siteid_site_id index?

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  • How to store static content across branches in a single location in version control

    - by Shravan
    [Just a random thought] I have a pdf doc that is downloaded when the user clicks on 'help' on my website. Now, this is a pretty huge document and is saved in version control (SVN) and is thus copied for all branches that exist in SVN. This is static content and something that developers are not working on, and does not change often. Is there a more efficient way to store it (that would not hamper local deployments) that would make SVN checkouts and updates relatively faster. I know the benefit we get is not huge, this is something that came to my head none the less.

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  • Optimizing an embedded SELECT query in mySQL

    - by Crazy Serb
    Ok, here's a query that I am running right now on a table that has 45,000 records and is 65MB in size... and is just about to get bigger and bigger (so I gotta think of the future performance as well here): SELECT count(payment_id) as signup_count, sum(amount) as signup_amount FROM payments p WHERE tm_completed BETWEEN '2009-05-01' AND '2009-05-30' AND completed > 0 AND tm_completed IS NOT NULL AND member_id NOT IN (SELECT p2.member_id FROM payments p2 WHERE p2.completed=1 AND p2.tm_completed < '2009-05-01' AND p2.tm_completed IS NOT NULL GROUP BY p2.member_id) And as you might or might not imagine - it chokes the mysql server to a standstill... What it does is - it simply pulls the number of new users who signed up, have at least one "completed" payment, tm_completed is not empty (as it is only populated for completed payments), and (the embedded Select) that member has never had a "completed" payment before - meaning he's a new member (just because the system does rebills and whatnot, and this is the only way to sort of differentiate between an existing member who just got rebilled and a new member who got billed for the first time). Now, is there any possible way to optimize this query to use less resources or something, and to stop taking my mysql resources down on their knees...? Am I missing any info to clarify this any further? Let me know... EDIT: Here are the indexes already on that table: PRIMARY PRIMARY 46757 payment_id member_id INDEX 23378 member_id payer_id INDEX 11689 payer_id coupon_id INDEX 1 coupon_id tm_added INDEX 46757 tm_added, product_id tm_completed INDEX 46757 tm_completed, product_id

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  • Why is doing a top(1) on an indexed column in SQL Server slow?

    - by reinier
    I'm puzzled by the following. I have a DB with around 10 million rows, and (among other indices) on 1 column (campaignid_int) is an index. Now I have 700k rows where the campaignid is indeed 3835 For all these rows, the connectionid is the same. I just want to find out this connectionid. use messaging_db; SELECT TOP (1) connectionid FROM outgoing_messages WITH (NOLOCK) WHERE (campaignid_int = 3835) Now this query takes approx 30 seconds to perform! I (with my small db knowledge) would expect that it would take any of the rows, and return me that connectionid If I test this same query for a campaign which only has 1 entry, it goes really fast. So the index works. How would I tackle this and why does this not work? edit: estimated execution plan: select (0%) - top (0%) - clustered index scan (100%)

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  • How to make Visual C++ 9 not emit code that is actually never called?

    - by sharptooth
    My native C++ COM component uses ATL. In DllRegisterServer() I call CComModule::RegisterServer(): STDAPI DllRegisterServer() { return _Module.RegisterServer(FALSE); // <<< notice FALSE here } FALSE is passed to indicate to not register the type library. ATL is available as sources, so I in fact compile the implementation of CComModule::RegisterServer(). Somewhere down the call stack there's an if statement: if( doRegisterTypeLibrary ) { //<< FALSE goes here // do some stuff, then call RegisterTypeLib() } The compiler sees all of the above code and so it can see that in fact the if condition is always false, yet when I inspect the linker progress messages I see that the reference to RegisterTypeLib() is still there, so the if statement is not eliminated. Can I make Visual C++ 9 perform better static analysis and actually see that some code is never called and not emit that code?

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  • Is there a faster TList implementation ?

    - by dmauric.mp
    My application makes heavy use of TList, so I was wondering if there are any alternative implementations that are faster or optimized for particular use case. I know of RtlVCLOptimize.pas 2.77, which has optimized implementations of several TList methods. But I'd like to know if there is anything else out there. I also don't require it to be a TList descendant, I just need the TList functionality regardless of how it's implemented. It's entirely possible, given the rather basic functionality TList provides, that there is not much room for improvement, but would still like to verify that, hence this question.

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  • How can I Query only __key__ on a Google Appengine PolyModel child?

    - by Gabriel
    So the situation is: I want to optimize my code some for doing counting of records. So I have a parent Model class Base, a PolyModel class Entry, and a child class of Entry Article: How would I query Article.key so I can reduce the query load but only get the Article count. My first thought was to use: q = db.GqlQuery("SELECT __key__ from Article where base = :1", i_base) but it turns out GqlQuery doesn't like that because articles are actually stored in a table called Entry. Would it be possible to Query the class attribute? something like: q = db.GqlQuery("select __key__ from Entry where base = :1 and :2 in class", i_base, 'Article') neither of which work. Turns out the answer is even easier. But I am going to finish this question because I looked everywhere for this. q = db.GqlQuery("select __key__ from Entry where base = :1 and class = :2", i_base, 'Article')

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  • Does the order of columns in a query matter?

    - by James Simpson
    When selecting columns from a MySQL table, is performance affected by the order that you select the columns as compared to their order in the table (not considering indexes that may cover the columns)? For example, you have a table with rows uid, name, bday, and you have the following query. SELECT uid, name, bday FROM table Does MySQL see the following query any differently and thus cause any sort of performance hit? SELECT uid, bday, name FROM table

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  • In PHP is faster to get a value from an if statement or from an array?

    - by Vittorio Vittori
    Maybe this is a stupid question but what is faster? <?php function getCss1 ($id = 0) { if ($id == 1) { return 'red'; } else if ($id == 2) { return 'yellow'; } else if ($id == 3) { return 'green'; } else if ($id == 4) { return 'blue'; } else if ($id == 5) { return 'orange'; } else { return 'grey'; } } function getCss2 ($id = 0) { $css[] = 'grey'; $css[] = 'red'; $css[] = 'yellow'; $css[] = 'green'; $css[] = 'blue'; $css[] = 'orange'; return $css[$id]; } echo getCss1(3); echo getCss2(3); ?> I suspect is faster the if statement but I prefere to ask!

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  • Completely remove ViewState for specific pages

    - by Kerido
    Hi everybody, I have a site that features some pages which do not require any post-back functionality. They simply display static HTML and don't even have any associated code. However, since the Master Page has a <form runat="server"> tag which wraps all ContentPlaceHolders, the resulting HTML always contains the ViewState field, i.e: <input type="hidden" id="__VIEWSTATE" value="/wEPDwUKMjEwNDQyMTMxM2Rk0XhpfvawD3g+fsmZqmeRoPnb9kI=" /> I realize, that when decrypted, this string corresponds to the <form> tag which I cannot remove. However, I would still like to remove the ViewState field for pages that only display static HTML. Is it possible?

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  • Alternate User select interface in django admin to reduce page size on large site?

    - by David Eyk
    I have a Django-based site with roughly 300,000 User objects. Admin pages for objects with a ForeignKey field to User take a very long time to load as the resulting form is about 6MB in size. Of course, the resulting dropdown isn't particularly useful, either. Are there any off-the-shelf replacements for handling this case? I've been googling for a snippet or a blog entry, but haven't found anything yet. I'd like to have a smaller download size and a more usable interface.

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  • Why is Javascript's Math.floor the slowest way to calculate floor in Javascript?

    - by z5h
    I'm generally not a fan of microbenchmarks. But this one has a very interesting result. http://ernestdelgado.com/archive/benchmark-on-the-floor/ It suggests that Math.floor is the SLOWEST way to calculate floor in Javascript. ~~n, n|n, n&n all being faster. This seems pretty shocking as I would expect that people implementing Javascript in today's modern browsers would be some pretty smart people. Does floor do something important that the other methods fail to do? Is there any reason to use it?

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  • SEO Google - Navigation Title vs. Page Heading

    - by louism
    Hi, i was wondering if anyone knows if theres a connection between what a navigation item is named and the page heading it goes to - does this have an impact on SEO? so for example, if i had in my navigation menu an item called About Us, but when you click it you come to a page with the heading Learn Who We Are (i.e. wrapped in [h1] heading tags) because there isnt an exact one-to-one match, is that a bad thing in terms of SEO? thanks

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  • MySQL Paritioning performance

    - by Imran Pathan
    Measured performance on key partitioned tables and normal tables separately. But we couldn't find any performance improvement with partitioning. Queries are pruned. Using MySQL 5.1.47 on RHEL 4. Table details: UserUsage - Will have entries for user mobile number and data usage for each date. Mobile number and Date as PRI KEY. UserProfile - Queries prev table and stores summary for each mobile number. Mobile number PRI KEY. CREATE TABLE `UserUsage` ( `Msisdn` decimal(20,0) NOT NULL, `Date` date NOT NULL, . . PRIMARY KEY USING BTREE (`Msisdn`,`Date`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 PARTITION BY KEY(Msisdn) PARTITIONS 50; CREATE TABLE `UserProfile` ( `Msisdn` decimal(20,0) NOT NULL, . . PRIMARY KEY (`Msisdn`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 PARTITION BY KEY(Msisdn) PARTITIONS 50; Second table is updated by query select and order by date in first table in a perl program, query is select * from UserUsage where Msisdn=number order by Date desc limit 7 [Process data in perl] update UserProfile values(....) where Msisdn=number explain partition for select, shows row being scanned in a particular partition only. Is something wrong with partition design or queries as partitioning is taking almost same or more time compared to normal tables?

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  • Avoid the use of loops (for) with R

    - by albergali
    Hi, I'm working with R and I have a code like this: i<-1 j<-1 for (i in 1:10) for (j in 1:100) if (data[i] == paths[j,1]) cluster[i,4] <- paths[j,2] where : data is a vector with 100 rows and 1 column paths is a matrix with 100 rows and 5 columns cluster is a matrix with 100 rows and 5 columns My question is: how could I avoid the use of "for" loops to iterate through the matrix? I don't know whether apply functions (lapply, tapply...) are useful in this case. This is a problem when j=10000 for example, because execution time is very long. Thank you

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  • Splitting tables by field to optimize MySQL?

    - by AK
    Do splitting fields into multiple tables ever yield faster queries? Consider the following two scenarios: Table1 ----------- int PersonID text Value1 float Value2 or Table1 ----------- int PersonID text Value1 Table2 ----------- int PersonID float Value2 If Value1 and Value2 are always being displayed together, I imagine Table1 is always faster because the second schema would require two SELECT statements. But are there any situations where you would choose the second? If the number of records were expected to be really large?

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