node.js: nested for loops, string operations performance dismal

Question

I wrote a script to read a large string top to bottom, instead of left to right. When I run the code one core of my CPU pegs @100% and the code never finishes. If I uncomment out the console.log it spits out the letters slower and slower and pegs all 8 cores @100%, memory usage slowly rises until it's used up all 8GB on my system and then it crashes with an OOM error. I'm obviously doing something horribly wrong.

var haystack = 'SRASBPETHWTWHDZVPOAECJHGNXHRKZXRBMSDYGZGNZBBCOKVPPJKKAQECOLGBFIIKTPVSROCCWWGRWDEQTNFSKEDNFBFKWVEELVTBULWROMGTXSASKCTFJQFDOGRNMZEBLFSCFAFWXZVRGFAZHERUTMOETZZRYNUHSRTHEYIVQDXFNWDDSLSSGPFOMYRHBGKONPIWDTZUBBRAJZGBVUGMVZZTPRAXMLZSXYELKJZWXUYUQIUGGHISZHIGSUQHGHTICVWIJVXMUXOQHPDESKSPRJHQVVTRTNQEVUWKGGQDURAXZWTMYUYIISIOXLTHCISFFSNHZMCGEWMOWCHRQKYNDTDLFWERZLEPRLTNZSPFEDCDESQVMLWMXGCXPMSPTJGSXTXINFADZTBUNDIQWOAIGFKQAJWHINHMZCZVMTJJWGTSGGOIBOZCJGVURJETNXSXWEDUNJPVLPZTDIMSIZGQUJALJYWVLRDYDRWVHZNUNKOLAUPTBMKUNFQYLVQKOQIPPWVNDXENRCVABOTNEKKJPURYNAWAGIZFEHYQMOFICBCQKELTMUYVQPYPZKVBYPTLXRLMYEXGAPRCWDJHQASDQHRGSTIYGMEAWOBLFPSDBGGXFBGIARMGLYOFCZXILLFLCVKCKCXYBTKIYRHLPWXBNGLJYVIZHWPIQSQLHURYRRTBTUBYRMMEQULVVJFKRRZTZVOIKNXPIICBQGFPTETWVPVUKEQOVTCOUARDTAVZFSZWBSTWTQEGLIDKUVMTFRXHOWPPJHCEWMTHJRKXENFENKDMPEYVNEMQRDBGZDIBVYCCFLFMFPSXHHADOZWMMOJKQSYNAPOKLUPSALZVKPKVBRIAFOXSECFCULWPFNPKFGIBPAUEXEOHLTRWTLJMHEMIXSVZVRYZQXCUGNZGDSLXJSROSBAIWPKQGICVKSMAVUHZPIQHDQGLSMJUQYYAZQSVORXLRNMEOYUFAKGKHJFKQPBYKDSLYHKLCEWAQINPRGOGVCQBAKTVDZZNRSIKZVSRMFCDJSANSGNQZPPEZSIZCSQCPMIRBKJZFKVRVVNOLDSYGFLMNJHCGUZDRVHTLSJMCHZCQJUURVMEFABDKQEFYXYZEQUOLEOZWXDXXOXIFPLTFBGTKYTBVSSTJESKVIMHJSUDVKRKOJYOGWIXLODESHRMPYBWKRPFEUGIYXXGHDVYXPUBVSQPHRUSSCQDHAXMJNUNSFGHZANXDFFXDETLXVAUAPOCASOTONXBXIYFMSMUUPFGMYKWVFGTTQFSNUDFTIRWSVVEQHPVFRYPLGPGIEUMSSFONCONOPHSDWGFBIGPEKQBRPZWYLZLKCMWFOKLNQBYJREVFRLWFBDVIVIIVZUTQZOLDSNDUISKYGJTIGWYUQBXXTAPQMKULPXGCYFMZLNQDAWOBWOVTKXOABKZRWAZUDYYTYNDQAEJHEDPOYUANKWMUATXGCRRGEKDVTIGTFLQHQVFJBRIFKYLHDJUXLAMVELRZPNBSEBQUVHARMKVCLLDHHYYQNTXFIMFKRIMTJUEJOWIEIETZDADSGNJFDGGWKRJUXQXXKLOUSYMCTHLYIXSICFCRHFCXUSFOMCVSVYIIMCNEGHRMCZKWXPHFAMCTCBEBHQOBDXHAYNSVVZWAGTEIMVWRCCPNCCQGUWXIGCPZERUVJRQIZQYSMAUNHCVNROCDFORLNOWTLVTHADALVCOISZDFKNFMXQBMVUMFDFKDGNRQKZPXDJNZODBXFUAGEPCEQSLGAOSQZUHJXEQFTRLAWZUUROTADFEXJBGJCOPLRNLLHVTNPNPHJDYWEGBKVOZOFDYMYMHUNDMLIZOCLODMRBZORXZVTUAIDXZIGOLLMGUJLSOHSVDFEMDTXEUMIOITNSXVNXUWMNPFITZXAJBKUVMNLUOONUDQSWYUCZOZXOXAFRCWVMMBLFCPPHFTLEKHXQNWYMQYDLGHTSSGDCFIRSMVTJFKPLVLBWIFWBJQTKXBIMLRTGNABJDXWIEFLVCDLQTSWURMBASDXNXHBQTEBCUTGWVTHXDHRJYZZKNQEBPXRYMWAXEGRSRUCQHYIOVOYJUXPANVEAJEUKKYAWEZSPZYCQPPWXVNNPHIVSHSSYVJLUNDXAFPCXLOOTRYVLVGNIQVPZLBXAPWQGSCCXINWFTIVFGLMUTPRWQFJORMQYYIUUJZRLLFXATWFRCQDKDIFXZHCWJGYEROPRQTJGJJSTRRKAMAGGMZKKOPXYKUSNZVVHHNRAGAGWXZOIYKVMAQJELXWGUEWMTSJMOEZRUEGUBZELODZNCDASJZGOTXYZGVTVMRTVVSWHFEFVUJPCCGEJXWYYLBVZGIGCHRNQOEDELTDIUZPAGGJYPCEEKZNQSMDKNMRZFVBPLIRBFCCVLUGCVPLOPCWDZJZAMKFKRLXTKQJIZSNAQFUXMCLXPTBKNNWWKKBVLYQPFHVEHGXQEHPOWRIIWXGKVBFMMDOJNFMCCNWTALOTLCMFKXKGIKYHQIOUJOAIXEFIMWMKCTABKRCVTAFDLWIQFDUEYDOBFJOKXBKIIBCVIVILAWTFXHLUVTMGQEJEVKBAVMITJPVRGRCDSFLPXRFWGAJLGMSPAOUVMDUBXYWEOVMDNUOIMXGEVNKCALLWPPMNNMFOVTZOAPSDJFZECSDIHKXCYJCAGYKLPOWFTVSRDSBSGGWDNFSTRZQYKMOUDNTRGXFKJBLOECLUJQGRQWGUETMKOGUWCAHDHGGCBSWXTXMLJMJFJTKURTTCXNOOEBYYUVKPWXSNUKVCZOXJOMXXCLTZWBUDYMEJNTIPBTWJKJJLYQFGYRGYFUCTAICLKBYEHONSPSMXLLMZCMJQVOGKEZOYBDJIUHAFGCEIAPXAQVGSBIJVUDHTWPPEKMWWFEUCAQWFRHLCFTLPXVJNKFCTEXGKPZXQXOBKPDWOAFOZTBYGDVFAJXMQOHAPTLSNLKJIGZRFSBGMQBNBAHELRDEWUEWQVKVYZBPGQVOWYKZEGLJRLYHBETRZTEWBTGJBRUTBKNDGEAQEUTLZZSAMCMMVJWBPDKOSGPLVUKPZAQGJDKUIIPCVBOIBCXRAAANQSCBBYQNXRTCRNHJGMRYICLHDBXVXEGBFAEXOAABYDXFQTKPXVMQPHXLTXCVMLXDJPULJNOGVZFMYIRBFIEESIEJDBLYPARQERLKUEHYUGJIRKVQEFZLQUQXSKRNBZURWPLZSTPXISSJLUFZSMFXZIVESRSKEDNJEPGVPUBHLGWTKISYYJVQHXPHJDWDWQMAQWTZIBKCHEAETDYBJETTGZYHUURVERLLSCKUHSJMOAXTRYGKDXGISNNAHVQTEZKRKWAMMHAJGEJZOWZNEIZLZSSGLDGHXNEJPUBPPXNLJCKBFYDGXUPXITFATASDFNSHKWNZMQGXBBOSHEWBOWWCFKDCWVKWOTKMNEGJNOPURJJWAFPQOLNGBMAUCITMGZBOQIEUJEIOSNSMYQJTGVPFGXWCCCKDRRVDIHDYCTQHESHCTUUSSVQWMWTAOKIJALBPMGBEXZQFRIKAQVWBUXUNKBYMYSEXBNZHFHUSFGSKRQYZVKTALOHBMXSGHRUDUYSSMWFMPMMWFXCPISMWXIFEQSWTQQKUMZGOANSOASHGJBEKWLJBXENHHBWQQUCRQYNAATEWLTESGXPCWYFVQGGXTTPIBWSYRXBQGDXJMZFQRYDPKFPNYRQEFGFSZBGZRDVLHSYXTRTXFOIQIYBPFEXQDXBEPJNDPPBICIRTBBTLQUALXYUWPUDBVMJSOJPNEGIWXGCBFDZZSKWNAUIAXOVJJWULADOMBTGOTCIAYLIAGYTVVBZVVMYBWAJYQYCTNHUXYINPLAEIJCECYYBFIMUXXDGRKJADAFWWQKVSKLWKGPJPFZDCWNIHLERAIXHDIIIMDQPFTZVZTWYXYCUOCFFEYPBZRTSCPUQMWXGZVYCKTEVNJPBDUBXIUSUOOGGYGRTGAZTYRCGBKJFGXBRMDQGZXIGZDJCHWFORQKJJGUJTRIGIKOBYSRTIOUIAZWVHAWISDDWTICHGVEHSUTDFTGBIJUMXLNHLVXBOFPCEUOWQRDIELVYBAOAWLRCBJVKJCXYPJPGIJGNGJYUVFDNDCDBQXQMRYLIHDKYQHGBWBZOAOXPMALQZEWAAHGMSLSROAJPLGSIKFUSYRDJPQCOOQJTJVNPLIHJECIFUHIIEZYMJCQTCKUHSCJMUVDEZIMFEGOMRHVUVIVGMBERRPLGKWWOPLKRQIWJRZBYOSXROTLBUDGLWGKKWANWWIWJNQDCVOBSIPNXJEHKNUHSXCXDCCRSNBYZVXBUOAETHRQYYVQGLXWBWXYDRBFSBCNOSJHGTNSCIAXPCLOACAQGCBTXZGTCIDNGLAZCWXIFWKDYJWBKXDEUJZPQRLWASIKLSLFMERFKPXQYQFIRYHHUXSCWVLQZGSMLZUYOAFCUHMJIVDOEBHDKZYUDADMCHXQYIKUMKAPRPWSGDMNAGCSOOVPSCSWCENPBOCCJQXPBBDEHHVUVTFSLHGTKHASWGOUUQEDZYJOXUXELQAMKVNGAAJXMAHKARSLPRZGTDBKPRCXYHWWHWRRXXPRFKMJJNEYGHTMWCTNBQRCUAJPPPLPNJETEYDBRMLEIKLKGLJMUBPRLWIFEOOQCBGNOVMLMTZGYCGMSLCTKBVHJGUZLGYUJYXONOPRHMJEAHICJRUXILJAGNHHJXSLJTVMGGRNVKTDOJVHHXWZVJIEJCPPVKAVHWPCNBZTIMNVYGAKBJIGBNMLRAYUAHKJWCOISZHMGONXQAXWJZVQOGQUGAKJEXUNLTCDYRQWDGGOUUUUHWPRASTBFMSYGROSNLXLENLVETJKKSOLSMHVEUQRLJUDAMKJLWECCIHTUSPPTVXUVZZVDUVPVWNQUPLIHVDPUQVUIIGIYCFUANGHNOWQMSOQOMHLQNIKVQBGOQHHZFVCLPIYOXHIAXDLRZJGXAIJYNLVXEIAAIZXCUITPLABHDPJYZEOACHCRYUZNYNHPJPOPPGEKXJAAZLGPXJSNHNSQSPJRXZGYGSNDUWNJCQNPLJJGKIBUXGSPGUXZAWHYBWCDSQPWVTBCVDQRDXMXBMDVRXLPHGUFSTQPXOLOFIZKFDLJSUUUXCINQOYFULWDNUZCRJIOSRMOWVMMHNYNFBUKYXEFLIPBFEDPFJGHFXQYVUZBUNUJDLSWYREVCKMVQQVAATSRNUOSNABSMXRFVVMVTXITIYWUKTCDNZPYUGPPQOQRPDFMVUXMTKNZQWOJHWELRFYDFKTBGVVSZNBTDNPBFHAKKUFHZVUXRARYEKWUCYQXLIWONVNBYXNAQZBTVGWIDGTAWFBRMRVVKYAXJOTYYSQXZAJEOWWCOJXLBWSXGODJSUEOMYXHPUEPDYLWYJNDISRWYYFAGYMVSXPTGTTVWTFBSTFMFCYRLFISMGKAZVQBSNISILDCSLUGVWBBKWAXOPTHPJQFBTONDUMCCNEDSRBYOCIAMTLBAVESZQEAHGNFADENFWGWIGAQTOCSNXNSZNEVJMHVENBGUOOMMGCBGJBCPQPYMBHDKJPQDBLAMLLSGUEEFLNGNZJFQFZKONNDHXIUJDMBUNOVWSFBBJWRHIJSTMSQNSFPDJAXRARKGEDQDHWGZQWZRWPLWAUPUIGUXPAXHIKPDJLCQOMHRYRLJYOCSNAWRNCHSXHJTKNGMHYOHRFIYQJFSPJOMYBUPHUQJRWNQEESRWPGJKHZRNDZBQIQBNFSIAVIBDEWWSDRATKVZPBTTHJYASFTUCIIHZQTXEOTLJSVTZQWALTTBGQLPFSYITRVWMKCJOZWONQSZTPDLXESINYENYTAZYPVZPDBYGFDGEZTJPZVZDHTRKOTGZELUGEWSMYZFOSQEZNNSCVKWXCKBDDRMWFWUBJJHTVQVPARGEFMXCCKQLCOABKJYOKUPJYQNMKNDBNROJDPUANZUTBZRKPCOFJHKHJQWQZMNFOLTJVODPWFPJOEYBLPIOIWFQOETPAAZEHMYSNMSSFSTIWOZRTGGXHDKJPOKCDUCFOZJNQAUUZJONRAOJHVPQDMUHNFRBHECDFCAOLXXQBDEPIZWQHMONFDLDQDAHAZRHGJTXVUPDPZVNHJHSGBPMVFVAHYUYKRPQVSTNSQXEBMSSKJBYQKBXWSNAQZJSYPQDCRFORMTTBVWUBPYIXLLMZEOMAELSCBIMRASXWFFFFZDHEUDIRZKJMNNENEARMVLNGYGJMCAOWYICCTRIQUJAWWLAPFTBJGHHEHBVQJNIDKAGMPOLTZIKEEBQTQHFVDIAHJEZMIFWPMXTEHJQKGMHMMYPYQCARDOZERLTHGYWWJJEILSYLISWVPRSCIUXVXKSQWLKTRCWUURCLGXYQQXWQVOWXTLURZIKQRJXTPNWRNQAYMIMMUXCTZREGGHFXMMAAHZZMQIEQGBHORJGAAZAJNZIDKKXZIRRTUASAEOBPBWYDUCUILWFEUMSBCPWWMNDCEFNSDJBGVDYUOUPPLEMTQLOLVXLPFNMYNCTSSIJRLQDOWSUEREYCVPKJVBTAVKEANLCJVZHRUIOEWBCUYDLEYYDLYEYYMOUTROZIGJRHRNLISBLUGUNLZZLNHIWTDNGRLAVPOLOYSMTTLLPKDLQWNSXMIDXBHAXYEMRPYONJVJLYPFLMLOSLWTRMSHLYMSRJHXKXRGWGAIXBUCWRXCGEUWYUIUSQQPWKMHHSBDFSYZKOSQZXXAVXXXJKFCNIGXEQZNBBKEKCQOWQGQHTUIPEYUFJARTKKFHDOUHLHUZZFXLWHIOOIGKNPAXEXDNWIUQSOSBHDEQLKPLIRUQMUBHSQIGUNJSBWHLBFSUOTNJZWQDDXETAQNDYADEIGPJEBVGIDGLVDMIECXNUIELRZAUFRBSMNPOGJHHCDAVVKIYEOWLLAVCUZOCBDKPAPCUVHWXUQSUASGIBQAOROBZLGTAMIHSHOWXPQBVFCOSNQLMFGEZAZRXTIHWDWXATHYUAIDPSGBPUIVVROEXXUHHVCCCMNXFGAQIJNNVZHBEWULPGLYJHLRBFGPPJCAIAFKALYQDWBFGDYRCOQGXZLVLSMMDXEKDCMQIQBQVRGVHTYUZTHGATYRZVIGUMKADPIGSIFJZCKKJHEONIKRXKOPXAGMWBMHVPVPDWRADGMTVERKRWSSVLVFIJGMUBZTRSPNGDLFRBXGMHNEOJCMPFOAPWEPLGRABYLLXDLTERRBKDBVYGQNDYYNCHLWDWWYLLVQBOVIHFJLFVTMKDVINYKKERJKSCZTZEKQSFOSMPNVGSNQSQNDAVQJNNLQHJLBTXPZBXFYRRACYWMCKFORKWGNJCLFIXCIQSPWUWTRLJSICZVKZDAIQTURXNBGDLIREHDLDUCDNDXNSHRCLQLATVPHOZRTIXXIQYEJSARNKOOYIIFVLEGISMMEQNCMAKQLXRQRNEKMGFLCNCJWCTRDMEIFCZVJGTLGWDSTBSEUKVWEIHOHMSZKXUCCVHACKLKQJQSXKUJXPTSHKYRMUADWABQSVKIPFRPTDASYVGJXXMSHFNGRDXIQFGCUGHLKOWXPJETKDWUZHZFKEDYTKZEUUQDIJMWKYUVDYZPTWSHNJDBLZMNOTKGCWFRASJBPQYPTAKPDBFPFLZCEPKPTHTQAQVMMFXUUNEGOJOYRCSBIZZPEREIYMQYMBJIDTYCJAJVIQGHLHVYVLFXRJJWEJJEGVJOYCBVQEVXKEDKLRFSOMXWEKBCHEMLCIVTZXXTJOXHPZAIMBTJBHVSOGNWZBRFABAINEEBPWNYSBENBURPTRCAYWKCQCNZXWKRWVLVTHJWSOBEWANCJSLRWZOBPNITSTYNTVJJZNCNSPCFDQQNAMMQPVPQWTBPSAMWZECDXXCKBBEQKSKLALCZRZCNFDYOXEAYHHKRNF';

for ( var n = 0; n < 64; i += 1) {
    for ( var i = n; i < 124*64;  i += 64) {
        //console.log(haystack[i]);
        var vertical = vertical + i;
    }
}

console.log(vertical);

But what? I've done other (indexOf) operations on this large string and an equally large array and performance was fine. Is this nested for loop a nasty piece of work? How should I be writing it?

"pegs all 8 cores @100%" weird for a single-threaded program. — djechlin
– djechlin, Commented Jan 14, 2014 at 6:08
That's what I thought. I'm guessing console.log gets a thread for each execution, like async file operations do — Antonius Bloch
– Antonius Bloch, Commented Jan 14, 2014 at 6:26

user229044 · Accepted Answer · 2014-01-14 06:19:42Z

4

This has nothing to do with the string, you're not even accessing it.

You've screwed up your indexing variables, and the loop never terminates. Nowhere do you ever attempt to increment n, so it sits at 0 forever.

answered Jan 14, 2014 at 6:19

user229044♦

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Comments

cyberwombat · Accepted Answer · 2014-01-14 06:35:24Z

0

First line you have 'i' instead of 'n'. Meaning you never leave the outer loop.

for ( var n = 0; n < 64; n += 1) {}

answered Jan 14, 2014 at 6:35

cyberwombat

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