database - DBInputFormat multiple records processing -

-

when connect rdbms mysql using hadoop record db user-defined class extends dbwritable , writable. if our sql query generates n records output act of reading record user-defined class done n times. there way in can more number of records mapper @ same time instead of 1 record each time ?

if understand correctly, think hadoop causes n select statements under hood. not true. can see in dbinputformat's source, creates chunks of rows based on hadoop deems fit.

obviously, each mapper have execute query fetch data process, , might repeatedly, that's still near number of rows in table.

however, if performance degrades, might better off dumping data hdfs / hive , processing there.


Comments

Post a Comment

Popular posts from this blog

Delphi XE2 Indy10 udp client-server interchange using SendBuffer-ReceiveBuffer -

-
i use delphi xe2 , indy10 udp protocol. can't receive server echo on client side if use receivebuffer method. got "socket error # 10040" although send small echo message server client. console application illustrate problem below. in advance. program project1; {$apptype console} {$r *.res} uses system.sysutils, idglobal, idbasecomponent, idcomponent, idsockethandle, idudpclient, idudpserver, idudpbase, idstack; type tudp_serv = class(tidudpserver) procedure udpsvudpread(athread: tidudplistenerthread; adata: tidbytes; abinding: tidsockethandle); end; var udpserver: tudp_serv; udpcl: tidudpclient; bsnd, brcv: tbytes; s: string; k: integer; //============================================================================== procedure tudp_serv.udpsvudpread(athread: tidudplistenerthread; adata: tidbytes; abinding: tidsockethandle); begin writeln(' server read: ' + tohex(adata, length(adata))); abinding sendto(peerip, peerport, adat...
Read more

Qt ActiveX WMI QAxBase::dynamicCallHelper: ItemIndex(int): No such property in -

-
i new windows programming. here goes code objiwbemlocator = new qaxobject("wbemscripting.swbemlocator"); objwmiservice = objiwbemlocator->querysubobject("connectserver(qstring&,qstring&)",qstring("."),qstring("root\\cimv2")); qaxobject* returnlist = objwmiservice->querysubobject("execquery(qstring&)", qstring("select * %1").arg(domain)); qaxobject* result = returnlist->querysubobject("itemindex(int)", 0); i getting error on runtime qt activex wmi qaxbase::dynamiccallhelper: itemindex(int): no such property in but itemindex method exists msdn says the itemindex method not work collections not contain swbemobjects, such swbemmethodset, swbemnamedvalueset, swbemprivilegeset, swbempropertyset, , swbemqualifierset. what selecting ? have tried iterating on collection ? plus need minimum windows vista itemindex method. hope helps
Read more

Enable autocomplete or intellisense in Atom editor for PHP -

-
i'm first time user of atom editor php code. atom can autocomplete built-in functions of php. possible make editor autocomplete custom function written in separate file? function.php <?php function printsomething() { echo "hello world"; } index.php <?php require_once "function.php"; printsomething(); // autocompleted atom editor while typing thanks in advance. there text file in %userprofile%.atom called snippets.cson. in there can add snippet. more this: http://flight-manual.atom.io/using-atom/sections/snippets/ but need think can use later on other files well. otherwise need copy , paste.
Read more