mapreduce - Number of reducers in hadoop -

-

i learning hadoop, found number of reducers confusing :

1) number of reducers same number of partitions.

2) number of reducers 0.95 or 1.75 multiplied (no. of nodes) * (no. of maximum containers per node).

3) number of reducers set mapred.reduce.tasks.

4) number of reducers closest to: multiple of block size * task time between 5 , 15 minutes * creates fewest files possible.

i confused, explicitly set number of reducers or done mapreduce program itself?

how number of reducers calculated? please tell me how calculate number of reducers.

1 - number of reducers number of partitions - false. single reducer might work on 1 or more partitions. chosen partition done on reducer started.

2 - theoretical number of maximum reducers can configure hadoop cluster. dependent on kind of data processing (decides how heavy lifting reducers burdened with).

3 - mapred-site.xml configuration suggestion yarn. internally resourcemanager has own algorithm running, optimizing things on go. value not number of reducer tasks running every time.

4 - 1 seems bit unrealistic. block size might 128mb , everytime can't have 128*5 minimum number of reducers. that's again false, believe.

there no fixed number of reducers task can configured or calculated. depends on moment how of resources available allocate.


Comments

Post a Comment

Popular posts from this blog

java - Static nested class instance -

-
this question has answer here: java inner class , static nested class 23 answers i came across in java, know static nested class why create instance of 'static'. isn't whole idea of 'static' use without instance? understand concept of inner classes, why (and frankly how possible to) create 'instance' of 'static' member @ ? why this: 1- outerclass.staticnestedclass nestedobject = new outerclass.staticnestedclass(); 2- nestedobject.anestedclassmethod(); and not this: 1- outerclass outerinstance=new outerclass(); 2- outerinstance.staticnestedclass.anestedclassmethod(); use on inner classes, keyword static indicates can access inner class without instance of outer class. for example: public class outer { public static class inner { /* code here. */ } } with construction, can create instance of inn
Read more

c# - Bluetooth LE CanUpdate Characteristic property -

-
i building xamarin.forms cross platform mobile app, uses monkey.robotics bluetoth low energy functionality. connecting mbed based implimentation of custom gatt service . in xamarin c#, triggers characteristic. canupdate property in monkey.robotics? this standard example c# based on: if (characteristic.canupdate) { characteristic.valueupdated += (s, e) => { debug.writeline("characteristic.valueupdated"); device.begininvokeonmainthread( () => { updatedisplay(characteristic); }); isbusy = false; // spin until first result received }; isbusy = true; characteristic.startupdates(); } this has been working, since changed own custom gatt service connecting to, canupdate property false. property , how triggered? me debugging gatt service code. thanks monkey.robotics open sour
Read more

JavaScript - Replace variable from string in all occurrences -

-
ok, know if have character '-' , want remove in places in string javascript, ... someword = someword.replace(/-/g, ''); but, when applying array of characters, s not working ... const badchars = ('\/:*?"<>|').split(''); let filename = title.replace(/ /g, '-').tolocalelowercase(); (let item = 0; item < badchars.length; item++) { // below not work global '/ /g' filename = filename.replace(/badchars[item]/g, ''); } any ideas? /badchars[item]/g looks badchars , literally, followed i , t , e , or m . if you're trying use character badchars[item] , you'll need use regexp constructor, , you'll need escape regex-specific characters. escaping regular expression has been well-covered . using that: filename = filename.replace(new regexp(regexp.quote(badchars[item]), 'g'), ''); but , don't want that. want character class: let filename = title.replac
Read more