Why is MongoDB's local database almost completely in memory? -

-

i have replicated mongodb setup , seeing lot of page faults. started investigate , found out (through vmmap) entire local database in memory (that is, part of working set). collection of significance there of course oplog.rs used replication. looking @ queries being run, ones on oplog data lot closer tail head of oplog. why entire thing still in memory? surely should swapped out due large amount of faults.

am misunderstanding here? reading vmmap information incorrectly? or going wrong?

vmmap screenshot

note testing setup , there other mongod instances running on hardware, therefore total amount of memory used here not sum total in machine. overall, memory usage ~100% though.

mongo delegates page management kernel - since uses mapped files, relies on kernel decide page out. local database being touched every time write, or receive read another. oplog capped collection, it's going modifying fixed space in data files (and thus, fixed space in ram), should keep touched , not high on priority list being paged out.

as high number of page faults, possible simple cache warming? mongo isn't going load working set memory when it's freshly started, it'll take bit of querying things warm , stuff off of disk , memory.

don't forget account caches , buffers - memory usage might reading @ 100%, kernel going expire caches , buffers before pages out other things, might while system reporting close 100% usage, significant chunk of caches , buffers that'll flushed needed, meaning mongo's working set never has paged out @ all.

you might able test running program designed eat more , more memory (like one) , see how mongo behaves once system hitting swap.


Comments

Post a Comment

Popular posts from this blog

java - Jmockit String final length method mocking Issue -

-
using jmockit 1.2 jar, trying mock string's length method getting unexpected invocation exception: failed: test java.lang.illegalstateexception: missing invocation mocked type @ point; please make sure such invocations appear after declaration of suitable mock field or parameter @ stringdemo.testa$1.<init>(testa.java:17) @ stringdemo.testa.test(testa.java:13) i using testng: @test public void test() throws exception { new expectations() { @mocked("length") string astring; { astring.length(); result = 2; } }; system.out.println(a.showa("test")); } } actual class a: public class { public static int showa(string str){ int a= str.length(); return a; } } this wrong way of recording expected results. shouldn't mock , record string's length() method, record showa() instead. here solution @suppresswarnings("unused...
Read more

What is the difference between data design and data model(ERD) -

-
i have google question , find answer in day. know, data design many many table have list column,and mark pk , fk. why er-diagram have find this? data design process of designing database. main output of data design detailed logical data model of database. some people data design includes of needed logical , physical design choices , physical storage parameters needed generate design in data definition language. technically, database analysis, database analysts (dbas) trained do. while person can both data design , database analysis, these 2 different tasks. data design models data. database analysis takes model , applies 1 or more database engines (relational, hierarchical, nosql). a logical data model 1 of main outputs of data design. data model represented entity relationship diagram, or er diagram.
Read more

ios - Can NSManagedObject conform to NSCoding -

-
i need transfer single object across device. right converting nsmanagedobject dictionary , archiving , sending nsdata. upon receiving unarchiving it. transfer nsmanagedobject archiving , unarchiving instead of creating intermediate data object. @interface test : nsmanagedobject<nscoding> @property (nonatomic, retain) nsstring * title; @end @implementation test @dynamic title; - (id)initwithcoder:(nscoder *)coder { self = [super init]; if (self) { self.title = [coder decodeobjectforkey:@"title"]; //<crash } return self; } - (void)encodewithcoder:(nscoder *)coder { [coder encodeobject:self.title forkey:@"title"]; } @end nsdata *archivedobjects = [nskeyedarchiver archiveddatawithrootobject:testobj]; nsdata *objectsdata = archivedobjects; if ([objectsdata length] > 0) { nsarray *objects = [nskeyedunarchiver unarchiveobjectwithdata:objectsdata]; } the problem above code is. crashes @ self.title in initwithcoder sa...
Read more