Homework: Homework 6.4


You have a sharded system with three shards and have sharded the collections “students” in the “school” database across those shards. The output of sh.status() when connected to mongos looks like this:

mongos> sh.status()
--- Sharding Status --- 
  sharding version: {
	"_id" : 1,
	"minCompatibleVersion" : 5,
	"currentVersion" : 6,
	"clusterId" : ObjectId("5531512ac723271f602db407")
}
  shards:
	{  "_id" : "s0",  "host" : "s0/localhost:37017,localhost:37018,localhost:37019" }
	{  "_id" : "s1",  "host" : "s1/localhost:47017,localhost:47018,localhost:47019" }
	{  "_id" : "s2",  "host" : "s2/localhost:57017,localhost:57018,localhost:57019" }
  balancer:
	Currently enabled:  yes
	Currently running:  yes
		Balancer lock taken at Fri Apr 17 2015 14:32:02 GMT-0400 (EDT) by education-iMac-2.local:27017:1429295401:16807:Balancer:1622650073
	Collections with active migrations: 
		school.students started at Fri Apr 17 2015 14:32:03 GMT-0400 (EDT)
	Failed balancer rounds in last 5 attempts:  0
	Migration Results for the last 24 hours: 
		2 : Success
		1 : Failed with error 'migration already in progress', from s0 to s1
  databases:
	{  "_id" : "admin",  "partitioned" : false,  "primary" : "config" }
	{  "_id" : "school",  "partitioned" : true,  "primary" : "s0" }
		school.students
			shard key: { "student_id" : 1 }
			chunks:
				s0	1
				s1	3
				s2	1
			{ "student_id" : { "$minKey" : 1 } } -->> { "student_id" : 0 } on : s2 Timestamp(3, 0) 
			{ "student_id" : 0 } -->> { "student_id" : 2 } on : s0 Timestamp(3, 1) 
			{ "student_id" : 2 } -->> { "student_id" : 3497 } on : s1 Timestamp(3, 2) 
			{ "student_id" : 3497 } -->> { "student_id" : 7778 } on : s1 Timestamp(3, 3) 
			{ "student_id" : 7778 } -->> { "student_id" : { "$maxKey" : 1 } } on : s1 Timestamp(3, 4) 


If you ran the query

use school
db.students.find({'student_id':2000})

Which shards would be involved in answering the query?

tthw6.4answer

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