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?
Answer: s1
