Final 1
-------
Answer: 9
Final 2
-------
Answer: 2
Mongo preserves the order of writes in a collection in its consistency model. In this problem, 27003's oplog was effectively a "fork" and to preserve write ordering a rollback was necessary during 27003's recovery phase.
Final 3
-------
3 documents
> bsondump test.foo.2013-03-11T10-25-48.0.bson
{ "_id" : 7 }
{ "_id" : 8 }
{ "_id" : 9 }
3 objects found
Final 4
--------
z:PRIMARY> cfg = rs.conf()
z:PRIMARY> cfg.members[2].votes = 0
z:PRIMARY> cfg
{
"_id" : "z",
"version" : 1,
"members" : [
{
"_id" : 1,
"host" : "localhost:27001"
},
{
"_id" : 2,
"host" : "localhost:27002"
},
{
"_id" : 3,
"host" : "localhost:27003",
"votes" : 0
}
]
}
z:PRIMARY> rs.reconfig(cfg)
{ "ok" : 1 }
~% mongo --shell a.js --port 27003
z:SECONDARY> part4()
233
Answer: 233
Final 5
-------
z:PRIMARY> a = {_id : 1,
author : 'joe',
title : 'Too big to fail',
text : 'Sample text',
tags : [ 'business', 'finance' ],
when : ISODate("2008-11-03"),
views : 23002,
votes : 4,
voters : ['joe', 'jane', 'bob', 'somesh'],
comments : [
{ commenter : 'allan',
comment : 'Well, i dont think so…',
flagged:false, plus:2 },
{ commenter : 'chuck',
comment : 'where is',
flagged:true, plus:5 },
{ commenter : 'norris',
comment : 'my leg',
flagged:true, plus:77777777 },
]
}
z:PRIMARY> db.postings.insert(a)
One way to assure people vote at most once per posting is to use this form of update:
db.postings.update(
{ _id:… , voters:{$ne:'joe'} },
{ $inc : {votes:1}, $push : {voters:'joe'} } );
Answer: db.postings.find( { "comments.flagged" : true } )
db.postings.update(
{ _id:… , voters:{$ne:'joe'} },
{ $inc : {votes:1}, $push : {voters:'joe'} } );
Final 6
-------
MongoDB supports atomic operations on individual documents.
MongoDB has a data type for Dates and DateTime data.
Answer: 2 & 4
Final 7
-------
MongoDB supports reads from slaves/secondaries that are in remote locations.
Answer: 2
Final 8
-------
mkdir ./data
mkdir ./data/configdb
mongod --configsvr --dbpath ./data/configdb --port 27019
mongorestore ./config_server --host 127.0.0.1:27019
~%/Documents/Mongo/dba/final.8$
~%/Documents/Mongo/dba/final.8$ mongo localhost:27019/config
MongoDB shell version: 2.2.2
connecting to: localhost:27018/config
configsvr>
configsvr> db
config
configsvr> db.chunks.find().sort({_id:1}).next().lastmodEpoch.toString().substr(20,4)
6554
configsvr> ^C
bye
~%/Documents/Mongo/dba/final.8$
> configsvr> db.chunks.find().sort({_id:1}).next().lastmodEpoch.getTimestamp().toString().substr(19,5)
> 07:07
Answer: 07:07
Final 9
-------
mongorestore --oplogReplay s1 --host SPHINX --port 27017
mongorestore --oplogReplay s2 --host SPHINX --port 27017
-- Update shards
>db.shards.update({"_id":"s1"},{$set : {"host":"localhost:27501"}})
>db.shards.update({"_id":"s2"},{$set : {"host":"localhost:27601"}})
configsvr> db.shards.find()
{ "_id" : "s1", "host" : "localhost:27501" }
{ "_id" : "s2", "host" : "localhost:27601" }
-- Run des deux shards
-- FAUX mongod --shardsvr --port 27501 --fork --logpath s1.log --replSet s1
-- FAUX mongod --shardsvr --port 27601 --fork --logpath s2.log --replSet s2
-- Pas de RS à préciser
>mongod --shardsvr --port 27501 --fork --logpath s1.log
> (remove /data/db/mongo.lock si besoin)
>mongod --shardsvr --port 27601 --fork --logpath s2.log
mongos> use snps
switched to db snps
mongos> db.elegans.aggregate([{$match:{N2:"T"}},{$group:{_id:"$N2",n:{$sum:1}}}]).result[0].n
47664
Final 10
--------
mongos> db.elegans.ensureIndex({"N2":1,"mutant":1})
removed == 1 + _files.size()
mongos>
Answer: 2 shards are queried.
10 documents are scanned.