10

I tried mongo replica sets for the first time.

I am using ubuntu on ec2 and I booted up three instances. I used the private IP address of each of the instances. I picked on as the primary and below is the code.

mongo --host Private IP Address
rs.initiate()
rs.add(“Private IP Address”)
rs.addArb(“Private IP Address”)

All at this point is fine. When I go to the http://ec2-xxx-xxx-xxx-xxx.compute-1.amazonaws.com:28017/_replSet site I see that I have a primary, seconday, and arbitor.

Ok, now for a test.

On the primary create a database in this is the code:

use tt
db.tt.save( { a : 123 } )

on the secondary, I then do this and get the below error:

db.tt.find()
error: { "$err" : "not master and slaveOk=false", "code" : 13435 }

I am very new to mongodb and replicates but I thought that if I do something in one, it goes to the other. So, if I add a record in one, what do I have to do to replicate across machines?

edited May 31 '13 at 3:15

eLRuLL
1,02121127

asked Jan 24 '12 at 16:14

user959129

figured out that I have to use rs.slaveOk(); That leaves me to another question. I have to do this do this for every query? What if I am on the master node? – user959129 Jan 24 '12 at 16:26

add comment

4 Answers

active oldest votes

up vote 59 down vote

You have to set "slave okay" mode to let the mongo shell know that you're allowing reads from a secondary. This is to protect you and your applications from performing eventually consistent reads by accident. You can do this in the shell with:

rs.slaveOk()

After that you can query normally from secondaries.

A note about "eventual consistency": under normal circumstances, replica set secondaries have all the same data as primaries within a second or less. Under very high load, data that you've written to the primary may take a while to replicate to the secondaries. This is known as "replica lag", and reading from a lagging secondary is known as an "eventually consistent" read, because, while the newly written data will show up at some point (barring network failures, etc), it may not be immediately available.

Edit: You only need to set slaveok when querying from secondaries, and only once per session.

answered Jan 24 '12 at 16:30

dcrosta
10.9k22646

add comment

up vote 6 down vote

To avoid typing rs.slaveOk() every time, do this:

Create a file named replStart.js, containing one line: rs.slaveOk()

Then include --shell replStart.js when you launch the Mongo shell. Of course, if you're connecting locally to a single instance, this doesn't save any typing.

answered Mar 25 '13 at 19:54

Ed Norris
6911018

5

A better way to save on typing would be to add rs.slaveOk() to your ~/.mongorc.js file, which will be automatically executed when starting the mongo shell. – Stennie May 7 '13 at 14:27

1

I find it useful to put the default configuration in ~/.mongorc.js and custom configurations in replStart.js or adminStart.js or whatever. – Ed Norris May 13 '13 at 17:58

add comment

up vote 3 down vote

in mongodb2.0

you should type

rs.slaveOk

in primary mongod node

answered Feb 29 '12 at 8:50

andyshi
28027

add comment

come from :http://stackoverflow.com/questions/8990158/mongodb-replicates-and-error-err-not-master-and-slaveok-false-code

ITPub博客

mongodb,“not master and slaveOk=false”

4 Answers

最新文章