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?
You have to set "secondary 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.secondaryOk()
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 secondaryOk when querying from secondaries, and only once per session.
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.
in mongodb2.0
you should type
rs.slaveOk()
in secondary mongod node
THIS IS JUST A NOTE FOR ANYONE DEALING WITH THIS PROBLEM USING THE RUBY DRIVER
I had this same problem when using the Ruby Gem.
To set slaveOk in Ruby, you just pass it as an argument when you create the client like this:
mongo_client = MongoClient.new("localhost", 27017, { slave_ok: true })
https://github.com/mongodb/mongo-ruby-driver/wiki/Tutorial#making-a-connection
mongo_client = MongoClient.new # (optional host/port args)
Notice that 'args' is the third optional argument.
WARNING: slaveOk() is deprecated and may be removed in the next major release. Please use secondaryOk() instead. rs.secondaryOk()
I got here searching for the same error, but from Node.js native driver. The answer for me was combination of answers by campeterson and Prabhat.
The issue is that readPreference setting defaults to primary, which then somehow leads to the confusing slaveOk error. My problem is that I just wan to read from my replica set from any node. I don't even connect to it as to replicaset. I just connect to any node to read from it.
Setting readPreference to primaryPreferred (or better to the ReadPreference.PRIMARY_PREFERRED constant) solved it for me. Just pass it as an option to MongoClient.connect() or to client.db() or to any find(), aggregate() or other function.
https://docs.mongodb.com/v3.0/reference/read-preference/#primaryPreferred
http://mongodb.github.io/node-mongodb-native/3.6/api/Collection.html (search readPreference)
const { MongoClient, ReadPreference } = require('mongodb');
const client = await MongoClient.connect(MONGODB_CONNECTIONSTRING, { readPreference: ReadPreference.PRIMARY_PREFERRED });
slaveOk does not work anymore. One needs to use readPreference https://docs.mongodb.com/v3.0/reference/read-preference/#primaryPreferred
e.g.
const client = new MongoClient(mongoURL + "?readPreference=primaryPreferred", { useUnifiedTopology: true, useNewUrlParser: true });
I am just adding this answer for an awkward situation from DB provider.
what happened in our case is the primary and secondary db shifted reversely (primary to secondary and vice versa) and we are getting the same error.
so please check in the configuration settings for database status which may help you.
Adding readPreference as PRIMARY
const { MongoClient, ReadPreference } = require('mongodb');
const client = new MongoClient(url, { readPreference: ReadPreference.PRIMARY_PREFERRED});
client.connect();
I want to know that is it useful to opan a connection inside parenthesis of try cause at the end there is no need to close that connection it happens automatically..... ?
The value of defining a connection within a using statement is that the variable defined is automatically disposed at the end of the block. It is still good practice to explicitly Close() the connection when you're done using it. Like this in SQL Server:
using(var conn = new SqlConnection(...)) {
...
conn.Close();
}
At the end of the using() block, conn.Dispose() is called automatically even if an exception occurs within the block.
Somewhere in my Vaadin application, I'm getting this exception as soon as I connect using a second browser
Caused by: java.lang.RuntimeException: A connector with id 22 is already registered!
at com.vaadin.ui.ConnectorTracker.registerConnector(ConnectorTracker.java:133)
It happens always in the same place but I don't know why exactly as the reason for this must be somewhere else.
I think I might be stealing UI components from the other session - which is not my intention.
Currently, I don't see any static instances of UI components I might be using in multiple sessions.
How can I debug this? It's become quite a large project.
Any hints to look for?
Yes, this usually happens because you are attaching a component already attached in other session.
Try logging the failed connector with a temporal ConnectorTracker, So the next time that it happens, you can catch it.
For example:
public class SomeUI extends UI {
private ConnectorTracker tracker;
#Override
public ConnectorTracker getConnectorTracker() {
if (this.tracker == null) {
this.tracker = new ConnectorTracker(this) {
#Override
public void registerConnector(ClientConnector connector) {
try {
super.registerConnector(connector);
} catch (RuntimeException e) {
getLogger().log(Level.SEVERE, "Failed connector: {0}", connector.getClass().getSimpleName());
throw e;
}
}
};
}
return tracker;
}
}
I think I might be stealing UI components from the other session - which is not my intention. Currently, I don't see any static instances of UI components I might be using in multiple sessions.
That was it. I was actually stealing UI components without prior knowledge.
It was very well hidden in a part which seems to be same for all instances. Which is true: the algorithm is the same.
Doesn't mean I should've reused the same UI components as well...
Thanks to those who took a closer look.
Here is how I fixed it -
1) look for components you have shared across sessions. For example if you have declared a component as static it will be created once and will be shared.
2) if you are not able to find it and want a work around until you figure out the real problem, put your all addComponent calls in try and in catch add following code -
getUI().getConnectorTracker().markAllConnectorsDirty();
getUI().getConnectorTracker().markAllClientSidesUnititialized();
getPage().reload():
This will clear old connectors and will reload the page properly only when it fails. For me it was failing when I was logged out and logged in back.
Once you find the real problem you can fix it till then inform your customers about the reload.
**** note - only solution is to remove shared components this is just a work around.
By running your application in debug mode (add ?debug at the end of URL in browser) you will be able to browse to the component, e.g:
-UIConnector(0)
--VerticalLayoutConnector(1)
---...
---LabelConnector(22)
where 22 is id from your stack trace. Find this component in your code and make sure that it is not static (yes, I saw such examples).
I get this error when I run mysql_real_escape_string($value).
Warning: mysql_real_escape_string() [function.mysql-real-escape-string]: Can't connect to MySQL server on 'localhost' (10061) in ...
I wrapped up the functionality in a nice class like this
class escaper
{
function __get($value)
{
//in order for this to work properly, I must have a live connection to mysql
return mysql_real_escape_string($value);
}
}
/*
//sample usage
$safe = new escaper;
$name = "O'Reilly";
echo $safe->$name
In case someone goes down that road again, let me say it upfront that Yes! I should use PDO and parametrized queries and that the above method is not that safe.
how do you programmatically tell whether a mysql connection is present?
we just don't need that.
connection is always present
Escaping being a part of the DB class.
Connect to the database is the very first thing this class doing in the constructor.
And connect resource stored in the class variable.
So, only we need is to use this variable - easy-peasy.
OK, I'm trying to set a property on a type I'm registering with SM.
Here's the code from the registry in one of my components. This
registry is being added during the configuration from a console app.
When I try to access the EndorsementSpecs property of the instance
AutoMandatoryEndorsementAggregator object, I get the 202. What's
interesting is that I can call
GetAllInstances>() from my
console app and it resolves just fine. Is there something about
accessing this code from within OnCreation that is causing the 202? I
can see everything I expect in WhatDoIHave(). I've also tried a TypeInterceptor with the same results.
//register all open generics
cfg.ConnectImplementationsToTypesClosing(typeof
(MandatoryEndorsementSpecBase<>));
ForSingletonOf<IMandatoryEndorsementAggregator<AutoPolicy>>()
.Use<AutoMandatoryEndorsementAggregator>()
.OnCreation((context, x) =>
{
var specs =
context.GetAllInstances<MandatoryEndorsementSpecBase<AutoPolicy>>();
x.EndorsementSpecs = specs;
})
;
Sorry to deflect your real questions, but are you just trying to inject all instances of MandatoryEndorsementSpecBase into AutoMandatoryEndorsementAggregatory?
If so, you can probably get away with just making it a constructor parameter so that they are all automatically injected.
public AutoMandatoryEndorsementAggregatory(MandatoryEndorsementSpecBase<AutoPolicy>[] endorsementSpecs){
EndorsementSpecs = endorsementSpecs;
}