Forcing connection to a local mongos + verbose logging that specifies

[Guillaume Forget]

Hello,

We are using MongoDB for a Java web app running on Amazon EC2 machines across 3 availability zones (AZ). On each machine, we have one Java VM and one mongos. When initializing the connection to Mongo, we specify localhost and 3 other machines (possibly the local one) that are located in different AZs for failover scenarios. Once in a while I will see a read timeout specifying a mongos that isn't the one running locally. Ideally I'd like to force the connection to the local mongos unless it's dead. Is it possible? The javadoc for the Java driver indicates that the driver will pick the host with the lowest ping time. I have a hard time to believe that this will not be the localhost one.

Also, is it possible to turn on some logging which will print out the query being sent and which server it was sent to? I looked at the source code of the Java driver but didn't see anything.

Thanks

Gui

[Jeff Yemin]

Yes, it's a bit strange, but the selection of a mongos with lowest ping time is "sticky", so if it happens that randomly the local mongos doesn't have the fastest ping time right at startup, the driver will stick to one of the non-local ones.

The driver doesn't log every query currently, so your best bet is to use the server logs to monitor.

There are a couple of related Jira issues that you can watch:

https://jira.mongodb.org/browse/JAVA-374

https://jira.mongodb.org/browse/JAVA-699

Regards,

Jeff

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[Guillaume Forget]

Hey Jeff,

Thanks for the response. I wasn't so much "complaining" about the stickiness but rather the fact that if I specify multiple mongos addresses, I don't get to specify a preferred one which in my case would be localhost.

And on the same topic, I'm very confused with the following behavior:  I'm initializing the Mongo instance (Java object) with the following options:

2013-10-24 21:30:35,906 [http-8080-exec-6] INFO  Mongo{authority=MongoAuthority{type=Set, serverAddresses=[localhost/127.0.0.1:27027, HOST1/10.149.12.79:27027, HOST2/10.154.149.70:27027, HOST3/10.158.33.16:27027], credentials={credentials={}}}, options=MongoOptions{description='null', connectionsPerHost=40, threadsAllowedToBlockForConnectionMultiplier=5, maxWaitTime=10000, connectTimeout=10000, socketTimeout=30000, socketKeepAlive=false, autoConnectRetry=false, maxAutoConnectRetryTime=0, slaveOk=false, readPreference=secondaryPreferred : { "tags" : [ { "aws-az" : "us-east-1e"}]}, dbDecoderFactory=DefaultDBDecoder.DefaultFactory, dbEncoderFactory=DefaultDBEncoder.DefaultFactory, safe=false, w=0, wtimeout=0, fsync=false, j=false, socketFactory=javax.net.DefaultSocketFactory@20c66135, cursorFinalizerEnabled=true, writeConcern=WriteConcern { "getlasterror" : 1} / (Continue Inserting on Errors? false), alwaysUseMBeans=false}}

HOST1, HOST2 and HOST3 are dead when I start due to a bad config. And I get the following error:

com.mongodb.MongoException: can't find a master

        at com.mongodb.DBTCPConnector.checkMaster(DBTCPConnector.java:517)

        at com.mongodb.DBTCPConnector.say(DBTCPConnector.java:134)

        at com.mongodb.DBTCPConnector.say(DBTCPConnector.java:115)

        at com.mongodb.DBApiLayer$MyCollection.insert(DBApiLayer.java:248)

If I start with the following options:

2013-10-24 21:43:13,608 [http-8080-exec-19] INFO  Mongo{authority=MongoAuthority{type=Set, serverAddresses=[localhost/127.0.0.1:27027], credentials={credentials={}}}, options=MongoOptions{description='null', connectionsPerHost=40, threadsAllowedToBlockForConnectionMultiplier=5, maxWaitTime=10000, connectTimeout=10000, socketTimeout=30000, socketKeepAlive=false, autoConnectRetry=false, maxAutoConnectRetryTime=0, slaveOk=false, readPreference=secondaryPreferred : { "tags" : [ { "aws-az" : "us-east-1e"}]}, dbDecoderFactory=DefaultDBDecoder.DefaultFactory, dbEncoderFactory=DefaultDBEncoder.DefaultFactory, safe=false, w=0, wtimeout=0, fsync=false, j=false, socketFactory=javax.net.DefaultSocketFactory@2cc29d3d, cursorFinalizerEnabled=true, writeConcern=WriteConcern { "getlasterror" : 1} / (Continue Inserting on Errors? false), alwaysUseMBeans=false}}

Then it starts fine. It's as if it ignored the localhost entry in the first case. I can reproduce this at will. Is this a bug or am I missing something?

Gui

[Jeff Yemin]

Hi Gui,

This is not the behavior that I expect.  Would you mind opening a JIRA issue?

Regards,

Jeff