1

I have a 3 members replica set version 2.6.1 with following configuration

                    "_id" : 0,
                    "host" : "10.125.16.22:30000",
                    "priority" : 2

                    "_id" : 1,
                    "host" : "10.125.16.22:40000"

                    "_id" : 2,
                    "host" : "10.125.16.22:60000",
                    "priority" : 0,
                    "slaveDelay" : 3600,
                    "hidden" : true

And i want id:2 to sync from id:1.

I execute

db.adminCommand( { replSetSyncFrom: "10.125.16.22:40000" } ) 

and got

"syncFromRequested" : "10.125.16.22:40000",
"prevSyncTarget" : "10.125.16.22:30000",
"ok" : 1

But on rs.status the sync is still syncingTo : "10.125.16.22:30000"

I found on documentation:

Changed in version 2.4: The sync target falls more than 30 seconds behind another member of the replica set; the mongod will revert to the default sync target.

Is this what happened in my case? if yes is there any workaround?

1

There isn't enough information here to know if the "sync target falling more than 30s behind" was the case, but it seems likely if you are pushing through a lot of activity with all of your replica set nodes on the same machine.

There should be some log entries confirming the change; if you're still on 2.6 you should be able to grep for:

 changing sync target because current sync target's most recent OpTime is

One thing to note is that rs.syncFrom() is a temporary change. By default the sync targets are automatically chosen by MongoDB, and will be reset if you restart instances or lose connectivity.

There's a helpful open source tool called Edda which you can use to process MongoDB log files and visualise changes in replica set history. NOTE: The github repository has changed since that blog post was published; the current repo is 10gen-labs/edda.

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