Mongo sync: slow down or stop sync? - mongodb

Question

All,
I have a replicaset setup where I run two mongo processes, M_pri on port 28001 and M_sec on 28002 in the same machine with the following config:
"_id" : "myReplSet",
"version" : 1,
"protocolVersion" : NumberLong(1),
"members" : [
{
"_id" : 0,
"host" : "localhost:28001",
"arbiterOnly" : false,
"buildIndexes" : true,
"hidden" : false,
"priority" : 1,
"slaveDelay" : NumberLong(0),
"votes" : 1
},
{
"_id" : 1,
"host" : "localhost:28002",
"arbiterOnly" : false,
"buildIndexes" : true,
"hidden" : true,
"priority" : 0,
"slaveDelay" : NumberLong(0),
"votes" : 1
}
],
"settings" : {
"chainingAllowed" : true,
"heartbeatIntervalMillis" : 2000,
"heartbeatTimeoutSecs" : 10,
"electionTimeoutMillis" : 10000,
"catchUpTimeoutMillis" : 2000,
"getLastErrorModes" : {
},
"replicaSetId" : ObjectId("593565b0ebd8ca36a07c6576")
}
The intention for this setup is to take a daily mongodump (gunzip) off M_sec. During the mongodump the whole of my system slow down as I have these processes that make writes and reads off the M_pri.
Is there a way by which I could stop the sync from Primary to Secondary mongo during the time when I am doing a mongodump off M_sec?
Thanks

Answer 1

You can set the M_sec to be a delayed member (https://docs.mongodb.com/manual/core/replica-set-delayed-member/#replica-set-delayed-members), so it will replicate from M_pri with a delay.
Things to keep in mind:
Requirements
Delayed members:
Must be priority 0 members. Set the priority to 0 to prevent a delayed member from becoming primary.
Should be hidden members. Always prevent applications from seeing and
querying delayed members.
do vote in elections for primary, if members[n].votes is set to 1.
Behavior
Delayed members copy and apply operations from the source oplog on a
delay. When choosing the amount of delay, consider that the amount of
delay:
must be equal to or greater than your expected maintenance window durations.
must be smaller than the capacity of the oplog. For more information on oplog size, see Oplog Size.
Configuration example:
{
"_id" : <num>,
"host" : <hostname:port>,
"priority" : 0,
"slaveDelay" : <seconds>,
"hidden" : true
}