Adjust Priority for Replica Set Member¶

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Overview
Considerations
Procedure

Overview¶

The priority settings of replica set members affect the outcomes of elections for primary. Use this setting to ensure that some members are more likely to become primary and that others can never become primary.

The value of the member’s members[n].priority setting determines the member’s priority in elections. The higher the number, the higher the priority.

Considerations¶

To modify priorities, you update the members array in the replica configuration object. The array index begins with 0. Do not confuse this index value with the value of the replica set member’s members[n]._id field in the array.

The value of members[n].priority can be any floating point (i.e. decimal) number between 0 and 1000. The default value for the members[n].priority field is 1.

To block a member from seeking election as primary, assign it a priority of 0. Hidden members, delayed members, and arbiters all have members[n].priority set to 0.

Adjust priority during a scheduled maintenance window. Reconfiguring priority can force the current primary to step down, leading to an election. Before an election the primary closes all open client connections.

Procedure¶

1

Copy the replica set configuration to a variable.¶

In the mongo shell, use rs.conf() to retrieve the replica set configuration and assign it to a variable. For example:

cfg = rs.conf()

2

Change each member’s priority value.¶

Change each member’s members[n].priority value, as configured in the members array.

cfg.members[0].priority = 0.5
cfg.members[1].priority = 2
cfg.members[2].priority = 2

This sequence of operations modifies the value of cfg to set the priority for the first three members defined in the members array.

3

Assign the replica set the new configuration.¶

Use rs.reconfig() to apply the new configuration.

rs.reconfig(cfg)

This operation updates the configuration of the replica set using the configuration defined by the value of cfg.

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