Database Reference
In-Depth Information
Different forms of secondary members
The secondary members can be defined for various purposes by changing the default mem-
ber's configuration. A secondary member can be configured to the following:
• The priority 0 member.
• The hidden member.
• The delayed member.
• To design an efficient replica set, each type of member becomes handy in some
cases. In next parts of the chapter, you can read the purpose of each kind of the
aforementioned secondary members.
Using the priority 0 member
Although these kinds of members cannot become primary, they function as normal second-
ary members. This means that the priority 0 members contains the same dataset as a
primary
node, accepts read operations, and also votes in the election process.
Note
Members have priority equal to 1 by default.
The following diagram shows you a replica set with three members: one
primary
node,
and two
secondary
nodes. The first
secondary
node (the green box) can become
primary
, but the second
secondary
node (the gray box) can't change its state because
it's a priority 0 member. This is shown in the following diagram:
Also, a priority 0 member can be hosted in a dedicated machine. The following diagram il-
lustrates this case:
