How to avoid nested map allocations in my data structure? - dictionary

Question

I have a below struct where I have a nested map for CustomersIndex which allocates bunch of internal maps causing memory increase. I profiled it so I noticed this. I am trying to see if there is any way to redesign my CustomersIndex data structure which doesn't uses nested map?
const (
departmentsKey = "departments"
)
type CustomerManifest struct {
Customers []definitions.Customer
CustomersIndex map[int]map[int]definitions.Customer
}
This is the way it is being populated here in my below code:
func updateData(mdmCache *mdm.Cache) map[string]interface{} {
memCache := mdmCache.MemCache()
var customers []definitions.Customer
var customersIndex = map[int]map[int]definitions.Customer{}
for _, r := range memCache.Customer {
customer := definitions.Customer{
Id: int(r.Id),
SetId: int(r.DepartmentSetId),
}
customers = append(customers, customer)
_, yes := customersIndex[customer.SetId]
if !yes {
customersIndex[customer.SetId] = make(map[int]definitions.Customer)
}
customersIndex[customer.SetId][customer.Id] = customer
}
return map[string]interface{}{
departmentsKey: &CustomerManifest{Customers: customers, CustomersIndex: customersIndex},
}
}
And this is the way I am getting my CustomersIndex nested map.
func (c *Client) GetCustomerIndex() map[int]map[int]definitions.Customer {
c.mutex.RLock()
defer c.mutex.RUnlock()
customersIndex := c.data[departmentsKey].(*CustomerManifest).CustomersIndex
return customersIndex
}
Is there any way to design my CustomersIndex in a way where I don't have to use nested map?

Answer 1

You don't need to allocate a map until you put values in it.
type CustomerManifest struct {
Customers []definitions.Customer
CustomersIndex map[int]map[int]definitions.Customer
}
func (m *CustomerManifest) AddCustomerDefinition(x, y int, customer definitions.Customer) {
// Get the existing map, if exists.
innerMap := m.CustomersIndex[x]
// If it doesn't exist, allocate it.
if innerMap == nil {
innerMap = make(map[int]definitions.Customer)
m.CustomersIndex[x] = innerMap
}
// Add the value to the inner map, which now exists.
innerMap[y] = customer
}