Choose optimal data structures

Select data structures based on specific access patterns and performance requirements. When both fast lookup and predictable iteration order are needed, specialized structures like IndexMap offer benefits over standard HashMap:

// When order matters and lookups are frequent:
use indexmap::IndexMap;

// Fast lookups + preserved insertion order
let cache: IndexMap<String, CacheColumn> = IndexMap::new();

// Regular HashMap when only lookup speed matters
let simple_lookup: HashMap<String, Value> = HashMap::new();

For serialization, separate concerns from runtime efficiency - use simple Vector structures for serialization, then transform into Maps for runtime lookups. This avoids serializing complex key structures while maintaining fast access patterns:

// For serialization - simple Vec
let serializable_data: Vec<Item> = items.into_iter().collect();

// For runtime - efficient HashMap
let lookup_map: HashMap<ItemId, Item> = 
    serializable_data.into_iter()
                    .map(|item| (item.id, item))
                    .collect();

When implementing caches, consider using reference-based APIs like entry_ref from hashbrown to avoid unnecessary cloning:

use hashbrown::HashMap;

// Avoids cloning the key for lookup
map.entry_ref(key_reference).or_insert_with(|| create_value());

Document your data structure choices to explain performance tradeoffs, especially when choosing specialized structures over standard library alternatives.