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- CPU-Intensive Operations
- Memory Leaks
- Inefficient Algorithms
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- Inefficient Data Structures
- Excessive Object Creation
- Synchronization Issues
- I/O Bottlenecks
- String Manipulation
- Inefficient Loops
- Lazy Loading Issues
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- UI Rendering Bottlenecks
- Serialization Overhead
- Logging overhead
- Reflection misuse
- Thread pool issues
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Enterprise
Inefficient Data Structures
Anti-patterns related to data structure selection and usage that can lead to performance issues.
Choosing the right data structure for a specific operation is crucial for application performance. Using inappropriate data structures can lead to excessive CPU usage, memory consumption, and poor scalability, especially when dealing with large datasets or frequent operations.
Common data structure inefficiencies include:
- Using the wrong collection type for specific operations
- Inefficient access patterns
- Unnecessary data copying
- Poor memory locality
- Excessive boxing/unboxing
This guide covers common anti-patterns related to data structure selection and usage, along with best practices for optimizing performance across different programming languages and application types.
// Anti-pattern: Using ArrayList for frequent insertions at arbitrary positions
public void processTasksInefficiently(List<Task> tasks) {
List<Task> processingQueue = new ArrayList<>();
// Fill the queue initially
processingQueue.addAll(tasks);
while (!processingQueue.isEmpty()) {
// Remove from the beginning (causes shifting of all elements)
Task task = processingQueue.remove(0);
processTask(task);
// Add new tasks at arbitrary positions
if (task.hasHighPriority()) {
// Insert at the beginning (causes shifting of all elements)
processingQueue.add(0, createFollowUpTask(task));
} else {
// Add somewhere in the middle based on priority
int insertPosition = findInsertPosition(processingQueue, task.getPriority());
processingQueue.add(insertPosition, createFollowUpTask(task));
}
}
}
// Better approach: Using LinkedList for frequent insertions/deletions
public void processTasksEfficiently(List<Task> tasks) {
LinkedList<Task> processingQueue = new LinkedList<>();
// Fill the queue initially
processingQueue.addAll(tasks);
while (!processingQueue.isEmpty()) {
// Remove from the beginning (O(1) operation for LinkedList)
Task task = processingQueue.removeFirst();
processTask(task);
// Add new tasks at appropriate positions
if (task.hasHighPriority()) {
// Insert at the beginning (O(1) operation for LinkedList)
processingQueue.addFirst(createFollowUpTask(task));
} else {
// For arbitrary insertions, LinkedList is still more efficient
// though still O(n) to find the position
int insertPosition = findInsertPosition(processingQueue, task.getPriority());
// Use a ListIterator to avoid traversing the list twice
ListIterator<Task> iterator = processingQueue.listIterator();
for (int i = 0; i < insertPosition; i++) {
iterator.next();
}
iterator.add(createFollowUpTask(task));
}
}
}
// Anti-pattern: Using array for frequent insertions/deletions
function processTasksInefficiently(tasks) {
const processingQueue = [...tasks];
while (processingQueue.length > 0) {
// Remove from the beginning (causes shifting of all elements)
const task = processingQueue.shift();
processTask(task);
// Add new tasks at arbitrary positions
if (task.hasHighPriority) {
// Insert at the beginning (causes shifting of all elements)
processingQueue.unshift(createFollowUpTask(task));
} else {
// Add somewhere in the middle based on priority
const insertPosition = findInsertPosition(processingQueue, task.priority);
processingQueue.splice(insertPosition, 0, createFollowUpTask(task));
}
}
}
// Better approach: Using a more appropriate data structure
function processTasksEfficiently(tasks) {
// For JavaScript, we can use a custom doubly-linked list implementation
// or a library that provides one
const processingQueue = new DoublyLinkedList();
// Fill the queue initially
for (const task of tasks) {
processingQueue.append(task);
}
while (!processingQueue.isEmpty()) {
// Remove from the beginning (O(1) operation)
const task = processingQueue.removeFirst();
processTask(task);
// Add new tasks at appropriate positions
if (task.hasHighPriority) {
processingQueue.prepend(createFollowUpTask(task));
} else {
// For a more efficient implementation, consider using a priority queue
// instead of finding insert positions manually
const newTask = createFollowUpTask(task);
processingQueue.insertAt(findInsertPosition(processingQueue, task.priority), newTask);
}
}
}
Using ArrayList (Java) or arrays (JavaScript) for frequent insertions or deletions, especially at the beginning or middle of the collection, leads to poor performance due to the need to shift elements.
To optimize insertions and deletions:
- Use LinkedList for frequent insertions/deletions at arbitrary positions
- Use ArrayDeque or Queue implementations for FIFO operations
- Consider using a priority queue for priority-based processing
- Use appropriate iterators to avoid traversing collections multiple times
- Be aware of the time complexity of operations for different collection types
- For JavaScript, consider using specialized data structure libraries
- Use custom implementations when built-in collections don’t meet requirements
- Consider the memory overhead of different collection types
// Anti-pattern: HashMap with poor hash function
public class BadKey {
private int id;
public BadKey(int id) {
this.id = id;
}
// Poor hash function that causes many collisions
@Override
public int hashCode() {
return id % 10; // Only uses last digit, causing many collisions
}
@Override
public boolean equals(Object obj) {
if (this == obj) return true;
if (obj == null || getClass() != obj.getClass()) return false;
BadKey other = (BadKey) obj;
return id == other.id;
}
}
// Usage that causes poor performance
Map<BadKey, String> map = new HashMap<>();
for (int i = 0; i < 10000; i++) {
map.put(new BadKey(i), "Value " + i);
}
// Better approach: Proper hash function
public class GoodKey {
private int id;
public GoodKey(int id) {
this.id = id;
}
// Better hash function with good distribution
@Override
public int hashCode() {
return Objects.hash(id); // Uses the entire id value
}
@Override
public boolean equals(Object obj) {
if (this == obj) return true;
if (obj == null || getClass() != obj.getClass()) return false;
GoodKey other = (GoodKey) obj;
return id == other.id;
}
}
// Anti-pattern: Using objects as keys without proper consideration
function processUserData(users) {
const userDataMap = {};
for (const user of users) {
// Using objects as keys without proper string conversion
// JavaScript will convert these to '[object Object]'
userDataMap[user] = calculateUserMetrics(user);
}
// This will likely not work as expected
return userDataMap[someUser];
}
// Better approach: Using proper keys or Map object
function processUserDataEfficiently(users) {
// Option 1: Using a unique identifier as key
const userDataMap = {};
for (const user of users) {
userDataMap[user.id] = calculateUserMetrics(user);
}
return userDataMap[someUser.id];
// Option 2: Using Map object which allows object keys
const userMap = new Map();
for (const user of users) {
userMap.set(user, calculateUserMetrics(user));
}
return userMap.get(someUser);
}
Using hash-based collections with poor hash functions leads to excessive hash collisions, degrading performance from O(1) to O(n) in worst cases.
To optimize hash-based collections:
- Implement proper hashCode() methods that use all relevant fields
- Ensure hash codes are well-distributed across the possible range
- Follow the contract: if two objects are equal, they must have the same hash code
- Use built-in hashing functions when available (Objects.hash in Java, etc.)
- Consider the load factor of hash-based collections
- Use appropriate initial capacity to minimize rehashing
- In JavaScript, prefer Map over object literals for complex keys
- Be cautious when using mutable objects as keys in hash-based collections
- Consider using specialized hash functions for specific use cases
// Anti-pattern: Inefficient collection iteration
public void processListInefficiently(List<String> items) {
// Repeatedly checking size in each iteration
for (int i = 0; i < items.size(); i++) {
// Using get() on a LinkedList is O(n)
String item = items.get(i);
processItem(item);
}
}
// Better approach: Efficient iteration
public void processListEfficiently(List<String> items) {
// For ArrayList: Cache the size
if (items instanceof ArrayList) {
int size = items.size();
for (int i = 0; i < size; i++) {
String item = items.get(i);
processItem(item);
}
}
// For LinkedList: Use iterator
else if (items instanceof LinkedList) {
for (String item : items) { // Uses Iterator internally
processItem(item);
}
}
// Generic approach that works well for both
else {
for (String item : items) {
processItem(item);
}
}
}
// Anti-pattern: Inefficient array iteration
function processArrayInefficiently(items) {
// Repeatedly checking length in each iteration
for (let i = 0; i < items.length; i++) {
processItem(items[i]);
}
}
// Better approach: Efficient iteration
function processArrayEfficiently(items) {
// Cache the length
const length = items.length;
for (let i = 0; i < length; i++) {
processItem(items[i]);
}
// Or use forEach (though slightly less performant in some cases)
items.forEach(item => processItem(item));
// Or use for...of loop (good for most cases)
for (const item of items) {
processItem(item);
}
}
Inefficient collection iteration, such as using inappropriate iteration methods for specific collection types or repeatedly accessing collection properties, can lead to significant performance degradation.
To optimize collection iteration:
- Use the appropriate iteration method for the collection type
- Cache collection size/length outside the loop
- Use enhanced for loops or iterators for linked collections
- Be aware of the time complexity of access operations
- Avoid modifying collections during iteration (use iterators with remove() when needed)
- Consider using specialized iteration methods (forEach, stream operations)
- Use indexed access only for random-access collections
- Be mindful of autoboxing/unboxing in loops
- Consider parallel iteration for large collections when appropriate
// Anti-pattern: Using HashMap when insertion order matters
public void processOrdersInefficiently(List<Order> orders) {
// HashMap doesn't maintain insertion order
Map<String, Order> orderMap = new HashMap<>();
for (Order order : orders) {
orderMap.put(order.getId(), order);
}
// Iterating over entries (order not preserved)
for (Map.Entry<String, Order> entry : orderMap.entrySet()) {
processOrderInSequence(entry.getValue());
}
}
// Better approach: Using the right Map implementation
public void processOrdersEfficiently(List<Order> orders) {
// LinkedHashMap maintains insertion order
Map<String, Order> orderMap = new LinkedHashMap<>();
for (Order order : orders) {
orderMap.put(order.getId(), order);
}
// Iterating over entries (insertion order preserved)
for (Map.Entry<String, Order> entry : orderMap.entrySet()) {
processOrderInSequence(entry.getValue());
}
}
// Another example: Using TreeMap for sorted keys
public void displayOrdersSorted(List<Order> orders) {
// TreeMap sorts entries by key
Map<LocalDateTime, Order> orderMap = new TreeMap<>();
for (Order order : orders) {
orderMap.put(order.getCreatedAt(), order);
}
// Iterating over entries (sorted by creation time)
for (Map.Entry<LocalDateTime, Order> entry : orderMap.entrySet()) {
displayOrder(entry.getValue());
}
}
// Anti-pattern: Using object when insertion order matters
function processOrdersInefficiently(orders) {
// Regular objects don't guarantee property insertion order
const orderMap = {};
for (const order of orders) {
orderMap[order.id] = order;
}
// Iterating over properties (order not guaranteed)
for (const orderId in orderMap) {
processOrderInSequence(orderMap[orderId]);
}
}
// Better approach: Using Map to preserve insertion order
function processOrdersEfficiently(orders) {
// Map preserves insertion order
const orderMap = new Map();
for (const order of orders) {
orderMap.set(order.id, order);
}
// Iterating over entries (insertion order preserved)
for (const [orderId, order] of orderMap.entries()) {
processOrderInSequence(order);
}
}
Using the wrong Map implementation for specific requirements, such as using HashMap when insertion order matters or using LinkedHashMap when sorted access is needed, leads to inefficient operations or additional sorting steps.
To choose the right Map implementation:
- Use HashMap for general-purpose key-value storage with no ordering requirements
- Use LinkedHashMap when insertion order matters
- Use TreeMap when sorted key order is required
- Use EnumMap for enum keys (Java)
- Consider ConcurrentHashMap for concurrent access
- In JavaScript, use Map for predictable iteration order
- Consider specialized map implementations for specific use cases
- Be aware of the performance characteristics of different map implementations
- Choose the implementation based on the most frequent operations
- Consider memory overhead when selecting an implementation
// Anti-pattern: Inefficient string concatenation
public String buildReportInefficiently(List<String> items) {
String report = "";
for (String item : items) {
// Creates a new String object in each iteration
report = report + item + "\n";
}
return report;
}
// Better approach: Using StringBuilder
public String buildReportEfficiently(List<String> items) {
// Preallocate capacity for better performance
StringBuilder reportBuilder = new StringBuilder(items.size() * 20); // Assuming average item length
for (String item : items) {
reportBuilder.append(item).append("\n");
}
return reportBuilder.toString();
}
// Anti-pattern: Inefficient string concatenation
function buildReportInefficiently(items) {
let report = '';
for (let i = 0; i < items.length; i++) {
// Creates a new string in each iteration
report = report + items[i] + '\n';
}
return report;
}
// Better approach: Using array join
function buildReportEfficiently(items) {
// Create array and join at the end (much more efficient)
return items.join('\n') + '\n';
// Alternative approach for more complex concatenation
const parts = [];
for (let i = 0; i < items.length; i++) {
parts.push(items[i]);
}
return parts.join('\n') + '\n';
}
Inefficient string concatenation, especially in loops, can lead to significant performance issues due to the immutable nature of strings, resulting in repeated memory allocations and copies.
To optimize string concatenation:
- Use StringBuilder or StringBuffer in Java
- Use array.join() in JavaScript
- Use ”.join(list) in Python
- Preallocate capacity when the final size is known or can be estimated
- Minimize the number of concatenation operations
- Consider using string interpolation or formatting for simple cases
- Use specialized libraries for very large string manipulations
- Be aware of the performance characteristics of string operations in your language
- Consider using string builders with chaining methods
// Anti-pattern: Excessive boxing and unboxing
public int sumValuesInefficiently(List<Integer> values) {
int sum = 0;
for (int i = 0; i < values.size(); i++) {
// Auto-unboxing Integer to int in each iteration
sum += values.get(i);
}
return sum;
}
// Better approach: Using primitive collections
public int sumValuesEfficiently(List<Integer> values) {
// Option 1: Minimize unboxing operations
int sum = 0;
for (Integer value : values) {
// Still unboxes, but at least avoids repeated get() calls
sum += value;
}
return sum;
// Option 2: Using streams with specialized sum operation
return values.stream().mapToInt(Integer::intValue).sum();
// Option 3: Using specialized primitive collections library
// (e.g., Trove, Fastutil, Eclipse Collections)
TIntList primitiveList = new TIntArrayList(values.size());
for (Integer value : values) {
primitiveList.add(value);
}
return primitiveList.sum();
}
// JavaScript doesn't have explicit boxing/unboxing,
// but there are similar performance concerns with type conversions
// Anti-pattern: Inefficient number parsing in a loop
function sumValuesInefficiently(values) {
let sum = 0;
for (let i = 0; i < values.length; i++) {
// Repeatedly parsing strings to numbers
sum += parseInt(values[i]);
}
return sum;
}
// Better approach: Convert once, then operate
function sumValuesEfficiently(values) {
// Convert all strings to numbers first
const numbers = values.map(value => parseInt(value));
// Then sum the numbers
let sum = 0;
for (let i = 0; i < numbers.length; i++) {
sum += numbers[i];
}
return sum;
// Or more concisely with reduce
return values.map(value => parseInt(value))
.reduce((sum, num) => sum + num, 0);
}
Excessive boxing and unboxing (converting between primitive types and their wrapper classes) can lead to significant performance overhead, especially in tight loops or when dealing with large collections.
To minimize boxing and unboxing:
- Use primitive arrays instead of collections when possible
- Consider specialized primitive collections libraries (Trove, Fastutil, Eclipse Collections in Java)
- Use specialized stream operations (mapToInt, mapToLong, etc.)
- Minimize conversions between primitive and wrapper types
- Be aware of autoboxing in arithmetic operations
- Cache boxed values when they need to be reused
- Use primitive-specialized methods when available
- Consider the memory overhead of wrapper objects
- In JavaScript, minimize type conversions in performance-critical code
- Batch conversions instead of performing them repeatedly
// Anti-pattern: Inefficient set operations
public List<String> findCommonElementsInefficiently(List<String> list1, List<String> list2) {
List<String> result = new ArrayList<>();
// O(n²) operation - checking each element against the other list
for (String item : list1) {
if (list2.contains(item)) { // Linear search in list2
result.add(item);
}
}
return result;
}
// Better approach: Using Set for efficient lookups
public List<String> findCommonElementsEfficiently(List<String> list1, List<String> list2) {
// Convert smaller list to Set for O(1) lookups
Set<String> set;
List<String> otherList;
if (list1.size() <= list2.size()) {
set = new HashSet<>(list1);
otherList = list2;
} else {
set = new HashSet<>(list2);
otherList = list1;
}
List<String> result = new ArrayList<>();
// Now check membership with O(1) lookups
for (String item : otherList) {
if (set.contains(item)) { // Constant-time operation
result.add(item);
}
}
return result;
// Even better: Using built-in set operations
Set<String> set1 = new HashSet<>(list1);
Set<String> set2 = new HashSet<>(list2);
set1.retainAll(set2); // Intersection operation
return new ArrayList<>(set1);
}
// Anti-pattern: Inefficient set operations
function findCommonElementsInefficiently(array1, array2) {
const result = [];
// O(n²) operation
for (const item of array1) {
if (array2.includes(item)) { // Linear search
result.push(item);
}
}
return result;
}
// Better approach: Using Set for efficient lookups
function findCommonElementsEfficiently(array1, array2) {
// Convert smaller array to Set for O(1) lookups
let set, otherArray;
if (array1.length <= array2.length) {
set = new Set(array1);
otherArray = array2;
} else {
set = new Set(array2);
otherArray = array1;
}
// Filter other array using the set
return otherArray.filter(item => set.has(item));
}
// Even better: Using Set intersection
function findCommonElementsWithSetIntersection(array1, array2) {
const set1 = new Set(array1);
const set2 = new Set(array2);
// Create intersection
return [...new Set([...set1].filter(item => set2.has(item)))];
}
Inefficient set operations, such as using lists or arrays for membership testing or set operations, can lead to quadratic time complexity instead of the linear or constant time that proper set implementations provide.
To optimize set operations:
- Use Set implementations for membership testing
- Convert collections to sets before performing set operations
- Use built-in set operations (retainAll, removeAll, etc.)
- Choose the appropriate set implementation for your needs
- Consider the trade-offs between HashSet, TreeSet, and LinkedHashSet
- Use specialized set operations libraries when available
- Be aware of the performance characteristics of different set operations
- Consider using BitSet for sets of integers within a bounded range
- In JavaScript, use Set objects for efficient lookups and set operations
- Consider the memory overhead of different set implementations
// Anti-pattern: Inefficient collection resizing
public List<String> buildLargeListInefficiently(int size) {
// Default initial capacity is 10
List<String> list = new ArrayList<>();
// Will cause multiple resizing operations
for (int i = 0; i < size; i++) {
list.add("Item " + i);
}
return list;
}
// Better approach: Preallocating capacity
public List<String> buildLargeListEfficiently(int size) {
// Preallocate with known capacity
List<String> list = new ArrayList<>(size);
// No resizing needed
for (int i = 0; i < size; i++) {
list.add("Item " + i);
}
return list;
}
// Anti-pattern: Inefficient array growth
function buildLargeArrayInefficiently(size) {
const array = [];
// Will cause multiple internal resizing operations
for (let i = 0; i < size; i++) {
array.push(`Item ${i}`);
}
return array;
}
// Better approach: Preallocating array
function buildLargeArrayEfficiently(size) {
// Preallocate array with known size
const array = new Array(size);
// Fill array without resizing
for (let i = 0; i < size; i++) {
array[i] = `Item ${i}`;
}
return array;
}
Inefficient collection resizing, such as not preallocating capacity for collections that will grow to a known or estimated size, leads to multiple expensive resize operations that involve copying elements to new, larger backing arrays.
To optimize collection sizing:
- Preallocate collections with appropriate initial capacity when size is known
- Estimate capacity when exact size is unknown
- Be aware of the default capacities and growth factors of collections
- Consider the memory-time trade-off of preallocating capacity
- Use specialized collections with custom growth strategies when needed
- Avoid excessive preallocations that waste memory
- Consider using array-based collections for better memory locality
- In JavaScript, preallocate arrays when size is known
- Be mindful of the memory overhead of empty preallocated slots
- Consider trimming oversized collections after bulk operations
// Anti-pattern: Inefficient multi-dimensional array access
public void processMatrixInefficiently(int[][] matrix) {
int rows = matrix.length;
int cols = matrix[0].length;
// Column-major traversal in a row-major array
for (int col = 0; col < cols; col++) {
for (int row = 0; row < rows; row++) {
// Poor cache locality
processElement(matrix[row][col]);
}
}
}
// Better approach: Cache-friendly traversal
public void processMatrixEfficiently(int[][] matrix) {
int rows = matrix.length;
int cols = matrix[0].length;
// Row-major traversal in a row-major array
for (int row = 0; row < rows; row++) {
for (int col = 0; col < cols; col++) {
// Better cache locality
processElement(matrix[row][col]);
}
}
}
// Anti-pattern: Inefficient multi-dimensional array access
function processMatrixInefficiently(matrix) {
const rows = matrix.length;
const cols = matrix[0].length;
// Column-major traversal in a row-major array
for (let col = 0; col < cols; col++) {
for (let row = 0; row < rows; row++) {
// Poor cache locality
processElement(matrix[row][col]);
}
}
}
// Better approach: Cache-friendly traversal
function processMatrixEfficiently(matrix) {
const rows = matrix.length;
const cols = matrix[0].length;
// Row-major traversal in a row-major array
for (let row = 0; row < rows; row++) {
for (let col = 0; col < cols; col++) {
// Better cache locality
processElement(matrix[row][col]);
}
}
}
Inefficient multi-dimensional array access patterns, particularly traversing arrays in a way that doesn’t match their memory layout, can lead to poor cache locality and significantly reduced performance.
To optimize multi-dimensional array operations:
- Match traversal order to the array’s memory layout (row-major vs. column-major)
- Consider using flattened 1D arrays for better cache performance
- Use appropriate indexing calculations for flattened arrays
- Be aware of the memory layout in your programming language
- Consider using specialized matrix libraries for large-scale operations
- Implement blocking/tiling for large matrices to improve cache utilization
- Minimize array dimension lookups in inner loops
- Consider using array views or slices for subarray operations
- Be mindful of padding and alignment in multi-dimensional arrays
- Use appropriate data structures for sparse matrices
Data Structure Selection Checklist:
1. Access Pattern Analysis
- Identify the most frequent operations (add, remove, search, iterate)
- Determine if random access or sequential access is needed
- Consider if ordering is important (insertion order, natural order)
- Evaluate the frequency of modifications vs. reads
- Determine if duplicate elements are allowed
2. Collection Type Selection
- Lists: ArrayList for random access, LinkedList for frequent insertions/deletions
- Sets: HashSet for fast lookups, TreeSet for ordered elements, LinkedHashSet for insertion order
- Maps: HashMap for fast lookups, TreeMap for sorted keys, LinkedHashMap for insertion order
- Queues: ArrayDeque for FIFO, PriorityQueue for priority-based processing
- Specialized: Consider BitSet, EnumSet, EnumMap for specific use cases
3. Performance Considerations
- Estimate the expected size of the collection
- Consider memory constraints and overhead
- Evaluate the impact of resizing operations
- Consider thread-safety requirements
- Evaluate the need for primitive collections vs. object collections
4. Implementation Details
- Preallocate collections with known or estimated size
- Implement proper equals() and hashCode() for custom keys
- Consider immutability for keys in hash-based collections
- Use appropriate iteration methods for the collection type
- Implement proper cleanup for large temporary collections
5. Special Cases
- Very large collections: Consider specialized libraries or external storage
- Concurrent access: Use thread-safe collections or proper synchronization
- Memory-constrained environments: Consider compact representations
- Performance-critical code: Consider custom implementations or specialized libraries
- Specific algorithms: Match data structures to algorithmic requirements
Selecting the appropriate data structure for a specific use case is crucial for application performance and resource utilization. The wrong data structure can lead to inefficient operations, excessive memory usage, and poor scalability.
Key selection criteria:
- Operation complexity: Choose data structures with efficient operations for your most frequent use cases
- Memory usage: Consider the memory overhead of different data structures
- Access patterns: Match the data structure to your access patterns (sequential, random, ordered)
- Mutability requirements: Consider immutable collections for thread safety
- Specialized needs: Use specialized collections for specific use cases
- Implementation details: Consider the underlying implementation of collections
- Language-specific considerations: Be aware of the performance characteristics in your language
- Scaling requirements: Consider how the data structure will perform as data grows
- Concurrency needs: Choose thread-safe collections when needed
- Benchmark with realistic data: Test performance with representative data volumes and patterns