87 lines
2.9 KiB
Java
87 lines
2.9 KiB
Java
package implementations.java.consistent_hashing;
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import java.security.MessageDigest;
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import java.security.NoSuchAlgorithmException;
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import java.util.*;
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public class ConsistentHashing {
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private final int numReplicas; // Number of virtual nodes per server
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private final TreeMap<Long, String> ring; // Hash ring storing virtual nodes
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private final Set<String> servers; // Set of physical servers
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public ConsistentHashing(List<String> servers, int numReplicas) {
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this.numReplicas = numReplicas;
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this.ring = new TreeMap<>();
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this.servers = new HashSet<>();
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// Add each server to the hash ring
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for (String server : servers) {
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addServer(server);
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}
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}
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private long hash(String key) {
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try {
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MessageDigest md = MessageDigest.getInstance("MD5");
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md.update(key.getBytes());
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byte[] digest = md.digest();
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return ((long) (digest[0] & 0xFF) << 24) |
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((long) (digest[1] & 0xFF) << 16) |
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((long) (digest[2] & 0xFF) << 8) |
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((long) (digest[3] & 0xFF));
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} catch (NoSuchAlgorithmException e) {
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throw new RuntimeException("MD5 algorithm not found", e);
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}
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}
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public void addServer(String server) {
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servers.add(server);
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for (int i = 0; i < numReplicas; i++) {
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long hash = hash(server + "-" + i); // Unique hash for each virtual node
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ring.put(hash, server);
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}
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}
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public void removeServer(String server) {
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if (servers.remove(server)) {
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for (int i = 0; i < numReplicas; i++) {
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long hash = hash(server + "-" + i);
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ring.remove(hash);
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}
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}
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}
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public String getServer(String key) {
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if (ring.isEmpty()) {
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return null; // No servers available
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}
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long hash = hash(key);
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// Find the closest server in a clockwise direction
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Map.Entry<Long, String> entry = ring.ceilingEntry(hash);
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if (entry == null) {
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// If we exceed the highest node, wrap around to the first node
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entry = ring.firstEntry();
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}
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return entry.getValue();
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}
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public static void main(String[] args) {
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List<String> servers = Arrays.asList("S0", "S1", "S2", "S3", "S4", "S5");
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ConsistentHashing ch = new ConsistentHashing(servers, 3);
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// Step 2: Assign requests (keys) to servers
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System.out.println("UserA is assigned to: " + ch.getServer("UserA"));
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System.out.println("UserB is assigned to: " + ch.getServer("UserB"));
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// Step 3: Add a new server dynamically
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ch.addServer("S6");
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System.out.println("UserA is now assigned to: " + ch.getServer("UserA"));
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// Step 4: Remove a server dynamically
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ch.removeServer("S2");
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System.out.println("UserB is now assigned to: " + ch.getServer("UserB"));
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}
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}
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