Backend Language Proficiency Questions

// assumes DataSource ds, List<Record> records
String sql = "INSERT INTO items(id, val, updated_at) VALUES (?, ?, ?)" +
             " ON CONFLICT (id) DO UPDATE SET val = EXCLUDED.val, updated_at = EXCLUDED.updated_at";
int CHUNK = 1000;

try (Connection conn = ds.getConnection();
     PreparedStatement ps = conn.prepareStatement(sql)) {
    conn.setAutoCommit(false);
    int count = 0;
    for (Record r : records) {
        ps.setInt(1, r.id);
        ps.setString(2, r.val);
        ps.setTimestamp(3, new Timestamp(r.updatedAt));
        ps.addBatch();
        if (++count % CHUNK == 0) {
            try {
                ps.executeBatch();
                conn.commit();              // commit chunk
                // persist checkpoint (e.g., last processed index/id)
            } catch (SQLException e) {
                conn.rollback();
                // handle partial failure: retry batch, log failed rows, escalate
                throw e;
            }
        }
    }
    if (count % CHUNK != 0) {
        ps.executeBatch();
        conn.commit();
        // persist final checkpoint
    }
}

# pseudocode / Python-like
import random, time

def backoff_delay(attempt, base=0.1, max_delay=10.0, cap_retries=5, jitter='full', prev_delay=None):
    """
    attempt: 0-based attempt number
    base: base delay seconds
    max_delay: max single delay seconds
    cap_retries: maximum attempts (caller should enforce)
    jitter: 'none'|'full'|'equal'|'decorrelated'
    prev_delay: previous delay for decorrelated jitter
    returns (delay_seconds, next_prev_delay)
    """
    expo = base * (2 ** attempt)
    unjittered = min(expo, max_delay)

    if jitter == 'none':
        delay = unjittered

    elif jitter == 'full':
        # uniform between 0 and unjittered
        delay = random.uniform(0, unjittered)

    elif jitter == 'equal':
        # half of unjittered plus uniform half
        half = unjittered / 2.0
        delay = half + random.uniform(0, half)

    elif jitter == 'decorrelated':
        # from "Exponential Backoff And Jitter" blog
        # new = min(max(base, random(prev_delay * 3, unjittered)), max_delay)
        if prev_delay is None:
            prev = base
        else:
            prev = prev_delay
        # choose random between base and prev*3, then clamp
        candidate = random.uniform(base, prev * 3)
        delay = min(candidate, max_delay)
    else:
        raise ValueError("unknown jitter")

    return delay, delay  # return delay and store as prev_delay for decorrelated

import time, requests, jwt
from jwt import algorithms

JWKS_URL = "https://idp.example/.well-known/jwks.json"
AUD = "my-audience"
ISS = "https://idp.example/"

def get_public_key(kid):
    jwks = requests.get(JWKS_URL).json()
    for k in jwks["keys"]:
        if k["kid"] == kid:
            return algorithms.RSAAlgorithm.from_jwk(json.dumps(k))
    raise Exception("Key not found")

def validate(token):
    header = jwt.get_unverified_header(token)
    key = get_public_key(header["kid"])
    # allow 60s clock skew
    return jwt.decode(token, key=key, algorithms=["RS256"], audience=AUD, issuer=ISS, leeway=60)

// Use com.nimbusds:nimbus-jose-jwt
SignedJWT jwt = SignedJWT.parse(token);
JWSHeader header = jwt.getHeader();
JWK jwk = jwkSet.getKeyByKeyId(header.getKeyID());
// verify signature with RSA public key
RSAKey rsa = (RSAKey) jwk;
if (!jwt.verify(new RSASSAVerifier(rsa.toRSAPublicKey()))) throw ...
// claims validation with allowed clock skew
JWTClaimsSet claims = jwt.getJWTClaimsSet();
Date now = new Date();
if (claims.getExpirationTime().before(new Date(now.getTime() - 60000))) throw ...
// check nbf, iat, iss, aud similarly