KV Gotchas & Troubleshooting

Common Errors

"Stale Read After Write"

Cause: Eventual consistency means writes may not be immediately visible in other regions
Solution: Don't read immediately after write; return confirmation without reading or use the local value you just wrote. Writes visible immediately in same location, ≤60s globally

// ❌ BAD: Read immediately after write
await env.KV.put("key", "value");
const value = await env.KV.get("key"); // May be null in other regions!

// ✅ GOOD: Use the value you just wrote
const newValue = "value";
await env.KV.put("key", newValue);
return new Response(newValue); // Don't re-read

"429 Rate Limit on Concurrent Writes"

Cause: Multiple concurrent writes to same key exceeding 1 write/second limit
Solution: Use sequential writes, unique keys for concurrent operations, or implement retry with exponential backoff

async function putWithRetry(
  kv: KVNamespace,
  key: string,
  value: string,
  maxAttempts = 5
): Promise<void> {
  let delay = 1000;
  for (let i = 0; i < maxAttempts; i++) {
    try {
      await kv.put(key, value);
      return;
    } catch (err) {
      if (err instanceof Error && err.message.includes("429")) {
        if (i === maxAttempts - 1) throw err;
        await new Promise(r => setTimeout(r, delay));
        delay *= 2; // Exponential backoff
      } else {
        throw err;
      }
    }
  }
}

"Inefficient Multiple Gets"

Cause: Making multiple individual get() calls instead of bulk operation
Solution: Use bulk get with array of keys: env.USERS.get(["user:1", "user:2", "user:3"]) to reduce to 1 operation

"Null Reference Error"

Cause: Attempting to use value without checking for null when key doesn't exist
Solution: Always handle null returns - KV returns null for missing keys, not undefined

// ❌ BAD: Assumes value exists
const config = await env.KV.get("config", "json");
return config.theme; // TypeError if null!

// ✅ GOOD: Null checks
const config = await env.KV.get("config", "json");
return config?.theme ?? "default";

// ✅ GOOD: Early return
const config = await env.KV.get("config", "json");
if (!config) return new Response("Not found", { status: 404 });
return new Response(config.theme);

"Negative Lookup Caching"

Cause: Keys that don't exist are cached as "not found" for up to 60s
Solution: Creating a key after checking won't be visible until cache expires

// Check → create pattern has race condition
const exists = await env.KV.get("key"); // null, cached as "not found"
if (!exists) {
  await env.KV.put("key", "value");
  // Next get() may still return null for ~60s due to negative cache
}

// Alternative: Always assume key may not exist, use defaults
const value = await env.KV.get("key") ?? "default-value";

Performance Tips

Cost Examples

Free tier:

• 100K reads/day = 3M/month ✅
• 1K writes/day = 30K/month ✅
• 1GB storage ✅

Example paid workload:

• 10M reads/month = $5.00
• 100K writes/month = $0.50
• 1GB storage = $0.50
• Total: ~$6/month

Limits