Limits

Configurable runtime limits

These defaults come from the runtime’s src/config.js. Set overrides in the vars section of atoms-worker/wrangler.jsonc.

Setting	Default	Applies to
ATOMS_MAX_REQUEST_BYTES	1,048,576 bytes (1 MiB)	One invocation body
ATOMS_MAX_ATOM_ID_BYTES	256 bytes	One Atom id
ATOMS_MAX_JSON_DEPTH	64 levels	Invocation arguments
ATOMS_SQL_MAX_ROWS	100,000 rows	One SQL result
ATOMS_SQL_MAX_RESULT_BYTES	8,388,608 bytes (8 MiB)	One SQL result
ATOMS_SQL_MAX_BINDINGS	1,000 values	One SQL statement
ATOMS_TURN_DEADLINE_MS	30,000 ms	Total time awaiting callbacks in one turn
ATOMS_CALLBACK_TIMEOUT_MS	10,000 ms	One callback request
ATOMS_CALLBACK_MAX_REQUEST_BYTES	1,048,576 bytes (1 MiB)	One callback request body
ATOMS_CALLBACK_MAX_RESPONSE_BYTES	1,048,576 bytes (1 MiB)	One synchronous callback response
ATOMS_MAX_DISPATCHES_PER_TURN	100 jobs	One turn
ATOMS_WS_MAX_CHANNELS	8 channels	One WebSocket connection
ATOMS_WS_MAX_MESSAGE_BYTES	131,072 bytes (128 KiB)	One incoming WebSocket message
ATOMS_WS_MAX_SEND_BYTES	131,072 bytes (128 KiB)	One outgoing message or broadcast frame
ATOMS_WS_MAX_BROADCAST_SOCKETS	1,000 sockets	One broadcast
ATOMS_TIMERS_MAX	10,000 timers	One Atom
ATOMS_TIMER_NAME_MAX_BYTES	256 bytes	One timer name
ATOMS_TIMERS_MAX_PER_ALARM	100 timers	One alarm event; remaining work is rescheduled

Cloudflare also enforces platform limits, including CPU and memory. Check the Durable Objects limits for your deployment.

The clock does not advance inside a turn

On the deployed runtime, the PHP clock does not advance during CPU work or synchronous SQL. sleep(), usleep(), and elapsed-time loops can block until Cloudflare resets the Atom for exceeding its CPU limit.

Install the PHPStan rules:

composer require --dev atoms/phpstan-rules:^0.6

includes:
    - vendor/atoms/phpstan-rules/rules.neon

The rules report ATOMS-E101 for sleep-family calls in Atom code and ATOMS-E102 for elapsed-time wait loops. They check each method individually and may miss waits reached through other method calls.

Use a named timer to act in a later turn, or dispatch() to hand work to the application.

Read large integers as text

Cloudflare’s SQLite API exposes numeric results to JavaScript as numbers. An INTEGER above 2^53-1 may already be rounded before the Atoms bridge sees it, so the default runtime rejects the result with an int64_precision error.

Store signed 64-bit integers normally, but select them as text when reading:

SELECT CAST(large_integer AS TEXT) AS large_integer FROM counters;

The runtime preserves signed 64-bit integer values when writing them. The precision limit applies when reading numeric results through JavaScript; it also affects negative integers below -(2^53-1).

PDO is a compatibility shim

$this->db()->pdo() looks like PDO but executes against Durable Object SQLite across the PHP↔JavaScript bridge. Unsupported operations and fetch modes throw PDOException. Review PDO compatibility before porting code that relies on driver attributes, extension callbacks, duplicate column names, or uncommon fetch modes.

Payloads and results are bounded

Invocation bodies, callback bodies, callback results, SQL row counts, SQL result bytes, nesting depth, and binding counts are bounded through Worker configuration. Exceeding a boundary returns a stable error. Page large query results and send only the data a callback needs.

Binary values crossing JSON are tagged and base64 encoded. WebSocket binary frames remain binary on the socket side, but callback and invocation envelopes are JSON.

Delivery semantics

• dispatch() is at-most-once, unordered, and unretried. A transport failure is logged and dropped.
• A timer is one-shot and at-most-once; handler failure is not retried automatically.
• WebSocket sends are not part of a SQL transaction and remain visible after rollback.
• app() cannot run inside a database transaction.
• Deployments and secret changes take time to reach running Atoms.

Memory and persistence

PHP and the Worker share the available runtime memory. Process large results in pages and store persistent state in SQLite. PHP properties are lost when Cloudflare evicts an idle Atom; its database, hibernating WebSocket connections, and scheduled timers survive.

Data recovery and billing

See Rollback for data recovery limitations. Atoms 0.6 requires the Workers Paid plan. See Durable Objects pricing for billing details.