Limits

Cloudflare plan and platform limits

Atoms 0.6 requires the Workers Paid plan. See Durable Objects pricing for billing.

Cloudflare also enforces its own limits, including CPU time and memory. See Durable Objects limits.

Configurable runtime limits

Override any of these 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

An invocation, callback, or SQL result over its limit fails with an error instead of being truncated. Page large query results, and send a callback only the data it needs.

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 on its own, so they can miss a wait reached through another method call.

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

Read large integers as text

Cloudflare’s SQLite API returns numbers to the runtime as JavaScript numbers, so an INTEGER above 2^53-1 (or below -(2^53-1)) can be rounded before Atoms sees it. Rather than return a wrong value, the runtime fails the query with an int64_precision error.

Writing signed 64-bit integers is exact. When reading them, select them as text:

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

Binary data

Arguments, return values, SQL values, and callback payloads travel as JSON, so they must be valid UTF-8. Base64-encode binary data yourself and store it as text; SQLite BLOB values and PDO::PARAM_LOB are not supported. WebSocket messages are the exception: send() delivers bytes that are not valid UTF-8 as a binary frame.