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BitLogger/docs/api/runtime-sink-file-set-auto-flush.md
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---
name: runtime-sink-file-set-auto-flush
group: api
category: runtime
update-time: 20260613
description: Update the auto-flush policy used by a file-backed RuntimeSink.
key-word:
- runtime
- sink
- file
- public
---
## Runtime-sink-file-set-auto-flush
Update the auto-flush policy used by a file-backed `RuntimeSink`. This helper changes direct runtime durability behavior without rebuilding or rewrapping the sink.
### Interface
```moonbit
pub fn RuntimeSink::file_set_auto_flush(self : RuntimeSink, enabled : Bool) -> Bool {
```
#### input
- `self : RuntimeSink` - Runtime sink whose file auto-flush policy should change.
- `enabled : Bool` - New auto-flush setting.
#### output
- `Bool` - Whether the policy update was applied.
### Explanation
Detailed rules explaining key parameters and behaviors
- Plain `File` runtime variants update the wrapped `FileSink` auto-flush policy and return `true`.
- `QueuedFile` runtime variants forward the update to the wrapped inner `FileSink` and return `true`.
- Non-file runtime variants return `false`.
- This helper changes policy only; it does not itself flush pending data.
### How to Use
Here are some specific examples provided.
#### When Need Direct Runtime Durability Tuning
When a file-backed runtime sink should start flushing each write automatically:
```moonbit
ignore(sink.file_set_auto_flush(true))
```
In this example, runtime durability policy is updated without rebuilding the sink.
#### When Need To Relax Flush Pressure On A Runtime Sink
When file writes should stop auto-flushing for throughput reasons:
```moonbit
let ok = sink.file_set_auto_flush(false)
```
In this example, the call site updates policy explicitly and can inspect the result.
### Error Case
e.g.:
- If the runtime sink is not file-backed, the method returns `false`.
- If callers need an immediate flush action, `file_flush()` is the operational API.
### Notes
1. Use this helper for direct runtime durability tuning on `RuntimeSink` values.
2. Pair it with `file_auto_flush()` to verify the active policy.