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Nanaloveyuki
71 lines
2.2 KiB
Markdown
71 lines
2.2 KiB
Markdown
---
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name: queue-overflow-policy
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group: api
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category: sink
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update-time: 20260613
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description: Public overflow policy alias used by synchronous queued sinks and queue config.
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key-word:
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- queue
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- overflow
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- alias
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- public
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---
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## Queue-overflow-policy
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`QueueOverflowPolicy` is the public enum that defines what a synchronous queue should do when it reaches `max_pending`. It is a direct alias to the queue model enum used by both `QueuedSink` and `QueueConfig`.
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### Interface
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```moonbit
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pub type QueueOverflowPolicy = @utils.QueueOverflowPolicy
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```
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#### output
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- `QueueOverflowPolicy` - Public synchronous queue overflow enum with the variants `DropNewest` and `DropOldest`.
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### Explanation
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Detailed rules explaining key parameters and behaviors
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- This is a type alias, not a separate policy wrapper.
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- `QueueOverflowPolicy::DropNewest` keeps the existing queued records and drops the incoming one when the queue is full.
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- `QueueOverflowPolicy::DropOldest` removes one pending record and enqueues the new record instead.
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- The same enum is used by code-side queue composition through `queued_sink(...)` and config-driven queue composition through `QueueConfig::new(...)`.
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### How to Use
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Here are some specific examples provided.
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#### When Need A Bounded Queue That Prefers Older Pending Records
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When the oldest pending records should be preserved and new bursts can be dropped:
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```moonbit
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let sink = queued_sink(console_sink(), max_pending=32, overflow=QueueOverflowPolicy::DropNewest)
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```
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In this example, new records are discarded once the queue is full.
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#### When Need To Prefer Fresh Records Over Old Pending Work
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When backlog should make room for newer records:
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```moonbit
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let queue = QueueConfig::new(32, overflow=QueueOverflowPolicy::DropOldest)
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```
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In this example, the oldest pending record is removed when the queue overflows.
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### Error Case
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e.g.:
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- If a queue is unbounded or never reaches capacity, the overflow policy has no effect.
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- If parsed JSON uses unsupported overflow text, config parsing raises `ConfigError`.
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### Notes
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1. This policy belongs to synchronous queue wrappers, not `bitlogger_async`.
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2. Use `AsyncOverflowPolicy` for the async logger queue behavior.
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