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administration: backpressure: paused -> resume (#1216) #1229

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Oct 10, 2023
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administration: backpressure: paused -> resume (#1216) #1229

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2 changes: 1 addition & 1 deletion administration/backpressure.md
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Expand Up @@ -6,7 +6,7 @@ In order to avoid backpressure, Fluent Bit implements a mechanism in the engine

As described in the [Buffering](../concepts/buffering.md) concepts section, Fluent Bit offers two modes for data handling: in-memory only (default) and in-memory + filesystem \(optional\).

The default `storage.type memory` buffer can be restricted with **Mem\_Buf\_Limit**. If memory reaches this limit and you reach a backpressure scenario, you will not be able to ingest more data until the data chunks that are in memory can be flushed. The input will be paused and Fluent Bit will [emit](https://github.com/fluent/fluent-bit/blob/v2.0.0/src/flb_input_chunk.c#L1334) a `[warn] [input] {input name or alias} paused (mem buf overlimit)` log message. Depending on the input plugin in use, this might lead to discard incoming data \(e.g: TCP input plugin\). The tail plugin can handle pause without data loss; it will store its current file offset and resume reading later. When buffer memory is available, the input will resume collecting/accepting logs and Fluent Bit will [emit](https://github.com/fluent/fluent-bit/blob/v2.0.0/src/flb_input_chunk.c#L1277) a `[info] [input] {input name or alias} paused (mem buf overlimit)` message.
The default `storage.type memory` buffer can be restricted with **Mem\_Buf\_Limit**. If memory reaches this limit and you reach a backpressure scenario, you will not be able to ingest more data until the data chunks that are in memory can be flushed. The input will be paused and Fluent Bit will [emit](https://github.com/fluent/fluent-bit/blob/v2.0.0/src/flb_input_chunk.c#L1334) a `[warn] [input] {input name or alias} paused (mem buf overlimit)` log message. Depending on the input plugin in use, this might lead to discard incoming data \(e.g: TCP input plugin\). The tail plugin can handle pause without data loss; it will store its current file offset and resume reading later. When buffer memory is available, the input will resume collecting/accepting logs and Fluent Bit will [emit](https://github.com/fluent/fluent-bit/blob/v2.0.0/src/flb_input_chunk.c#L1277) a `[info] [input] {input name or alias} resume (mem buf overlimit)` message.

This risk of data loss can be mitigated by configuring secondary storage on the filesystem using the `storage.type` of `filesystem` \(as described in [Buffering & Storage](buffering-and-storage.md)\). Initially, logs will be buffered to *both* memory and filesystem. When the `storage.max_chunks_up` limit is reached, all the new data will be stored safely only in the filesystem. Fluent Bit will stop enqueueing new data in memory and will only buffer to the filesystem. Please note that when `storage.type filesystem` is set, the `Mem_Buf_Limit` setting no longer has any effect, instead, the `[SERVICE]` level `storage.max_chunks_up` setting controls the size of the memory buffer.

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