[Bug]Chunking Setting in file web, The previously added chunk data will be lost.

[Mzs-code]

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Dify version

1.7.1

Cloud or Self Hosted

Cloud, Self Hosted (Docker)

Steps to reproduce

This is a very dangerous bug.😭
We lost all the test data :(

1. upload file in knowledge

2. add chunk use Web or API

3. Save Chunking Setting(Whether modified or not)

4. Previously added chunk will lost

2025-08-01.16.15.08.mov

✔️ Expected Behavior

Previously added chunk no lost.

❌ Actual Behavior

No response

[dosubot]

This data loss happens because saving the chunking settings in the web UI triggers backend logic that can wipe and rebuild all chunk data—even if you didn't actually change any settings. The backend treats every save as a potential change and may launch a reindexing task that deletes and recreates chunks and their vector indexes, which leads to the loss of previously added chunk data if safeguards aren't in place to detect no-op saves or preserve custom chunks. There's currently no explicit protection against this in the workflow, which is why you're seeing this dangerous behavior in 1.7.1 [code reference].

Until this is fixed, avoid saving chunking settings unless absolutely necessary, and always back up your data before making changes. There are no documented workarounds or fixes for this specific issue yet. If you need to recover lost data, you would have to restore from a backup.

To reply, just mention @dosu.

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[JohnJyong]

the action re-chunk will splite your original file and cover your current documen .

[Mzs-code]

@JohnJyong I understand your explanation.
But, It is no described anywhere, 'change Chunking Setting will base original file '

Intuitively from the use of products, When the function of add chunk(web or api) is provided,
the action re-chunk base latest data will be better.

On the other hand, updating the knowledge base step by step is more realistic.

[Mzs-code]

Because the built-in Delimiter function is not satisfied, we uploaded 1000 chunks using api.

[Mzs-code]

I suggest that a strong prompt should be added to the save&process button.
This is the simplest way at present.