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• Currently, when set 'changelog-producer' = 'lookup', the data write behavior is not atomic but divided into two steps: first, data is written to create snapshot1, then lookup compaction generates snapshot2. We need to consider the atomicity of this.
• In most cases, the data will be transferred to level-0 first, and then rewritten. The writing overhead is a bit high, and perhaps some optimization can be done in this regard.
• If change log needs to be generated, in theory, change log and delete file can be produced simultaneously (without reading twice).
• The merge engine is still available.

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1. Impact on file meta: Currently, the stats (min, max, null count) in file meta are already unreliable, so no special handling will be performed for this aspect.
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Compatibility, Deprecation, and Migration Plan

Conversion between delete file mode (just temporarily call it) and original LSM

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