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2) any schema change will directly applied to this first id-schema and saved with commit file

let's give a exmaple:

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now rename operationTime to col1:

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read operation:

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1. when we read the old file, the first id-schema will be used as file-schema. lastest id-schema will be used as qurey-schema. then we use merge module to merge file-schema and query-schema to produce the final read-schema. once read-schema is produced, we can read the old files correctly.how to merge file-schema and query-schema pls see the chapter Data query process

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   2. when we read the new file, the lastest id-schema will be used as file-schema and qurey-schema the remaining process are same as (1)

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write operation:

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