BigData / Apache Hudi Interview Questions
What is Merge-on-Read (MoR) in Hudi?
In a Merge-on-Read table, updates aren't merged into the base Parquet file right away. Instead they're appended to small row-based Avro log files attached to that file group, and the merge is deferred until read time or until a background compaction runs.
This makes writes much cheaper — appending to a log file is far faster than rewriting a whole Parquet file — at the cost of read queries needing to merge base and log data on the fly (unless a read-optimized query is used, which skips unmerged logs for speed at the expense of freshness). MoR is the natural fit for write-heavy, high-frequency CDC ingestion.
In a MoR table, updates are first written to:
MoR trades cheaper writes for:
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