[GitHub] [hudi] loukey-lj commented on a diff in pull request #6612: [RFC-58][HUDI-4790] a more effective HoodieMergeHandler for COW table with parquet

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loukey-lj commented on code in PR #6612:
URL: https://github.com/apache/hudi/pull/6612#discussion_r1060261800


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rfc/rfc-58/rfc-58.md:
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+
+# RFC-58: A more effective HoodieMergeHandler for COW table with parquet
+
+## Proposers
+
+*   @loukey-lj
+
+## Approvers
+
+*   @<approver1 github username>
+
+*   @<approver2 github username>
+
+## Status
+
+JIRA: https://issues.apache.org/jira/browse/HUDI-4790
+
+> Please keep the status updated in `rfc/README.md`.
+
+## Abstract
+
+To provide a more effective HoodieMergeHandler for COW table with parquet. Hudi rewrite whole parquet file every COW, that costs a lot in De/serialization and De/compression.  To decrease this cost, a 'surgery' is introduced, which rebuilds a new parquet from an old one,  just copying unchanged rowGroups and overwriting changed rowGroups when updating parquet files.
+
+## Background
+
+*   Parquet is a columnar storage format. All data is horizontally divided into row groups. A row group contains the column chunks of all columns in the interval corresponding to this row group. A column chunk is composed of pages, which are compression and coding units. 
+
+*   In current version of Hudi, a complex De/serialization and De/compression happens every time upserting long tail data on COW, which causes giant CPU/IO cost.
+
+*   The purpose of current RFC aims to decrease costs of De/serialization and De/compression in upserting.  Try to think about the reality, if we know which row groups need to be updated and even more the columns need to be updated in these row groups, we can skip much data's de/serialization and de/compression. That brings giant improvement.

Review Comment:
   It has nothing to do with what payload is used. It is important to know which columns need to be updated and which columns do not need to be updated. If we know which columns need to be updated, even if OverwriteWithLatestAvroPayload is used, it can be partially updated. The copy of rowGroup is applicable to all Payloads. My current scenario is based on merge into. The updated columns come from the syntax parsing of SQL, and then are set in conf



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