[GitHub] [hudi] Gatsby-Lee commented on a diff in pull request #3549: [HUDI-2369] Blog on bulk_insert sort modes

["Gatsby-Lee (via GitHub)" <gi...@apache.org>]

Gatsby-Lee commented on code in PR #3549:
URL: https://github.com/apache/hudi/pull/3549#discussion_r1096835196


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website/blog/2021-08-27-bulk-insert-sort-modes.md:
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+---
+title: "Bulk Insert Sort Modes with Apache Hudi"
+excerpt: "Different sort modes available with BulkInsert"
+author: shivnarayan
+category: blog
+---
+
+Apache Hudi supports a `bulk_insert` operation in addition to "insert" and "upsert" to ingest data into a hudi table. 
+There are different sort modes that one could employ while using bulk_insert. This blog will talk about 
+different sort modes available out of the box, and how each compares with others. 
+<!--truncate-->
+
+Apache Hudi supports “bulk_insert” to assist in initial loading of data to a hudi table. This is expected
+to be faster when compared to using “insert” or “upsert” operations. Bulk insert differs from insert in two
+aspects. Existing records are never looked up with bulk_insert, and some writer side optimizations like 
+small files are not managed with bulk_insert. 
+
+Bulk insert offers 3 different sort modes to cater to different needs of users, based on the following principles.
+
+- Sorting will give us good compression and upsert performance, if data is laid out well. Especially if your record keys 
+  have some sort of ordering (timestamp, etc) characteristics, sorting will assist in trimming down a lot of files 
+  during upsert. If data is sorted by frequently queried columns, queries will leverage parquet predicate pushdown 
+  to trim down the data to ensure lower latency as well.
+  
+- Additionally, parquet writing is quite a memory intensive operation. When writing large volumes of data into a table 
+  that is also partitioned into 1000s of partitions, without sorting of any kind, the writer may have to keep 1000s of 
+  parquet writers open simultaneously incurring unsustainable memory pressure and eventually leading to crashes.
+  
+- It's also desirable to start with the smallest amount of files possible when bulk importing data, as to avoid 
+  metadata overhead later on for writers and queries. 
+
+3 Sort modes supported out of the box are: `PARTITION_SORT`,`GLOBAL_SORT` and `NONE`.
+
+## Configurations 
+One can set the config [“hoodie.bulkinsert.sort.mode”](https://hudi.apache.org/docs/configurations.html#withBulkInsertSortMode) to either 
+of the three values, namely NONE, GLOBAL_SORT and PARTITION_SORT. Default sort mode is `GLOBAL_SORT`.
+
+## Different Sort Modes
+
+### Global Sort
+
+As the name suggests, Hudi sorts the records globally across the input partitions, which maximizes the number of files 

Review Comment:
   hudi sorts the records globally by which column? recordKey?



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