[GitHub] [iceberg] szehon-ho commented on a change in pull request #4223: Docs: Clarify merge-on-read modes in docs for spark

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szehon-ho commented on a change in pull request #4223:
URL: https://github.com/apache/iceberg/pull/4223#discussion_r814996711



##########
File path: docs/versioned/spark/spark-writes.md
##########
@@ -98,6 +98,11 @@ WHEN NOT MATCHED AND s.event_time > still_valid_threshold THEN INSERT (id, count
 
 Only one record in the source data can update any given row of the target table, or else an error will be thrown.
 
+!!! Note
+    By default Spark uses copy-on-write merge mode.
+    With spark-3.2 and onwards, iceberg supports merge-on-read mode.    

Review comment:
       Not sure what everyone thinks, but seems there's not much context.  Should we explain what it means (that it writes v2 delete files)?

##########
File path: docs/versioned/spark/spark-writes.md
##########
@@ -98,6 +98,11 @@ WHEN NOT MATCHED AND s.event_time > still_valid_threshold THEN INSERT (id, count
 
 Only one record in the source data can update any given row of the target table, or else an error will be thrown.
 
+!!! Note
+    By default Spark uses copy-on-write merge mode.
+    With spark-3.2 and onwards, iceberg supports merge-on-read mode.    
+    To use merge-on-read merge mode, need to set the table property `write.merge.mode` to "merge-on-read".

Review comment:
       Do we need to add that format-version needs to be v2?
   
   Also nit: I think 'need to' is redundant, removing it seems more consistent with the rest of docs

##########
File path: docs/versioned/spark/spark-writes.md
##########
@@ -98,6 +98,11 @@ WHEN NOT MATCHED AND s.event_time > still_valid_threshold THEN INSERT (id, count
 
 Only one record in the source data can update any given row of the target table, or else an error will be thrown.
 
+!!! Note

Review comment:
       Does the three !!! renders anything?  (I dont see it when viewing the file as md).  Should we just use a normal sub-header here?




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