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https://issues.apache.org/jira/browse/SPARK-32778?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17191468#comment-17191468
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Hyukjin Kwon commented on SPARK-32778:
--------------------------------------
Spark 2.3 is EOL too .. can you reproduce in Spark 2.4 or 3.0?
> Accidental Data Deletion on calling saveAsTable
> -----------------------------------------------
>
> Key: SPARK-32778
> URL: https://issues.apache.org/jira/browse/SPARK-32778
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 2.2.0
> Reporter: Aman Rastogi
> Priority: Major
>
> {code:java}
> df.write.option("path",
> "/already/existing/path").mode(SaveMode.Append).format("json").saveAsTable(db.table)
> {code}
> Above code deleted the data present in path "/already/existing/path". This
> happened because table was already not there in hive metastore however, path
> given had data. And if table is not present in Hive Metastore, SaveMode gets
> modified internally to SaveMode.Overwrite irrespective of what user has
> provided, which leads to data deletion. This change was introduced as part of
> https://issues.apache.org/jira/browse/SPARK-19583.
> Now, suppose if user is not using external hive metastore (hive metastore is
> associated with a cluster) and if cluster goes down or due to some reason
> user has to migrate to a new cluster. Once user tries to save data using
> above code in new cluster, it will first delete the data. It could be a
> production data and user is completely unaware of it as they have provided
> SaveMode.Append or ErrorIfExists. This will be an accidental data deletion.
>
> Repro Steps:
>
> # Save data through a hive table as mentioned in above code
> # create another cluster and save data in new table in new cluster by giving
> same path
>
> Proposed Fix:
> Instead of modifying SaveMode to Overwrite, we should modify it to
> ErrorIfExists in class CreateDataSourceTableAsSelectCommand.
> Change (line 154)
>
> {code:java}
> val result = saveDataIntoTable(
> sparkSession, table, tableLocation, child, SaveMode.Overwrite, tableExists =
> false)
>
> {code}
> to
>
> {code:java}
> val result = saveDataIntoTable(
> sparkSession, table, tableLocation, child, SaveMode.ErrorIfExists,
> tableExists = false){code}
> This should not break CTAS. Even in case of CTAS, user may not want to delete
> data if already exists as it could be accidental.
>
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