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Subject [GitHub] [hadoop] steveloughran commented on a change in pull request #2801: HADOOP-17597. Optionally downgrade on S3A Syncable calls
Date Thu, 22 Apr 2021 18:47:35 GMT

steveloughran commented on a change in pull request #2801:
URL: https://github.com/apache/hadoop/pull/2801#discussion_r618655930



##########
File path: hadoop-tools/hadoop-aws/src/site/markdown/tools/hadoop-aws/troubleshooting_s3a.md
##########
@@ -1036,6 +1036,39 @@
 This includes resilient logging, HBase-style journaling
 and the like. The standard strategy here is to save to HDFS and then copy to S3.
 
+### <a name="syncable"></a> `UnsupportedOperationException` "S3A streams are
not Syncable. See HADOOP-17597."
+
+The application has tried to call either the `Syncable.hsync()` or `Syncable.hflush()`
+methods on an S3A output stream. This has been rejected because the
+connector isn't saving any data at all. The `Syncable` API, especially the
+`hsync()` call, are critical for applications such as HBase to safely
+persist data.
+
+The S3A connector throws an `UnsupportedOperationException` when these API calls
+are made, because the guarantees absolutely cannot be met: nothing is being flushed
+or saved.
+
+* Applications which intend to invoke the Syncable APIs call `hasCapability("hsync")` on
+  the stream to see if they are supported.
+* Or catch and downgrade `UnsupportedOperationException`.
+
+These recommendations _apply to all filesystems_. 
+
+To downgrade the S3A connector to simplying warning of the use of

Review comment:
       fixed




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