[GitHub] HeartSaVioR commented on a change in pull request #18410: [SPARK-20971][SS] purge metadata log in FileStreamSource

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HeartSaVioR commented on a change in pull request #18410: [SPARK-20971][SS] purge metadata log in FileStreamSource
URL: https://github.com/apache/spark/pull/18410#discussion_r258358837
 
 

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 File path: sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/FileStreamSource.scala
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 @@ -256,8 +259,9 @@ class FileStreamSource(
    * equal to `end` and will only request offsets greater than `end` in the future.
    */
   override def commit(end: Offset): Unit = {
-    // No-op for now; FileStreamSource currently garbage-collects files based on timestamp
-    // and the value of the maxFileAge parameter.
+    if (currentLogOffset > minBatchesToRetain) {
+      metadataLog.purge(currentLogOffset - minBatchesToRetain)
 
 Review comment:
   HDFSMetadataLog is not aware of such configuration.
   
   Btw, I've put my observation on `CompactibleFileStreamLog.purge()` in comment on SPARK-20971. 
   
   https://issues.apache.org/jira/browse/SPARK-20971?focusedCommentId=16772632&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-16772632
   
   Let me quote it here:
   
   > Btw, calling `purge` breaks CompactibleFileStreamLog since CompactibleFileStreamLog expects non-compacted batches to be exist, but `purge` just removes all of metadata files matching criteria. The safest way seems to be just disallowing `purge` for CompactibleFileStreamLog, otherwise we have to concern about the intention of calling `purge`, like I was curious of rationalization of this issue like above.
   
   So I've got a feeling that this may bring unexpected behavior and should be avoided.

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