[SPARK-23815][Core]Spark writer dynamic partition overwrite mode may fail to write output on multi level partition #20931
[SPARK-23815]follow up. add comment
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@@ -187,6 +187,13 @@ class HadoopMapReduceCommitProtocol( | |
| for (part <- partitionPaths) { | ||
| val finalPartPath = new Path(path, part) | ||
| if (!fs.delete(finalPartPath, true) && !fs.exists(finalPartPath.getParent)) { | ||
| // According to the official hadoop FileSystem API spec, delete op should assume | ||
| // the destination is no longer present regardless of return value, and in our case, | ||
| // it should return false only when finalPartPath does not exist. | ||
| // When finalPartPath does not exist, we need to take action only when the parent of | ||
| // finalPartPath does not exist(e.g. the scenario described on SPARK-23815), because | ||
| // FileSystem API spec on rename op says the rename destination must have a parent | ||
| // that exists, otherwise we may get unexpected result on the rename. | ||
| fs.mkdirs(finalPartPath.getParent) | ||
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Contributor
There was a problem hiding this comment. do you have some official HDFS document to support this change?
Author
There was a problem hiding this comment. @cloud-fan yes, in official HDFS document(https://hadoop.apache.org/docs/stable/hadoop-project-dist/hadoop-common/filesystem/filesystem.html), the rename command has precondition "dest must be root, or have a parent that exists" |
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| } | ||
| fs.rename(new Path(stagingDir, part), finalPartPath) | ||
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why we only create the parent dir if we fail to delete the
finalPartPath?Uh oh!
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@cloud-fan this is to follow the behavior of HDFS rename spec: it requires the parent to be present. If we create finalPartPath directly, then it will cause another wired behavior in rename when the dst path already exists. From the HDFS spec I shared above: " If the destination exists and is a directory, the final destination of the rename becomes the destination + the filename of the source path". We have confirmed this in our production cluster, and used the current patch to only create parent dir which follows the HDFS spec exactly,
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I think the problem here is we didn't check whether the
finalPartPathexists, and we shall actually check that before rename.There was a problem hiding this comment.
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I feel the code here is not safe. We may fail to delete if
finalPartPathdoesn't exist, or there are some real failures. We should make surefinalPartPathdoesn't exist before renaming.There was a problem hiding this comment.
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BTW we should add comments around here to explain all these stuff.
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+1 on add comments.
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The FileSystem API spec on delete says "Code SHOULD just call delete(path, recursive) and assume the destination is no longer present". Referring to its detailed spec, the only case that we may get false from delete would be
finalPartPathdoes not exist. Other failures should result in exception. WhenfinalPartPathdoes not exist, which is an expected case, we only need action if the parent offinalPartPathdoes not exist because otherwise we will have problem in rename according to rename spec. Please advise if you guys think we still should double-checkfinalPartPathbefore rename. will add comment after the discussionThere was a problem hiding this comment.
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ah makes sense, let's add some comment to summary these discussions.
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added