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Posted to mapreduce-issues@hadoop.apache.org by "Ewan Higgs (JIRA)" <ji...@apache.org> on 2018/06/06 13:46:00 UTC
[jira] [Comment Edited] (MAPREDUCE-7101) Revisit behavior of JHS
scan file behavior
[ https://issues.apache.org/jira/browse/MAPREDUCE-7101?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16503311#comment-16503311 ]
Ewan Higgs edited comment on MAPREDUCE-7101 at 6/6/18 1:45 PM:
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{quote}integrate with cloud event sources which are set up to add a new event when a file is added to a container.
{quote}
While this might not be "fun" it might be the correct solution. Have the various cloud event sources (AWS Lambda, Google Cloud Functions, etc) been wrapped like S3/WASB/GCS, etc have been implemented as HCFSs? Is it required? Or do we just slurp up a kafka stream for the events and assume someone's made a bridge?
{quote}One thing to consider though: if the scanning includes subdirectories then listFiles(path, recursive=true) is orders of magnitude more efficient on S3A (and any other connector which can do bulk listings): we want to use that for any recursive polling.\{quote}
{quote}
HDFS-13616 (Batch listing of multiple directories) may also be relevant here for Hadoop.
was (Author: ehiggs):
{quote}integrate with cloud event sources which are set up to add a new event when a file is added to a container.\{quote}
While this might not be "fun" it might be the correct solution. Have the various cloud event sources (AWS Lambda, Google Cloud Functions, etc) been wrapped like S3/WASB/GCS, etc have been implemented as HCFSs? Is it required? Or do we just slurp up a kafka stream for the events and assume someone's made a bridge?
{quote}One thing to consider though: if the scanning includes subdirectories then listFiles(path, recursive=true) is orders of magnitude more efficient on S3A (and any other connector which can do bulk listings): we want to use that for any recursive polling.\{quote}
HDFS-13616 (Batch listing of multiple directories) may also be relevant here or Hadoop.
> Revisit behavior of JHS scan file behavior
> ------------------------------------------
>
> Key: MAPREDUCE-7101
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-7101
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Reporter: Wangda Tan
> Priority: Critical
>
> Currently, the JHS scan directory if the modification of *directory* changed:
> {code}
> public synchronized void scanIfNeeded(FileStatus fs) {
> long newModTime = fs.getModificationTime();
> if (modTime != newModTime) {
> <... omitted some logics ...>
> // reset scanTime before scanning happens
> scanTime = System.currentTimeMillis();
> Path p = fs.getPath();
> try {
> scanIntermediateDirectory(p);
> {code}
> This logic relies on an assumption that, the directory's modification time will be updated if a file got placed under the directory.
> However, the semantic of directory's modification time is not consistent in different FS implementations. For example, MAPREDUCE-6680 fixed some issues of truncated modification time. And HADOOP-12837 mentioned on S3, the directory's modification time is always 0.
> I think we need to revisit behavior of this logic to make it to more robustly work on different file systems.
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