[jira] [Updated] (PIG-5290) User Cache upload contention can cause job failures

["Erik Krogen (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/PIG-5290?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Erik Krogen updated PIG-5290:
-----------------------------
    Attachment: PIG-5290-1.patch

Thank you for the review [~rohini]!

I see you are right about (3); I missed the line you linked. I can keep it at the old behavior.

For (2), I agree that there is potential for collision during writing temp file, but figured that since it will fall back to default behavior if it had an error while uploading, this is not too much of an issue (just an extra JAR upload rather than using cache). I don't understand the "renaming to final file name" issue. Renames on HDFS overwrite, so if two users upload the same simultaneously, one of them will simply win (whoever comes second). Let me know if I am misunderstanding.

Sounds good on (4), thanks for the pointer.

Attaching v1 patch addressing your comments in (3), (4), comment in (1) is no longer relevant. Will wait on your response about (2).

> User Cache upload contention can cause job failures
> ---------------------------------------------------
>
>                 Key: PIG-5290
>                 URL: https://issues.apache.org/jira/browse/PIG-5290
>             Project: Pig
>          Issue Type: Bug
>    Affects Versions: 0.13.0
>            Reporter: Erik Krogen
>            Assignee: Erik Krogen
>         Attachments: PIG-5290-1.patch, PIG-5290.patch
>
>
> We recently enabled the User Cache (PIG-2672) feature and found that occasionally jobs would fail because of contention when uploading JARs into the cache. Although the cache is designed to be fail-safe, i.e. to fall back to normal behavior if anything goes wrong by catching all {{IOException}}, the portion of code which closes the output stream _is not_ wrapped within a {{try}} statement and thus an exception during the closing of that stream causes the entire job to fail. If multiple jobs are attempting to upload the same JAR failure simultaneously, the contention can cause this close statement to fail.
> The current strategy also has two other flaws. First, consider the scenario where job A begins uploading jar X. Job B also needs jar X, sees that the file exists, and launches its tasks. Yet, job A has not yet finished uploading jar X (perhaps it is large). So, the tasks are localizing a half-completed version of jar X. Second, the original design allowed for the same JAR (identical contents) to be shared between jobs even if a different name was used. In PIG-3815, however, this ability was removed, and now JARs are only shared if they have the same name.
> I propose we solve all of these issues simultaneously by returning to the listStatus based behavior (used prior to PIG-3815), but filter out entries ending in {{.tmp}}. When uploading, upload to {{randomNumber.tmp}}, then once the file is completed, do a rename to the original name of the JAR file. This ensures that incomplete files are never in a location that would be accessed by other jobs, and the only write operation accessing a shared path is a single rename operation.
> An alternative design is to use a single canonicalized name for all JAR files (they will still be unique since they are inside of directories based on their SHA1). Upload to a tmp file as previously described, then rename to the canonical name. This removes the need to do a listStatus call; however it will result in classpaths that are human unreadable since the name of the JAR file has been lost. I think it's worth it from a debugging standpoint to go with the first design.



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