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https://issues.apache.org/jira/browse/DRILL-5660?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16087394#comment-16087394
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ASF GitHub Bot commented on DRILL-5660:
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Github user paul-rogers commented on the issue:
https://github.com/apache/drill/pull/877
I wonder if you are very close to solving another long-running problem in
Drill: Parquet metadata file corruption (or, at least, the corruption causing
queries to fail.)
We have an issue that two Drillbits can write to metadata file concurrently
and corrupt it. We also have a case where Drillbit A writes the file while
Drillbit B reads it. In both cases, the reading Drillbit can't deserialize the
file and "bad things happen."
We need code that can try to deserialize a file, notice that the JSON in
the file does not fit our schema, and handle the deserialization exception. If
we do that, it is a small step to ignore all forms of read errors:
file-not-found, file truncation, etc.
In this case, we give an explicit version error if we can read the file and
it has the wrong version. If we can't deserialize the file, we log an error
about "file is of a newer version or corrupt."
After this, the corruption can still occur, but the user view is that
queries run slow instead of just failing.
> Drill 1.10 queries fail due to Parquet Metadata "corruption" from DRILL-3867
> ----------------------------------------------------------------------------
>
> Key: DRILL-5660
> URL: https://issues.apache.org/jira/browse/DRILL-5660
> Project: Apache Drill
> Issue Type: Bug
> Affects Versions: 1.11.0
> Reporter: Paul Rogers
> Assignee: Vitalii Diravka
> Fix For: 1.11.0
>
>
> Drill recently accepted a PR for the following bug:
> DRILL-3867: Store relative paths in metadata file
> This PR turned out to have a flaw which affects version compatibility.
> The DRILL-3867 PR changed the format of Parquet metadata files to store
> relative paths. All Drill servers after that PR create files with relative
> paths. But, the version number of the file is unchanged, so that older
> Drillbits don't know that they can't understand the file.
> Instead, if an older Drill tries to read the file, queries fail left and
> right. Drill will resolve the paths, but does so relative to the user's HDFS
> home directory, which is wrong.
> What should have happened is that we should have bumped the parquet metadata
> file version number so that older Drillbits can’t read the file. This ticket
> requests that we do that.
> Now, one could argue that the lack of version number change is fine. Once a
> user upgrades Drill, they won't use an old Drillbit. But, things are not that
> simple:
> * A developer tests a branch based on a pre-DRILL-3867 build on a cluster in
> which metadata files have been created by a post-DRILL-3867 build. (This has
> already occurred multiple times in our shop.)
> * A user tries to upgrade to Drill 1.11, finds an issue, and needs to roll
> back to Drill 1.10. Doing so will cause queries to fail due to
> seemingly-corrupt metadata files.
> * A user tries to do a rolling upgrade: running 1.11 on some servers, 1.10 on
> others. Once a 1.11 server is installed, the metadata is updated ("corrupted"
> from the perspective of 1.10) and queries fail.
> Standard practice in this scenario is to:
> * Bump the file version number when the file format changes, and
> * Software refuses to read files with a version newer than the software was
> designed for.
> Of course, it is highly desirable that newer servers read old files, but that
> is not the issue here.
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