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From "Vitalii Diravka (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DRILL-5660) Drill 1.10 queries fail due to Parquet Metadata "corruption" from DRILL-3867
Date Tue, 11 Jul 2017 12:08:00 GMT

    [ https://issues.apache.org/jira/browse/DRILL-5660?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16082118#comment-16082118
] 

Vitalii Diravka commented on DRILL-5660:
----------------------------------------

[~paul-rogers] 
I agree with update the metadata file version number, the older Drillbits will throw more
clear message with a reason of failing. 
Also I am going to implement two things: 
1. Ignoring metadata cache file if it has newer version number. And then to proceed of performing
the query without reading of the metadata cache files as you suggested in [comment for DRILL-4139|https://issues.apache.org/jira/browse/DRILL-4139?focusedCommentId=16080914&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-16080914]
2. Adding a minor version for parquet metadata. For the case, when the structure of metadata
file isn't changed, but values are different (like here) to inherit the last metadata cache
file (not abstract base class). It will allow to avoid of a lot duplicated code. 
If the structure of the metadata file is changed, the major version should be updated.

> 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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