[
https://issues.apache.org/jira/browse/DRILL-5660?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Arina Ielchiieva updated DRILL-5660:
------------------------------------
Labels: doc-impacting ready-to-commit (was: doc-impacting)
> 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
> Labels: doc-impacting, ready-to-commit
> Fix For: 1.12.0
>
>
> 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.
> *Main technical points of working of parquet metadata caching for now.*
> Only process of reading the parquet metadata is changed (the process of
> writing isn't changed):
> +1. Metadata files are valid:+
> Metadata objects are created by deserialization of parquet metadata files in
> the process of creating ParquetGroupScan physical operator.
> All supported versions are stored in the "MetadataVersion.Constants" class
> and in the Jackson annotations for Metadata.ParquetTableMetadataBase class.
> +2. Metadata files version isn't supported (created by newer Drill version).
> Drill table has at least one metadata file of unsupported version:+
> JsonMappingException is obtained and swallowed without creating metadata
> object. Error message is logged. The state is stored in MetadataContext,
> therefore further there will be no attempt to deserialize metadata file again
> in context of performing current query. The physical plan will be created
> without using parquet metadata caching. Warning message is logged for every
> further check "is metadata corrupted".
> +3. Drill table has at least one corrupted metadata file, which can't be
> deserialized:+
> JsonParseException is obtained. Then the same behaviour as for the
> unsupported version files.
> +4. The metadata file was removed by other process:+
> FileNotFound is obtained. Then the same behaviour as for the unsupported
> version files.
> The new versions of metadata should be added in such manner:
> 1. Increasing of the metadata major version if metadata structure is changed.
> 2. Increasing of the metadata minor version if only metadata content is
> changed, but metadata structure is the same.
> For the first case a new metadata structure (class) should be created
> (possible an improvement of deserializing metadata files of any version into
> one strucure by using special converting)
> For the second case only annotation for the last metadata structure can be
> updated.
> *Summary*
> 1. Drill will read and use metadata files if files are valid, all present and
> supported. Under supported we mean that files were created before and under
> current Drill version.
> 2. Drill will ignore reading metadata files if at least one file is missing,
> empty, corrupted or unsupported. Under unsupported we mean files created
> after current Drill version. When metadata files are not used, warning
> message will be written to the logs.
--
This message was sent by Atlassian JIRA
(v6.4.14#64029)
