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ASF GitHub Bot commented on DRILL-5660: --------------------------------------- Github user arina-ielchiieva commented on a diff in the pull request: https://github.com/apache/drill/pull/877#discussion_r132405399 --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/store/parquet/ParquetGroupScan.java --- @@ -268,11 +276,15 @@ private FileSelection expandIfNecessary(FileSelection selection) throws IOExcept // use the cacheFileRoot if provided (e.g after partition pruning) Path metaFilePath = new Path(cacheFileRoot != null ? cacheFileRoot : selectionRoot, Metadata.METADATA_FILENAME); if (!fs.exists(metaFilePath)) { // no metadata cache + MetadataContext metaContext = selection.getMetaContext(); + if (metaContext != null) { + // some metadata files are absent, but some are present (since metadata context was created) + metaContext.isMetadataFilesMissingOrCorrupted = true; --- End diff -- Please use setter & getter instead of direct assignment / access. > 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 > 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)