arina-ielchiieva commented on a change in pull request #1953: Add docs for Drill Metastore URL: https://github.com/apache/drill/pull/1953#discussion_r374643271
########## File path: _docs/performance-tuning/drill-metastore/030-drill-iceberg-metastore.md ########## @@ -0,0 +1,69 @@ +--- +title: "Drill Iceberg Metastore" +parent: "Drill Metastore" +date: 2020-01-31 +--- + +Drill uses Iceberg Metastore implementation based on [Iceberg tables](http://iceberg.incubator.apache.org). For Drill 1.17, + this is default Drill Metastore implementation. For details on how to configure Iceberg Metastore implementation and + its option descriptions, please refer to [Iceberg Metastore docs](https://github.com/apache/drill/blob/master/metastore/iceberg-metastore/README.md). + +{% include startnote.html %} +Iceberg table supports concurrent writes and transactions but they are only effective on file systems that support + atomic rename. +If the file system does not support atomic rename, it could lead to inconsistencies during concurrent writes. +{% include endnote.html %} + +### Iceberg Tables Location + +Iceberg tables will reside on the file system in the location based on +Iceberg Metastore base location `drill.metastore.iceberg.location.base_path` and component specific location. +If Iceberg Metastore base location is `/drill/metastore/iceberg` +and tables component location is `tables`. Iceberg table for tables component +will be located in `/drill/metastore/iceberg/tables` folder. + +Metastore metadata will be stored inside Iceberg table location provided +in the configuration file. Drill table metadata location will be constructed +based on specific component storage keys. For example, for `tables` component, +storage keys are storage plugin, workspace and table name: unique table identifier in Drill. + +Assume Iceberg table location is `/drill/metastore/iceberg/tables`, metadata for the table +`dfs.tmp.nation` will be stored in the `/drill/metastore/iceberg/tables/dfs/tmp/nation` folder. + +Example of base Metastore configuration file `drill-metastore-override.conf`, where Iceberg tables will be stored in + hdfs: + +``` +drill.metastore.iceberg: { + config.properties: { + fs.defaultFS: "hdfs:///" + } + + location: { + base_path: "/drill/metastore", + relative_path: "iceberg" + } +} +``` + +### Metadata Storage Format + +Iceberg tables support data storage in three formats: Parquet, Avro, ORC. Drill metadata will be stored in Parquet files. +This format was chosen over others since it is column oriented and efficient in terms of disk I/O when specific +columns need to be queried. + +Each Parquet file will hold information for one partition. Partition keys will depend on Metastore +component characteristics. For example, for tables component, partitions keys are storage plugin, workspace, +table name and metadata key. + +Parquet files name will be based on UUID to ensure uniqueness. If somehow collision occurs, modify operation +in Metastore will fail. + +### Iceberg metadata expiration + +Iceberg table generates metadata for each modification operation: +snapshot, manifest file, table metadata file. Also when performing delete operation, +previously stored data files are not deleted. These files with the time can occupy lots of space. +Two table properties `write.metadata.delete-after-commit.enabled` and `write.metadata.previous-versions-max` +control expiration process. Metadata files will be expired automatically if +`write.metadata.delete-after-commit.enabled` is enabled. Review comment: As long as Iceberg is used on fs that supports atomic renames, all concurrency stuff is handled by Iceberg. > Therefore Iceberg requires that Drill periodically remove old file versions. Drill does this on a time interval defined by .... Yes, all Drill is need to do is just to define the interval, everything else is handled by Iceberg library internally. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: [email protected] With regards, Apache Git Services
