Shant Hovsepian created IMPALA-10327:
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Summary: SymlinkTextInputFormat for reading manifest file based
tables.
Key: IMPALA-10327
URL: https://issues.apache.org/jira/browse/IMPALA-10327
Project: IMPALA
Issue Type: New Feature
Components: Catalog, Frontend
Reporter: Shant Hovsepian
The
[SymlinkTextInputFormat|https://github.com/apache/hive/blob/master/ql/src/java/org/apache/hadoop/hive/ql/io/SymlinkTextInputFormat.java]
was an early Hadoop/Hive feature that has recently started to see lots of use.
Originally it was used to support symlinks in hive warehouse directories but
now it's more commonly used as a way to support specifying the files that make
up a hive table without requiring a directory listing operation.
Instead of pointing to a directory of files or partitions the Hive table
metadata refers to a single directory containing "manifest files", these files
have a well defined format which specifies the files that constitute the table.
This mechanism is used by in the following cases.
* Delta Lakes uses manifest to generate consistent read-only views of its
table format for use by Presto, Hive, and Redshift Spectrum
[https://docs.delta.io/0.7.0/integrations.html]
* AWS Redshift can UNLOAD Redshift tables and partitions to corresponding
parquets files on S3 for consumption by other tools:
[https://docs.aws.amazon.com/redshift/latest/dg/loading-data-files-using-manifest.html]
* AWS S3 Inventories:
[https://docs.aws.amazon.com/AmazonS3/latest/dev/storage-inventory.html]
Using the functionality with HDFS and S3 even without the need to interop with
the above would provider performance benefits by avoiding expensive directory
listing operations.
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