[jira] [Resolved] (HIVE-18098) Add support for Export/Import for Acid tables

["Eugene Koifman (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HIVE-18098?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Eugene Koifman resolved HIVE-18098.
-----------------------------------
       Resolution: Done
    Fix Version/s: 3.1.0
     Release Note: n/a

done in HIVE-18739

> Add support for Export/Import for Acid tables
> ---------------------------------------------
>
>                 Key: HIVE-18098
>                 URL: https://issues.apache.org/jira/browse/HIVE-18098
>             Project: Hive
>          Issue Type: New Feature
>          Components: Transactions
>            Reporter: Eugene Koifman
>            Assignee: Eugene Koifman
>            Priority: Major
>             Fix For: 3.1.0
>
>
> How should this work?
> For regular tables export just copies the files under table root to a specified directory.
> This doesn't make sense for Acid tables:
> * Some data may belong to aborted transactons
> * Transaction IDs are imbedded into data/files names.  You'd have export delta/ and base/ each of which may have files with the same names, e.g. bucket_00000.   
> * On import these IDs won't make sense in a different cluster or even a different table (which may have delta_x_x for example for the same x (but different data of course).
> * Export creates a _metadata column types, storage format, etc.  Perhaps it can include info about aborted IDs (if the whole file can't be skipped).
> * Even importing into the same table on the same cluster may be a problem.  For example delta_5_5/ existed at the time of export and was included in the export.  But 2 days later it may not exist because it was compacted and cleaned.
> * If importing back into the same table on the same cluster, the data could be imported into a different transaction (assuming per table writeIDs) w/o having to remap the IDs in the rows themselves.
> * support Import Overwrite?
> * Support Import as a new txn with remapping of ROW_IDs?  The new writeID can be stored in a delta_x_x/_meta_data and ROW__IDs can be remapped at read time (like isOriginal) and made permanent by compaction.
> * It doesn't seem reasonable to import acid data into non-acid table
> Perhaps import can work similar to Load Data: look at the file imported, if it has Acid columns, leave a note in the delta_x_x/_meta_data to indicate that these columns should be skipped a new ROW_IDs assigned at read time.
> h3. Case I
> Table has delta_7_7 and delta_8_8.  Sine both may have bucket_0000, we could export to export_dir and rename files as bucket_0000 and bucket_0000_copy_1.  Load Data supports input dir with copy_N files.
> h3. Case II
> what if we have delete_delta_9_9 in the source.  Now you can't just ignore ROW_IDs after import.
> * -Only export the latest base_N?  Or more generally up to the smallest deleted ROW_ID (which may be hard to find w/o scanning all deletes.  The export then would have to be done under X lock to prevent new concurrent deletes)-
> * Stash all deletes in some additional file file which on import gets added into the target delta/ so that Acid reader can apply them to the data in this delta/ but so that they don't clash with 'normal' deletes that exist in the table.
> ** here we may also have multiple delete_delta/ with identical file names.  Does delete delta reader handle copy_N files?



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