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From "Eugene Koifman (Jira)" <>
Subject [jira] [Assigned] (HIVE-17328) Remove special handling for Acid tables wherever possible
Date Wed, 28 Jul 2021 14:14:04 GMT


Eugene Koifman reassigned HIVE-17328:

    Assignee:     (was: Eugene Koifman)

> Remove special handling for Acid tables wherever possible
> ---------------------------------------------------------
>                 Key: HIVE-17328
>                 URL:
>             Project: Hive
>          Issue Type: Improvement
>          Components: Transactions
>            Reporter: Eugene Koifman
>            Priority: Major
> There are various places in the code that do something like 
> {noformat}
> if(acid update or delete) {
>  do something
> }
> else {
> do something else
> }
> {noformat}
> this complicates the code and makes it so that acid code path is not properly tested
in many new non-acid features or bug fixes.
> Some work to simplify this was done in HIVE-15844.
> _SortedDynPartitionOptimizer_ has some special logic
> _ReduceSinkOperator_ relies on partitioning columns for update/delete be _UDFToInteger(RecordIdentifier)_
which is set up in _SemanticAnalyzer_.  Consequently _SemanticAnalyzer_ has special logic
to set it up.
> _FileSinkOperator_ has some specialization.
> _AbstractCorrelationProcCtx_ makes changes specific to acid writes setting hive.optimize.reducededuplication.min.reducer=1
> With acid 2.0 (HIVE-17089) a lot more of it can simplified/removed.
> Generally, Acid Insert follows the same code path as regular insert except that the writer
in _FileSinkOperator_ is Acid specific.
> So all the specialization is to route Update/Delete events to the right place.
> We can do the U=D+I early in the operator pipeline so that an Update is a Hive multi-insert
with 1 leg being the Insert leg and the other being the Delete leg (like Merge stmt).
> The Delete events themselves don't need to be routed in any particular way if we always
ship all delete_delta files for each split.  This is ok since delete events are very small
and highly compressible.  What is shipped is independent of what needs to be loaded into memory.
> This would allow removing almost all special code paths.
> If need be we can also have the compactor rewrite the delete files so that the name of
the file matches the contents and make it as if they were bucketed properly and use it reduce
what needs to be shipped for each split.  This may help with some extreme cases where someone
updates 1B rows.
> This would in particular allow DISTRIBUTE BY for update/delete
> Is this currently supported for Acid insert?

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