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https://issues.apache.org/jira/browse/HIVE-11525?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15224599#comment-15224599
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Gopal V commented on HIVE-11525:
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bq. The code parses only the hdfs file path name (hDFS directory read), not its
contents.
The code is too late to prevent a getBlockLocations or getFileStatus on the
pruned files, so the pruning happens after the file existence has been
established (would like to be earlier, but most input formats accept a
directory as a whole and this needs to be a PathFilter predicate to list dirs).
> Bucket pruning
> --------------
>
> Key: HIVE-11525
> URL: https://issues.apache.org/jira/browse/HIVE-11525
> Project: Hive
> Issue Type: Improvement
> Components: Logical Optimizer
> Affects Versions: 0.13.0, 0.14.0, 0.13.1, 1.0.0, 1.2.0, 1.1.0, 1.3.0, 2.0.0
> Reporter: Maciek Kocon
> Assignee: Gopal V
> Labels: TODOC2.0
> Fix For: 2.0.0
>
> Attachments: HIVE-11525.1.patch, HIVE-11525.2.patch,
> HIVE-11525.3.patch, HIVE-11525.WIP.patch
>
>
> Logically and functionally bucketing and partitioning are quite similar -
> both provide mechanism to segregate and separate the table's data based on
> its content. Thanks to that significant further optimisations like
> [partition] PRUNING or [bucket] MAP JOIN are possible.
> The difference seems to be imposed by design where the PARTITIONing is
> open/explicit while BUCKETing is discrete/implicit.
> Partitioning seems to be very common if not a standard feature in all current
> RDBMS while BUCKETING seems to be HIVE specific only.
> In a way BUCKETING could be also called by "hashing" or simply "IMPLICIT
> PARTITIONING".
> Regardless of the fact that these two are recognised as two separate features
> available in Hive there should be nothing to prevent leveraging same existing
> query/join optimisations across the two.
> BUCKET pruning
> Enable partition PRUNING equivalent optimisation for queries on BUCKETED
> tables
> Simplest example is for queries like:
> "SELECT … FROM x WHERE colA=123123"
> to read only the relevant bucket file rather than all file-buckets that
> belong to a table.
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