[jira] [Updated] (CALCITE-6704) Add limit parameter to restrict the result size of UniqueKeys metadata

["ASF GitHub Bot (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CALCITE-6704?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

ASF GitHub Bot updated CALCITE-6704:
------------------------------------
    Labels: pull-request-available  (was: )

> Add limit parameter to restrict the result size of UniqueKeys metadata
> ----------------------------------------------------------------------
>
>                 Key: CALCITE-6704
>                 URL: https://issues.apache.org/jira/browse/CALCITE-6704
>             Project: Calcite
>          Issue Type: Improvement
>          Components: core
>    Affects Versions: 1.38.0
>            Reporter: Stamatis Zampetakis
>            Assignee: Stamatis Zampetakis
>            Priority: Major
>              Labels: pull-request-available
>
> In some cases, the number of unique keys grows exponentially for certain relational expressions.
> Consider a table with a composite key \{k1, k2, k3\} and the following query:
> {code:sql}
> SELECT k1, k1, k2, k2, k3, k3 FROM composite
> {code}
> The number of minimal unique keys for this query is 2^3:
> {noformat}
> {0, 2, 4}, {0, 3, 4}, {1, 2, 4}, {1, 3, 4}, {0, 2, 5}, {0, 3, 5}, {1, 2, 5}, {1, 3, 5}
> {noformat}
> In this case, the size of *minimal keys* is exponential to the number of columns in the composite key. The number of keys is f(x,y) = x^y where _x_ is the number of repetitions of each column and _y_ is the number of columns in the composite key. The example is taken out from CALCITE-6640.
> A large number of unique keys may occur in other use-cases as well. Computing the entire result set may become prohibitively expensive and cause OOM and other failures. 
> To prevent this from happening we propose to add a new  parameter to the UniqueKeys  interface allowing the users to specify a limit on the size of the result set.



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