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From "Prasanth Jayachandran (JIRA)" <>
Subject [jira] [Updated] (HIVE-9689) Store distinct value estimator's bit vectors in metastore
Date Sun, 22 Mar 2015 17:50:12 GMT


Prasanth Jayachandran updated HIVE-9689:
    Labels: gsoc gsoc2015 hive java  (was: gsoc2015)

> Store distinct value estimator's bit vectors in metastore
> ---------------------------------------------------------
>                 Key: HIVE-9689
>                 URL:
>             Project: Hive
>          Issue Type: New Feature
>            Reporter: Prasanth Jayachandran
>              Labels: gsoc, gsoc2015, hive, java
> Hive currently uses PCSA (Probabilistic Counting and Stochastic Averaging) algorithm
to determine distinct cardinality. The NDV value determined from the UDF is stored in the
metastore instead of the actual bit vectors. This makes it impossible to estimate the overall
NDV across all the partitions (or selected partitions). We should ideally store the bitvectors
in the metastore and do server side merging of the bitvectors. Also we could replace the current
PCSA algorithm in favour of HyperLogLog if space is a constraint. 

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