[jira] [Reopened] (SOLR-6968) add hyperloglog in statscomponent as an approximate count

["Hoss Man (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/SOLR-6968?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Hoss Man reopened SOLR-6968:
----------------------------

Doing some perf testing, i found that the SPARSE representation of HLL can cause some heinous response times for large sets -- a minor part of the issue seems to be the slower insertion rate compared to the FULL representation (documented), but a much bigger factor is that _merging_ multiple (large) SPARSE HLLs is almost 10x slower then merging FULL HLLs of the same size.

it might be worth adding tuning options and/or hueristics to control if/when SPARSE representation should be used (in cases where folks have smaller sets and care more about memory then speed), but for now i'm just going disable it.

> add hyperloglog in statscomponent as an approximate count
> ---------------------------------------------------------
>
>                 Key: SOLR-6968
>                 URL: https://issues.apache.org/jira/browse/SOLR-6968
>             Project: Solr
>          Issue Type: Sub-task
>            Reporter: Hoss Man
>            Assignee: Hoss Man
>             Fix For: Trunk, 5.2
>
>         Attachments: SOLR-6968.patch, SOLR-6968.patch, SOLR-6968.patch, SOLR-6968.patch, SOLR-6968.patch, SOLR-6968.patch
>
>
> stats component currently supports "calcDistinct" but it's terribly inefficient -- especially in distib mode.
> we should add support for using hyperloglog to compute an approximate count of distinct values (using localparams via SOLR-6349 to control the precision of the approximation)



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