[jira] [Resolved] (OAK-2725) Wrong indexed query estimates exceed more than double the actual index entries

["Thomas Mueller (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/OAK-2725?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Thomas Mueller resolved OAK-2725.
---------------------------------
    Resolution: Won't Fix

> Wrong indexed query estimates exceed more than double the actual index entries
> ------------------------------------------------------------------------------
>
>                 Key: OAK-2725
>                 URL: https://issues.apache.org/jira/browse/OAK-2725
>             Project: Jackrabbit Oak
>          Issue Type: Bug
>          Components: query
>    Affects Versions: 1.1.8
>            Reporter: Florin Iordache
>            Priority: Critical
>             Fix For: 1.2
>
>         Attachments: OAK-2725-test.patch
>
>
> The {{ApproximateCounter.adjustCountSync}} public method that is used by the indexing engine will sometimes produce very unrealistic cost estimates. 
> The problem is that it can produce an estimated cost that exceeds the estimated cost of the full traversal query, thus causing the index to be bypassed altogether, resulting in a full traversal rather than the use of the existing index.
> Problem resides in the way the property counts are updated:
> * The count property update goes through if two randoms are equal to zero: random(100) and random({1, 2, 4, 8, 16, ...}).
> * Same static pseudo random generator for all invocations.
> Even if #1 might seem improbable, it is statistically possible to reach a very high count with only a handful of invocations.
> In practice I've found that running 100 tests with 1000 invocations if the adjustCountSync method will yield costs exceeding value 2000 in 4-10% of the tests. Attaching a patch for {{ApproximateCounterTest}} with this test case.



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