Re: BUG #13908: Query returns too few rows

From: "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: "pgsql-bugs(at)postgresql(dot)org" <pgsql-bugs(at)postgresql(dot)org>, Seth P <seth-p(at)outlook(dot)com>
Subject: Re: BUG #13908: Query returns too few rows
Date: 2016-02-05 05:38:34
Message-ID: CAKFQuwY5L_45w+EDWn1KVadnpf5FdUT6mPGQinMv_2K3X4FYUQ@mail.gmail.com
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On Thu, Feb 4, 2016 at 10:17 PM, David G. Johnston <
david(dot)g(dot)johnston(at)gmail(dot)com> wrote:

> On Thu, Feb 4, 2016 at 9:47 PM, David G. Johnston <
> david(dot)g(dot)johnston(at)gmail(dot)com> wrote:
>
>> On this node's detail (the rows seems to appear consistently regardless
>> of node ordering in the plan...)
>> Hash (cost=1440572.59..1440572.59 rows=872393 width=24) (actual
>> time=151981.919..151981.919 rows=*1275138* loops=1)
>>
>
>
>> Bad Plan: ​
>>
>> ​ ​
>> Buckets: 131072 (originally 131072) Batches: 32 (originally 16) Memory
>> Usage: 3073kB
>>
>
> Final result: ​415,967 / ​416,075 (108 missing)
>

​So just over 3 output records per bucket and 32 batches ​gives 96+

>
>> ​Bad Plan: ​ Buckets: 65536 (originally 65536) Batches: 32 (originally
>> 16) Memory Usage: 3585kB
>>
>
> ​Final result: 415,874 / 416,075 (201 missing)​
>
>
​Just over 6 output records per bucket and 32 batches yields 192+

Didn't notice any obvious numeric equalities using ​
1,275,138

David J.

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