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List:       postgresql-general
Subject:    Re: [GENERAL] Vacuum Full - Questions
From:       Venkata B Nagothi <nag1010 () gmail ! com>
Date:       2016-08-31 23:53:38
Message-ID: CAEyp7J-qYvquD3TrQEBNsJ0TDJPSvS7WYv-qyUCEhFinN_bnrQ () mail ! gmail ! com
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On Thu, Sep 1, 2016 at 8:41 AM, Patrick B <patrickbakerbr@gmail.com> wrote:

> Hi guys,
>
> A dev has ran a VACUUM FULL command into our test database running
> PostgreSQL 9.5 (I know... goddamn!!!!)...
>
> ... after the Vacuum Full, some queries start using SEQ scans instead of
> indexes...
>
> Does that happen because of the size of the table? The table that I'm
> referring to is 150MB big after the vacuum (Before was 1G)...
>

Yes, it is possible that sequential scans after vacuum full are cheaper
than Index scans before vacuum full ? do you see improvement in query
response times ?
How does the cost differ ?

Regards,
Venkata B N

Fujitsu Australia

[Attachment #3 (text/html)]

<div dir="ltr"><div class="gmail_extra"><br><div class="gmail_quote">On Thu, Sep 1, \
2016 at 8:41 AM, Patrick B <span dir="ltr">&lt;<a \
href="mailto:patrickbakerbr@gmail.com" \
target="_blank">patrickbakerbr@gmail.com</a>&gt;</span> wrote:<br><blockquote \
class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc \
solid;padding-left:1ex"><div dir="ltr">Hi guys,<div><br></div><div>A dev has ran a \
VACUUM FULL command into our test database running PostgreSQL 9.5 (I know... \
goddamn!!!!)...</div><div><br></div><div>... after the Vacuum Full, some queries \
start using SEQ scans instead of indexes...</div><div><br></div><div>Does that happen \
because of the size of the table? The table that I&#39;m referring to is 150MB big \
after the vacuum (Before was 1G)...</div></div></blockquote><div><br></div><div>Yes, \
it is possible that sequential scans after vacuum full are cheaper than Index scans \
before vacuum full ? do you see improvement in query response times ?  </div><div>How \
does the cost differ ?</div><div><br></div><div>Regards,</div><div>Venkata B \
N</div><div><br></div><div>Fujitsu Australia</div></div></div></div>



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