Subject: Re: Re: COPY FREEZE and setting PD_ALL_VISIBLE/visibility map bits
To: Pavan Deolasee <pavan.deolasee@gmail.com>
Cc: Masahiko Sawada <sawada.mshk@gmail.com>,
 pgsql-hackers <pgsql-hackers@postgresql.org>,
 Jeff Janes <jeff.janes@gmail.com>, Simon Riggs <simon@2ndquadrant.com>
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From: David Steele <david@pgmasters.net>
Message-ID: <ff4c55c4-ac5b-e709-87c2-915cf14221f3@pgmasters.net>
Date: Wed, 20 Mar 2019 14:30:53 +0400
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Hi Pavan,

On 3/14/19 2:20 PM, Masahiko Sawada wrote:
> On Thu, Mar 14, 2019 at 5:17 PM Pavan Deolasee <pavan.deolasee@gmail.com> wrote:
>>
>> Ok. I will run some tests. But please note that this patch is a bug fix to address the performance issue that is caused by having to rewrite the entire table when all-visible bit is set on the page during first vacuum. So while we may do some more work during COPY FREEZE, we're saving a lot of page writes during next vacuum. Also, since the scan that we are doing in this patch is done on a page that should be in the buffer cache, we will pay a bit in terms of CPU cost, but not anything in terms of IO cost.
> 
> Agreed. I had been misunderstanding this patch. The page scan during
> COPY FREEZE is necessary and it's very cheaper than doing in the first
> vacuum.

I have removed Ibrar as a reviewer since there has been no review from 
them in three weeks, and too encourage others to have a look.

Regards,
-- 
-David
david@pgmasters.net