Re: [HACKERS] Should buffer of initialization fork have aBM_PERMANENT flag

On Wed, Jan 25, 2017 at 7:14 PM, Michael Paquier
<michael.paquier@gmail.com> wrote:
> (Adding Robert in CC.)
>
> On Thu, Jan 26, 2017 at 4:34 AM, Wang Hao <whberet@gmail.com> wrote:
>> An unlogged table has an initialization fork. The initialization fork does
>> not have an BM_PERMANENT flag when get a buffer.
>> In checkpoint (not shutdown or end of recovery), it will not write to disk.
>> after a crash recovery, the page of initialization fork will not correctly,
>> then make the main fork not correctly too.
>
> For init forks the flush need absolutely to happen, so that's really
> not good. We ought to fix BufferAlloc() appropriately here.

I agree with that, but I propose the attached version instead.  It
seems cleaner to have the entire test for setting BM_PERMANENT in one
place rather than splitting it up as you did.

I believe this sets a record for the longest-lived data corruption bug
in a commit made by me.  Six years and change, woohoo.  :-(

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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