Re: Adding a TAP test checking data consistency on standby with minRecoveryPoint

From: Michael Paquier <michael(at)paquier(dot)xyz>
To: Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk>
Cc: Postgres hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Adding a TAP test checking data consistency on standby with minRecoveryPoint
Date: 2018-11-12 04:08:38
Message-ID: 20181112040838.GA2631@paquier.xyz
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On Fri, Nov 09, 2018 at 12:42:27PM +0000, Andrew Gierth wrote:
> Seems simple enough - the LSN on the page is actually two 4-byte values
> with the most significant one first, regardless of platform byte order
> (though each individual word is in native order), so
>
> my ($hi,$lo) = unpack("LL", $buf);
>
> should suffice. ("L" is always 32 bits regardless of platform, and it
> has the platform's endianness.)

Thanks for the review, Andrew. And I completely forgot that this is at
the beginning of the page.

> Looking only at the last page seems questionable.

I have switched also the online check so as it also looks at the full
range of blocks instead of only the last one.

> Something like this should work to return the largest LSN of any page
> in the specified list of files:
>
> # find_largest_lsn(blocksize,filenames...)
> sub find_largest_lsn

Thanks! I am stealing that stuff, and I have added an offline check by
comparing the value of minRecoveryPoint in pg_controldata. Again, if
you revert c186ba13 and run the tests, both online and offline failures
are showing up.

What do you think?
--
Michael

Attachment Content-Type Size
recovery-min-lsn-tap-v2.patch text/x-diff 7.5 KB

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