Message-ID: <e2549085-5246-4edc-bc62-ae19df48acc5@oss.nttdata.com>
Date: Thu, 11 Jul 2024 19:51:20 +0900
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Subject: Re: Add a GUC check hook to ensure summarize_wal cannot be enabled
 when wal_level is minimal
To: Robert Haas <robertmhaas@gmail.com>
Cc: Nathan Bossart <nathandbossart@gmail.com>,
 pgsql-hackers@lists.postgresql.org
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From: Fujii Masao <masao.fujii@oss.nttdata.com>
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On 2024/07/11 1:35, Robert Haas wrote:
> On Wed, Jul 10, 2024 at 10:10 AM Robert Haas <robertmhaas@gmail.com> wrote:
>> On Wed, Jul 10, 2024 at 1:56 AM Fujii Masao <masao.fujii@oss.nttdata.com> wrote:
>>> I believe this issue occurs when the server is shut down cleanly.
>>> The shutdown-checkpoint record retains the wal_level value used
>>> before the shutdown. If wal_level is changed after this,
>>> the wal_level that indicated by the shutdown-checkpoint record
>>> and that the WAL data generated afterwards depends on may not match.
>>
>> Oh, that's a problem. I'll have to think about that.
> 
> Here is an attempt at fixing this problem.

Thanks for updating the patch!

+	 * fast_forward is normally false, but is true when we have encountered
+	 * WAL generated with wal_level=minimal and are skipping over it without
+	 * emitting summary files. In this case, summarized_tli and summarized_lsn
+	 * will advance even though nothing is being written to disk, until we
+	 * again reach a point where wal_level>minimal.
+	 *
  	 * summarizer_pgprocno is the proc number of the summarizer process, if
  	 * one is running, or else INVALID_PROC_NUMBER.
  	 *
@@ -83,6 +89,7 @@ typedef struct
  	TimeLineID	summarized_tli;
  	XLogRecPtr	summarized_lsn;
  	bool		lsn_is_exact;
+	bool		fast_forward;

It looks like the fast_forward field in WalSummarizerData is no longer necessary.

So far, I haven't found any other issues with the patch.

Regards,

-- 
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION