Date: Thu, 14 Mar 2024 16:00:10 -0500
From: Nathan Bossart <nathandbossart@gmail.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Matthias van de Meent <boekewurm+postgres@gmail.com>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: cleanup patches for incremental backup
Message-ID: <20240314210010.GA3056455@nathanxps13>
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On Wed, Jan 24, 2024 at 12:05:15PM -0600, Nathan Bossart wrote:
> There might be an overflow risk in the cutoff time calculation, but I doubt
> that's the root cause of these failures:
> 
> 	/*
> 	 * Files should only be removed if the last modification time precedes the
> 	 * cutoff time we compute here.
> 	 */
> 	cutoff_time = time(NULL) - 60 * wal_summary_keep_time;

I've attached a short patch for fixing this overflow risk.  Specifically,
it limits wal_summary_keep_time to INT_MAX / SECS_PER_MINUTE, just like
log_rotation_age.

I considering checking for overflow when we subtract the keep-time from the
result of time(2), but AFAICT there's only a problem if time_t is unsigned,
which Wikipedia leads me to believe is unusual [0], so I figured we might
be able to just wait this one out until 2038.

> Otherwise, I think we'll probably need to add some additional logging to
> figure out what is happening...

Separately, I suppose it's probably time to revert the temporary debugging
code adding by commit 5ddf997.  I can craft a patch for that, too.

[0] https://en.wikipedia.org/wiki/Unix_time#Representing_the_number

-- 
Nathan Bossart
Amazon Web Services: https://aws.amazon.com

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diff --git a/src/backend/postmaster/walsummarizer.c b/src/backend/postmaster/walsummarizer.c
index ec2874c18c..c820d1f9ed 100644
--- a/src/backend/postmaster/walsummarizer.c
+++ b/src/backend/postmaster/walsummarizer.c
@@ -139,7 +139,7 @@ static XLogRecPtr redo_pointer_at_last_summary_removal = InvalidXLogRecPtr;
  * GUC parameters
  */
 bool		summarize_wal = false;
-int			wal_summary_keep_time = 10 * 24 * 60;
+int			wal_summary_keep_time = 10 * HOURS_PER_DAY * MINS_PER_HOUR;
 
 static void WalSummarizerShutdown(int code, Datum arg);
 static XLogRecPtr GetLatestLSN(TimeLineID *tli);
@@ -1474,7 +1474,7 @@ MaybeRemoveOldWalSummaries(void)
 	 * Files should only be removed if the last modification time precedes the
 	 * cutoff time we compute here.
 	 */
-	cutoff_time = time(NULL) - 60 * wal_summary_keep_time;
+	cutoff_time = time(NULL) - wal_summary_keep_time * SECS_PER_MINUTE;
 
 	/* Get all the summaries that currently exist. */
 	wslist = GetWalSummaries(0, InvalidXLogRecPtr, InvalidXLogRecPtr);
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index 57d9de4dd9..1e71e7db4a 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -3293,9 +3293,9 @@ struct config_int ConfigureNamesInt[] =
 			GUC_UNIT_MIN,
 		},
 		&wal_summary_keep_time,
-		10 * 24 * 60,			/* 10 days */
+		10 * HOURS_PER_DAY * MINS_PER_HOUR, /* 10 days */
 		0,
-		INT_MAX,
+		INT_MAX / SECS_PER_MINUTE,
 		NULL, NULL, NULL
 	},
 

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