Date: Fri, 1 Sep 2023 12:58:10 -0500
From: Justin Pryzby <pryzby@telsasoft.com>
To: Nathan Bossart <nathandbossart@gmail.com>
Cc: Michael Paquier <michael@paquier.xyz>,
	Thomas Munro <thomas.munro@gmail.com>,
	David Steele <david@pgmasters.net>,
	Fujii Masao <masao.fujii@oss.nttdata.com>,
	Bruce Momjian <bruce@momjian.us>, Paul Guo <guopa@vmware.com>,
	Tom Lane <tgl@sss.pgh.pa.us>,
	Michael Brown <michael.brown@discourse.org>,
	pgsql-hackers@postgresql.org
Subject: Re: should frontend tools use syncfs() ?
Message-ID: <ZPImMi8smaPsXjGK@pryzbyj2023>
References: <20210930004340.GM831@telsasoft.com>
 <YVUz0Ay9KshniWBe@paquier.xyz>
 <20220413115412.GM26620@telsasoft.com>
 <20230729214010.GA189456@nathanxps13>
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> +	if (!user_opts.sync_method)
> +		user_opts.sync_method = pg_strdup("fsync");

why pstrdup?

> +parse_sync_method(const char *optarg, SyncMethod *sync_method)
> +{
> +	if (strcmp(optarg, "fsync") == 0)
> +		*sync_method = SYNC_METHOD_FSYNC;
> +#ifdef HAVE_SYNCFS
> +	else if (strcmp(optarg, "syncfs") == 0)
> +		*sync_method = SYNC_METHOD_SYNCFS;
> +#endif
> +	else
> +	{
> +		pg_log_error("unrecognized sync method: %s", optarg);
> +		return false;
> +	}

This should probably give a distinct error when syncfs is not supported
than when it's truely recognized.

The patch should handle pg_dumpall, too.

Note that /bin/sync doesn't try to de-duplicate, it does just what you
tell it.

$ strace -e openat,syncfs,fsync sync / / / -f
...
openat(AT_FDCWD, "/", O_RDONLY|O_NONBLOCK) = 3
syncfs(3)                               = 0
openat(AT_FDCWD, "/", O_RDONLY|O_NONBLOCK) = 3
syncfs(3)                               = 0
openat(AT_FDCWD, "/", O_RDONLY|O_NONBLOCK) = 3
syncfs(3)                               = 0
+++ exited with 0 +++