Horton

Re: should frontend tools use syncfs() ?

Justin Pryzby <pryzby@telsasoft.com>

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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
Date: 2023-09-01T17:58:10Z
Lists: pgsql-hackers 
> +	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 +++

Commits

  1. Adjust documentation for syncfs().

  2. Improve the naming in wal_sync_method code.

  3. Allow using syncfs() in frontend utilities.

  4. Add support for syncfs() in frontend support functions.

  5. Make enum for sync methods available to frontend code.

  6. Move PG_TEMP_FILE* macros to file_utils.h.

  7. Change client-side fsync_fname() to report errors fatally