Allow parallel zstd compression when taking a base backup.

libzstd allows transparent parallel compression just by setting
an option when creating the compression context, so permit that
for both client and server-side backup compression. To use this,
use something like pg_basebackup --compress WHERE-zstd:workers=N
where WHERE is "client" or "server" and N is an integer.

When compression is performed on the server side, this will spawn
threads inside the PostgreSQL backend. While there is almost no
PostgreSQL server code which is thread-safe, the threads here are used
internally by libzstd and touch only data structures controlled by
libzstd.

Patch by me, based in part on earlier work by Dipesh Pandit
and Jeevan Ladhe. Reviewed by Justin Pryzby.

Discussion: http://postgr.es/m/CA+Tgmobj6u-nWF-j=FemygUhobhryLxf9h-wJN7W-2rSsseHNA@mail.gmail.com

src/backend/replication/basebackup_zstd.c

@@ -25,8 +25,8 @@ typedef struct bbsink_zstd
 	/* Common information for all types of sink. */
 	bbsink		base;
 
-	/* Compression level */
-	int			compresslevel;
+	/* Compression options */
+	bc_specification *compress;
 
 	ZSTD_CCtx  *cctx;
 	ZSTD_outBuffer zstd_outBuf;
@@ -67,22 +67,13 @@ bbsink_zstd_new(bbsink *next, bc_specification *compress)
 	return NULL;				/* keep compiler quiet */
 #else
 	bbsink_zstd *sink;
-	int		compresslevel;
 
 	Assert(next != NULL);
 
-	if ((compress->options & BACKUP_COMPRESSION_OPTION_LEVEL) == 0)
-		compresslevel = 0;
-	else
-	{
-		compresslevel = compress->level;
-		Assert(compresslevel >= 1 && compresslevel <= 22);
-	}
-
 	sink = palloc0(sizeof(bbsink_zstd));
 	*((const bbsink_ops **) &sink->base.bbs_ops) = &bbsink_zstd_ops;
 	sink->base.bbs_next = next;
-	sink->compresslevel = compresslevel;
+	sink->compress = compress;
 
 	return &sink->base;
 #endif
@@ -99,16 +90,36 @@ bbsink_zstd_begin_backup(bbsink *sink)
 	bbsink_zstd *mysink = (bbsink_zstd *) sink;
 	size_t		output_buffer_bound;
 	size_t		ret;
+	bc_specification *compress = mysink->compress;
 
 	mysink->cctx = ZSTD_createCCtx();
 	if (!mysink->cctx)
 		elog(ERROR, "could not create zstd compression context");
 
-	ret = ZSTD_CCtx_setParameter(mysink->cctx, ZSTD_c_compressionLevel,
-								 mysink->compresslevel);
-	if (ZSTD_isError(ret))
-		elog(ERROR, "could not set zstd compression level to %d: %s",
-			 mysink->compresslevel, ZSTD_getErrorName(ret));
+	if ((compress->options & BACKUP_COMPRESSION_OPTION_LEVEL) != 0)
+	{
+		ret = ZSTD_CCtx_setParameter(mysink->cctx, ZSTD_c_compressionLevel,
+									 compress->level);
+		if (ZSTD_isError(ret))
+			elog(ERROR, "could not set zstd compression level to %d: %s",
+				 compress->level, ZSTD_getErrorName(ret));
+	}
+
+	if ((compress->options & BACKUP_COMPRESSION_OPTION_WORKERS) != 0)
+	{
+		/*
+		 * On older versions of libzstd, this option does not exist, and trying
+		 * to set it will fail. Similarly for newer versions if they are
+		 * compiled without threading support.
+		 */
+		ret = ZSTD_CCtx_setParameter(mysink->cctx, ZSTD_c_nbWorkers,
+									 compress->workers);
+		if (ZSTD_isError(ret))
+			ereport(ERROR,
+					errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+					errmsg("could not set compression worker count to %d: %s",
+						   compress->workers, ZSTD_getErrorName(ret)));
+	}
 
 	/*
 	 * We need our own buffer, because we're going to pass different data to

src/bin/pg_basebackup/bbstreamer_zstd.c

@@ -67,7 +67,6 @@ bbstreamer_zstd_compressor_new(bbstreamer *next, bc_specification *compress)
 {
 #ifdef USE_ZSTD
 	bbstreamer_zstd_frame *streamer;
-	int			compresslevel;
 	size_t		ret;
 
 	Assert(next != NULL);
@@ -88,18 +87,35 @@ bbstreamer_zstd_compressor_new(bbstreamer *next, bc_specification *compress)
 		exit(1);
 	}
 
-	/* Initialize stream compression preferences */
-	if ((compress->options & BACKUP_COMPRESSION_OPTION_LEVEL) == 0)
-		compresslevel = 0;
-	else
-		compresslevel = compress->level;
-	ret = ZSTD_CCtx_setParameter(streamer->cctx, ZSTD_c_compressionLevel,
-								 compresslevel);
-	if (ZSTD_isError(ret))
+	/* Set compression level, if specified */
+	if ((compress->options & BACKUP_COMPRESSION_OPTION_LEVEL) != 0)
 	{
-		pg_log_error("could not set zstd compression level to %d: %s",
-					 compresslevel, ZSTD_getErrorName(ret));
-		exit(1);
+		ret = ZSTD_CCtx_setParameter(streamer->cctx, ZSTD_c_compressionLevel,
+									 compress->level);
+		if (ZSTD_isError(ret))
+		{
+			pg_log_error("could not set zstd compression level to %d: %s",
+						 compress->level, ZSTD_getErrorName(ret));
+			exit(1);
+		}
+	}
+
+	/* Set # of workers, if specified */
+	if ((compress->options & BACKUP_COMPRESSION_OPTION_WORKERS) != 0)
+	{
+		/*
+		 * On older versions of libzstd, this option does not exist, and
+		 * trying to set it will fail. Similarly for newer versions if they
+		 * are compiled without threading support.
+		 */
+		ret = ZSTD_CCtx_setParameter(streamer->cctx, ZSTD_c_nbWorkers,
+									 compress->workers);
+		if (ZSTD_isError(ret))
+		{
+			pg_log_error("could not set compression worker count to %d: %s",
+						 compress->workers, ZSTD_getErrorName(ret));
+			exit(1);
+		}
 	}
 
 	/* Initialize the ZSTD output buffer. */

src/bin/pg_basebackup/t/010_pg_basebackup.pl

@@ -130,6 +130,11 @@ my @compression_failure_tests = (
 		'invalid compression specification: found empty string where a compression option was expected',
 		'failure on extra, empty compression option'
 	],
+	[
+		'gzip:workers=3',
+		'invalid compression specification: compression algorithm "gzip" does not accept a worker count',
+		'failure on worker count for gzip'
+	],
 );
 for my $cft (@compression_failure_tests)
 {

src/bin/pg_verifybackup/t/009_extract.pl

@@ -34,6 +34,12 @@ my @test_configuration = (
 		'compression_method' => 'zstd',
 		'backup_flags' => ['--compress', 'server-zstd:5'],
 		'enabled' => check_pg_config("#define USE_ZSTD 1")
+	},
+	{
+		'compression_method' => 'parallel zstd',
+		'backup_flags' => ['--compress', 'server-zstd:workers=3'],
+		'enabled' => check_pg_config("#define USE_ZSTD 1"),
+		'possibly_unsupported' => qr/could not set compression worker count to 3: Unsupported parameter/
 	}
 );
 
@@ -55,8 +61,27 @@ for my $tc (@test_configuration)
 		my @verify = ('pg_verifybackup', '-e', $backup_path);
 
 		# A backup with a valid compression method should work.
-		$primary->command_ok(\@backup,
-							 "backup done, compression method \"$method\"");
+		my $backup_stdout = '';
+		my $backup_stderr = '';
+		my $backup_result = $primary->run_log(\@backup, '>', \$backup_stdout,
+											  '2>', \$backup_stderr);
+		if ($backup_stdout ne '')
+		{
+			print "# standard output was:\n$backup_stdout";
+		}
+		if ($backup_stderr ne '')
+		{
+			print "# standard error was:\n$backup_stderr";
+		}
+		if (! $backup_result && $tc->{'possibly_unsupported'} &&
+			$backup_stderr =~ /$tc->{'possibly_unsupported'}/)
+		{
+			skip "compression with $method not supported by this build", 2;
+		}
+		else
+		{
+			ok($backup_result, "backup done, compression $method");
+		}
 
 		# Make sure that it verifies OK.
 		$primary->command_ok(\@verify,

src/bin/pg_verifybackup/t/010_client_untar.pl

@@ -49,6 +49,15 @@ my @test_configuration = (
 		'decompress_program' => $ENV{'ZSTD'},
 		'decompress_flags' => [ '-d' ],
 		'enabled' => check_pg_config("#define USE_ZSTD 1")
+	},
+	{
+		'compression_method' => 'parallel zstd',
+		'backup_flags' => ['--compress', 'client-zstd:workers=3'],
+		'backup_archive' => 'base.tar.zst',
+		'decompress_program' => $ENV{'ZSTD'},
+		'decompress_flags' => [ '-d' ],
+		'enabled' => check_pg_config("#define USE_ZSTD 1"),
+		'possibly_unsupported' => qr/could not set compression worker count to 3: Unsupported parameter/
 	}
 );
 
@@ -69,9 +78,27 @@ for my $tc (@test_configuration)
 			'pg_basebackup', '-D', $backup_path,
 			'-Xfetch', '--no-sync', '-cfast', '-Ft');
 		push @backup, @{$tc->{'backup_flags'}};
-		$primary->command_ok(\@backup,
-							 "client side backup, compression $method");
-
+		my $backup_stdout = '';
+		my $backup_stderr = '';
+		my $backup_result = $primary->run_log(\@backup, '>', \$backup_stdout,
+											  '2>', \$backup_stderr);
+		if ($backup_stdout ne '')
+		{
+			print "# standard output was:\n$backup_stdout";
+		}
+		if ($backup_stderr ne '')
+		{
+			print "# standard error was:\n$backup_stderr";
+		}
+		if (! $backup_result && $tc->{'possibly_unsupported'} &&
+			$backup_stderr =~ /$tc->{'possibly_unsupported'}/)
+		{
+			skip "compression with $method not supported by this build", 3;
+		}
+		else
+		{
+			ok($backup_result, "client side backup, compression $method");
+		}
 
 		# Verify that the we got the files we expected.
 		my $backup_files = join(',',

src/common/backup_compression.c

@@ -177,6 +177,11 @@ parse_bc_specification(bc_algorithm algorithm, char *specification,
 			result->level = expect_integer_value(keyword, value, result);
 			result->options |= BACKUP_COMPRESSION_OPTION_LEVEL;
 		}
+		else if (strcmp(keyword, "workers") == 0)
+		{
+			result->workers = expect_integer_value(keyword, value, result);
+			result->options |= BACKUP_COMPRESSION_OPTION_WORKERS;
+		}
 		else
 			result->parse_error =
 				psprintf(_("unknown compression option \"%s\""), keyword);
@@ -266,5 +271,16 @@ validate_bc_specification(bc_specification *spec)
 							min_level, max_level);
 	}
 
+	/*
+	 * Of the compression algorithms that we currently support, only zstd
+	 * allows parallel workers.
+	 */
+	if ((spec->options & BACKUP_COMPRESSION_OPTION_WORKERS) != 0 &&
+		(spec->algorithm != BACKUP_COMPRESSION_ZSTD))
+	{
+		return psprintf(_("compression algorithm \"%s\" does not accept a worker count"),
+						get_bc_algorithm_name(spec->algorithm));
+	}
+
 	return NULL;
 }

src/include/common/backup_compression.h

@@ -23,12 +23,14 @@ typedef enum bc_algorithm
 } bc_algorithm;
 
 #define	BACKUP_COMPRESSION_OPTION_LEVEL			(1 << 0)
+#define BACKUP_COMPRESSION_OPTION_WORKERS		(1 << 1)
 
 typedef struct bc_specification
 {
 	bc_algorithm algorithm;
 	unsigned	options;		/* OR of BACKUP_COMPRESSION_OPTION constants */
 	int			level;
+	int			workers;
 	char	   *parse_error;	/* NULL if parsing was OK, else message */
 } bc_specification;