Add support for zstd base backup compression.

Both client-side compression and server-side compression are now
supported for zstd. In addition, a backup compressed by the server
using zstd can now be decompressed by the client in order to
accommodate the use of -Fp.

Jeevan Ladhe, with some edits by me.

Discussion: http://postgr.es/m/CA+Tgmobyzfbz=gyze2_LL1ZumZunmaEKbHQxjrFkOR7APZGu-g@mail.gmail.com

Author: robertmhaas

doc/src/sgml/protocol.sgml

@@ -2724,8 +2724,8 @@ The commands accepted in replication mode are:
         <listitem>
          <para>
           Instructs the server to compress the backup using the specified
-          method. Currently, the supported methods are <literal>gzip</literal>
-          and <literal>lz4</literal>.
+          method. Currently, the supported methods are <literal>gzip</literal>,
+          <literal>lz4</literal>, and <literal>zstd</literal>.
          </para>
         </listitem>
        </varlistentry>
@@ -2737,7 +2737,8 @@ The commands accepted in replication mode are:
           Specifies the compression level to be used. This should only be
           used in conjunction with the <literal>COMPRESSION</literal> option.
           For <literal>gzip</literal> the value should be an integer between 1
-          and 9, and for <literal>lz4</literal> it should be between 1 and 12.
+          and 9, for <literal>lz4</literal> between 1 and 12, and for
+          <literal>zstd</literal> it should be between 1 and 22.
          </para>
         </listitem>
        </varlistentry>

doc/src/sgml/ref/pg_basebackup.sgml

@@ -417,30 +417,33 @@ PostgreSQL documentation
         specify <literal>-Xfetch</literal>.
        </para>
        <para>
-        The compression method can be set to <literal>gzip</literal> or
-        <literal>lz4</literal>, or <literal>none</literal> for no
-        compression. A compression level can be optionally specified, by
-        appending the level number after a colon (<literal>:</literal>). If no
-        level is specified, the default compression level will be used. If
-        only a level is specified without mentioning an algorithm,
-        <literal>gzip</literal> compression will be used if the level is
-        greater than 0, and no compression will be used if the level is 0.
-       </para>
-       <para>
-        When the tar format is used with <literal>gzip</literal> or
-        <literal>lz4</literal>, the suffix <filename>.gz</filename> or
-        <filename>.lz4</filename> will automatically be added to all tar
-        filenames. When the plain format is used, client-side compression may
-        not be specified, but it is still possible to request server-side
-        compression. If this is done, the server will compress the backup for
-        transmission, and the client will decompress and extract it.
+        The compression method can be set to <literal>gzip</literal>,
+        <literal>lz4</literal>, <literal>zstd</literal>, or
+        <literal>none</literal> for no compression. A compression level can
+        optionally be specified, by appending the level number after a colon
+        (<literal>:</literal>). If no level is specified, the default
+        compression level will be used. If only a level is specified without
+        mentioning an algorithm, <literal>gzip</literal> compression will be
+        used if the level is greater than 0, and no compression will be used if
+        the level is 0.
+       </para>
+       <para>
+        When the tar format is used with <literal>gzip</literal>,
+        <literal>lz4</literal>, or <literal>zstd</literal>, the suffix
+        <filename>.gz</filename>, <filename>.lz4</filename>, or
+        <filename>.zst</filename>, respectively, will be automatically added to
+        all tar filenames. When the plain format is used, client-side
+        compression may not be specified, but it is still possible to request
+        server-side compression. If this is done, the server will compress the
+        backup for transmission, and the client will decompress and extract it.
        </para>
        <para>
         When this option is used in combination with
         <literal>-Xstream</literal>, <literal>pg_wal.tar</literal> will
         be compressed using <literal>gzip</literal> if client-side gzip
-        compression is selected, but will not be compressed if server-side
-        compresion or LZ4 compresion is selected.
+        compression is selected, but will not be compressed if any other
+        compression algorithm is selected, or if server-side compression
+        is selected.
        </para>
       </listitem>
      </varlistentry>

src/backend/replication/Makefile

@@ -20,6 +20,7 @@ OBJS = \
 	basebackup_copy.o \
 	basebackup_gzip.o \
 	basebackup_lz4.o \
+	basebackup_zstd.o \
 	basebackup_progress.o \
 	basebackup_server.o \
 	basebackup_sink.o \

src/backend/replication/basebackup.c

@@ -64,7 +64,8 @@ typedef enum
 {
 	BACKUP_COMPRESSION_NONE,
 	BACKUP_COMPRESSION_GZIP,
-	BACKUP_COMPRESSION_LZ4
+	BACKUP_COMPRESSION_LZ4,
+	BACKUP_COMPRESSION_ZSTD
 } basebackup_compression_type;
 
 typedef struct
@@ -906,6 +907,8 @@ parse_basebackup_options(List *options, basebackup_options *opt)
 				opt->compression = BACKUP_COMPRESSION_GZIP;
 			else if (strcmp(optval, "lz4") == 0)
 				opt->compression = BACKUP_COMPRESSION_LZ4;
+			else if (strcmp(optval, "zstd") == 0)
+				opt->compression = BACKUP_COMPRESSION_ZSTD;
 			else
 				ereport(ERROR,
 						(errcode(ERRCODE_SYNTAX_ERROR),
@@ -1026,6 +1029,8 @@ SendBaseBackup(BaseBackupCmd *cmd)
 		sink = bbsink_gzip_new(sink, opt.compression_level);
 	else if (opt.compression == BACKUP_COMPRESSION_LZ4)
 		sink = bbsink_lz4_new(sink, opt.compression_level);
+	else if (opt.compression == BACKUP_COMPRESSION_ZSTD)
+		sink = bbsink_zstd_new(sink, opt.compression_level);
 
 	/* Set up progress reporting. */
 	sink = bbsink_progress_new(sink, opt.progress);