Rework compression options of pg_receivewal

Since babbbb5 and the introduction of LZ4 in pg_receivewal, the
compression of the WAL archived is controlled by two options:
- --compression-method with "gzip", "none" or "lz4" as possible value.
- --compress=N to specify a compression level.  This includes a
backward-incompatible change where a value of 0 leads to a failure
instead of no compression enforced.

This commit takes advantage of a4b5754 and 3603f7c to rework the
compression options of pg_receivewal, as of:
- The removal of --compression-method.
- The extenction of --compress to use the same grammar as pg_basebackup,
with a METHOD:DETAIL format, where a METHOD is "gzip", "none" or "lz4"
and a DETAIL is a comma-separated list of options, the only keyword
supported is now "level" to control the compression level.  If only an
integer is specified as value of this option, "none" is implied on 0
and "gzip" is implied otherwise.  This brings back --compress to be
backward-compatible with ~14, while still supporting LZ4.

This has also the advantage of centralizing the set of checks used by
pg_receivewal to validate its compression options.

Author: Michael Paquier
Reviewed-by: Robert Haas, Georgios Kokolatos
Discussion: https://postgr.es/m/YlPQGNAAa04raObK@paquier.xyz

1 files changed, 22 insertions, 23 deletions

diff --git a/doc/src/sgml/ref/pg_receivewal.sgml b/doc/src/sgml/ref/pg_receivewal.sgml
index b846213fb7b..4fe9e1a8742 100644
--- a/doc/src/sgml/ref/pg_receivewal.sgml
+++ b/doc/src/sgml/ref/pg_receivewal.sgml
@@ -263,37 +263,36 @@ PostgreSQL documentation
      </varlistentry>
 
      <varlistentry>
-      <term><option>--compression-method=<replaceable class="parameter">method</replaceable></option></term>
+      <term><option>-Z <replaceable class="parameter">level</replaceable></option></term>
+      <term><option>-Z <replaceable class="parameter">method</replaceable>[:<replaceable>detail</replaceable>]</option></term>
+      <term><option>--compress=<replaceable class="parameter">level</replaceable></option></term>
+      <term><option>--compress=<replaceable class="parameter">method</replaceable>[:<replaceable>detail</replaceable>]</option></term>
       <listitem>
        <para>
-        Enables compression of write-ahead logs using the specified method.
-        Supported values are <literal>gzip</literal>, <literal>lz4</literal>
-        (if <productname>PostgreSQL</productname> was compiled with
-        <option>--with-lz4</option>), and <literal>none</literal>.
+        Enables compression of write-ahead logs.
        </para>
-
        <para>
-        The suffix <filename>.gz</filename> will automatically be added to
-        all filenames when using <literal>gzip</literal>, and the suffix
-        <filename>.lz4</filename> is added when using <literal>lz4</literal>.
+        The compression method can be set to <literal>gzip</literal>,
+        <literal>lz4</literal> (if <productname>PostgreSQL</productname>
+        was compiled with <option>--with-lz4</option>) or
+        <literal>none</literal> for no compression.
+        A compression detail string can optionally be specified.  If the
+        detail string is an integer, it specifies the compression level.
+        Otherwise, it should be a comma-separated list of items, each of the
+        form <literal>keyword</literal> or <literal>keyword=value</literal>.
+        Currently, the only supported keyword is <literal>level</literal>.
        </para>
-      </listitem>
-     </varlistentry>
-
-     <varlistentry>
-      <term><option>-Z <replaceable class="parameter">level</replaceable></option></term>
-      <term><option>--compress=<replaceable class="parameter">level</replaceable></option></term>
-      <listitem>
        <para>
-        Specifies the compression level (<literal>1</literal> through
-        <literal>9</literal>, <literal>1</literal> being worst compression
-        and <literal>9</literal> being best compression) for WAL segments
-        compressed with <application>gzip</application>.
+        If no compression 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>
-        This option requires <option>--compression-method</option> to be
-        specified with <literal>gzip</literal>.
+        The suffix <filename>.gz</filename> will automatically be added to
+        all filenames when using <literal>gzip</literal>, and the suffix
+        <filename>.lz4</filename> is added when using <literal>lz4</literal>.
        </para>
       </listitem>
      </varlistentry>