initdb: Add --no-sync-data-files.

This new option instructs initdb to skip synchronizing any files
in database directories, the database directories themselves, and
the tablespace directories, i.e., everything in the base/
subdirectory and any other tablespace directories.  Other files,
such as those in pg_wal/ and pg_xact/, will still be synchronized
unless --no-sync is also specified.  --no-sync-data-files is
primarily intended for internal use by tools that separately ensure
the skipped files are synchronized to disk.  A follow-up commit
will use this to help optimize pg_upgrade's file transfer step.

The --sync-method=fsync implementation of this option makes use of
a new exclude_dir parameter for walkdir().  When not NULL,
exclude_dir specifies a directory to skip processing.  The
--sync-method=syncfs implementation of this option just skips
synchronizing the non-default tablespace directories.  This means
that initdb will still synchronize some or all of the database
files, but there's not much we can do about that.

Discussion: https://postgr.es/m/Zyvop-LxLXBLrZil%40nathan

1 files changed, 27 insertions, 0 deletions

diff --git a/doc/src/sgml/ref/initdb.sgml b/doc/src/sgml/ref/initdb.sgml
index 0026318485a..2f1f9a42f90 100644
--- a/doc/src/sgml/ref/initdb.sgml
+++ b/doc/src/sgml/ref/initdb.sgml
@@ -527,6 +527,33 @@ PostgreSQL documentation
       </listitem>
      </varlistentry>
 
+     <varlistentry id="app-initdb-option-no-sync-data-files">
+      <term><option>--no-sync-data-files</option></term>
+      <listitem>
+       <para>
+        By default, <command>initdb</command> safely writes all database files
+        to disk.  This option instructs <command>initdb</command> to skip
+        synchronizing all files in the individual database directories, the
+        database directories themselves, and the tablespace directories, i.e.,
+        everything in the <filename>base</filename> subdirectory and any other
+        tablespace directories.  Other files, such as those in
+        <literal>pg_wal</literal> and <literal>pg_xact</literal>, will still be
+        synchronized unless the <option>--no-sync</option> option is also
+        specified.
+       </para>
+       <para>
+        Note that if <option>--no-sync-data-files</option> is used in
+        conjuction with <option>--sync-method=syncfs</option>, some or all of
+        the aforementioned files and directories will be synchronized because
+        <literal>syncfs</literal> processes entire file systems.
+       </para>
+       <para>
+        This option is primarily intended for internal use by tools that
+        separately ensure the skipped files are synchronized to disk.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry id="app-initdb-option-no-instructions">
       <term><option>--no-instructions</option></term>
       <listitem>