From d2eb46fb18258931f65e2b01ac6b406255f3c575 Mon Sep 17 00:00:00 2001
From: Nazir Bilal Yavuz <byavuz81@gmail.com>
Date: Thu, 8 Aug 2024 15:01:48 +0300
Subject: [PATCH v10] Introduce file_copy_method GUC

This GUC can be set to either COPY (default) or CLONE (if system
supports it).

If CLONE method is chosen, similar to COPY; but attempting to use
efficient file copying system calls.  The kernel has the opportunity to
share block ranges in copy-on-write file systems, or maybe push down
the copy to network file systems and storage devices.

Currently works on Linux, FreeBSD and macOS.  More systems could be
supported.

Author: Thomas Munro <thomas.munro@gmail.com>
Author: Nazir Bilal Yavuz <byavuz81@gmail.com>
Reviewed-by: Robert Haas <robertmhaas@gmail.com>
Reviewed-by: Ranier Vilela <ranier.vf@gmail.com>
Discussion: https://postgr.es/m/CA%2BhUKGLM%2Bt%2BSwBU-cHeMUXJCOgBxSHLGZutV5zCwY4qrCcE02w%40mail.gmail.com
---
 src/include/storage/copydir.h                 |  9 ++
 src/backend/storage/file/copydir.c            | 86 ++++++++++++++++++-
 .../utils/activity/wait_event_names.txt       |  1 +
 src/backend/utils/misc/guc_tables.c           | 19 ++++
 src/backend/utils/misc/postgresql.conf.sample |  4 +
 doc/src/sgml/config.sgml                      | 46 ++++++++++
 doc/src/sgml/ref/alter_database.sgml          |  3 +-
 doc/src/sgml/ref/create_database.sgml         |  4 +-
 src/tools/pgindent/typedefs.list              |  1 +
 9 files changed, 170 insertions(+), 3 deletions(-)

diff --git a/src/include/storage/copydir.h b/src/include/storage/copydir.h
index cf60e63f4e2..940d74462d1 100644
--- a/src/include/storage/copydir.h
+++ b/src/include/storage/copydir.h
@@ -13,6 +13,15 @@
 #ifndef COPYDIR_H
 #define COPYDIR_H
 
+typedef enum FileCopyMethod
+{
+	FILE_COPY_METHOD_COPY,
+	FILE_COPY_METHOD_CLONE,
+} FileCopyMethod;
+
+/* GUC parameters */
+extern PGDLLIMPORT int file_copy_method;
+
 extern void copydir(const char *fromdir, const char *todir, bool recurse);
 extern void copy_file(const char *fromfile, const char *tofile);
 
diff --git a/src/backend/storage/file/copydir.c b/src/backend/storage/file/copydir.c
index c335b60a367..0fa529dfd7d 100644
--- a/src/backend/storage/file/copydir.c
+++ b/src/backend/storage/file/copydir.c
@@ -21,17 +21,30 @@
 #include <fcntl.h>
 #include <unistd.h>
 
+#ifdef HAVE_COPYFILE_H
+#include <copyfile.h>
+#endif
+
 #include "common/file_utils.h"
 #include "miscadmin.h"
 #include "pgstat.h"
 #include "storage/copydir.h"
 #include "storage/fd.h"
 
+/* GUCs */
+int			file_copy_method = FILE_COPY_METHOD_COPY;
+
+static void clone_file(const char *fromfile, const char *tofile);
+
 /*
  * copydir: copy a directory
  *
  * If recurse is false, subdirectories are ignored.  Anything that's not
  * a directory or a regular file is ignored.
+ *
+ * This function uses a file_copy_method GUC to determine copy method.
+ * Uses of this function must be documented in the list of places
+ * affected by this GUC.
  */
 void
 copydir(const char *fromdir, const char *todir, bool recurse)
@@ -71,7 +84,12 @@ copydir(const char *fromdir, const char *todir, bool recurse)
 				copydir(fromfile, tofile, true);
 		}
 		else if (xlde_type == PGFILETYPE_REG)
-			copy_file(fromfile, tofile);
+		{
+			if (file_copy_method == FILE_COPY_METHOD_CLONE)
+				clone_file(fromfile, tofile);
+			else
+				copy_file(fromfile, tofile);
+		}
 	}
 	FreeDir(xldir);
 
@@ -214,3 +232,69 @@ copy_file(const char *fromfile, const char *tofile)
 
 	pfree(buffer);
 }
+
+/*
+ * clone one file
+ */
+static void
+clone_file(const char *fromfile, const char *tofile)
+{
+#if defined(HAVE_COPYFILE) && defined(COPYFILE_CLONE_FORCE)
+	if (copyfile(fromfile, tofile, NULL, COPYFILE_CLONE_FORCE) < 0)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not clone file \"%s\" to \"%s\": %m",
+						fromfile, tofile)));
+#elif defined(HAVE_COPY_FILE_RANGE)
+	int			srcfd;
+	int			dstfd;
+	ssize_t		nbytes;
+
+	srcfd = OpenTransientFile(fromfile, O_RDONLY | PG_BINARY);
+	if (srcfd < 0)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not open file \"%s\": %m", fromfile)));
+
+	dstfd = OpenTransientFile(tofile, O_WRONLY | O_CREAT | O_EXCL | PG_BINARY);
+	if (dstfd < 0)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not create file \"%s\": %m", tofile)));
+
+	do
+	{
+		/* If we got a cancel signal during the copy of the file, quit */
+		CHECK_FOR_INTERRUPTS();
+
+		/*
+		 * Don't copy too much at once, so we can check for interrupts from
+		 * time to time if this falls back to a slow copy.
+		 */
+		pgstat_report_wait_start(WAIT_EVENT_COPY_FILE_COPY);
+		nbytes = copy_file_range(srcfd, NULL, dstfd, NULL, 1024 * 1024, 0);
+		if (nbytes < 0 && errno != EINTR)
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not clone file \"%s\" to \"%s\": %m",
+							fromfile, tofile)));
+		pgstat_report_wait_end();
+	}
+	while (nbytes != 0);
+
+	if (CloseTransientFile(dstfd) != 0)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not close file \"%s\": %m", tofile)));
+
+	if (CloseTransientFile(srcfd) != 0)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not close file \"%s\": %m", fromfile)));
+#else
+	/*
+	 * If there is no CLONE support, this function should not be called.
+	 */
+	pg_unreachable();
+#endif
+}
diff --git a/src/backend/utils/activity/wait_event_names.txt b/src/backend/utils/activity/wait_event_names.txt
index 9fa12a555e8..56500905758 100644
--- a/src/backend/utils/activity/wait_event_names.txt
+++ b/src/backend/utils/activity/wait_event_names.txt
@@ -204,6 +204,7 @@ CONTROL_FILE_SYNC	"Waiting for the <filename>pg_control</filename> file to reach
 CONTROL_FILE_SYNC_UPDATE	"Waiting for an update to the <filename>pg_control</filename> file to reach durable storage."
 CONTROL_FILE_WRITE	"Waiting for a write to the <filename>pg_control</filename> file."
 CONTROL_FILE_WRITE_UPDATE	"Waiting for a write to update the <filename>pg_control</filename> file."
+COPY_FILE_COPY	"Waiting for a file copy operation."
 COPY_FILE_READ	"Waiting for a read during a file copy operation."
 COPY_FILE_WRITE	"Waiting for a write during a file copy operation."
 DATA_FILE_EXTEND	"Waiting for a relation data file to be extended."
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index 989825d3a9c..ac7aec7167c 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -76,6 +76,7 @@
 #include "storage/aio.h"
 #include "storage/bufmgr.h"
 #include "storage/bufpage.h"
+#include "storage/copydir.h"
 #include "storage/io_worker.h"
 #include "storage/large_object.h"
 #include "storage/pg_shmem.h"
@@ -479,6 +480,14 @@ static const struct config_enum_entry wal_compression_options[] = {
 	{NULL, 0, false}
 };
 
+static const struct config_enum_entry file_copy_method_options[] = {
+	{"copy", FILE_COPY_METHOD_COPY, false},
+#if defined(HAVE_COPYFILE) && defined(COPYFILE_CLONE_FORCE) || defined(HAVE_COPY_FILE_RANGE)
+	{"clone", FILE_COPY_METHOD_CLONE, false},
+#endif
+	{NULL, 0, false}
+};
+
 /*
  * Options for enum values stored in other modules
  */
@@ -5252,6 +5261,16 @@ struct config_enum ConfigureNamesEnum[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"file_copy_method", PGC_USERSET, RESOURCES_DISK,
+			gettext_noop("Selects the file copy method."),
+			NULL
+		},
+		&file_copy_method,
+		FILE_COPY_METHOD_COPY, file_copy_method_options,
+		NULL, NULL, NULL
+	},
+
 	{
 		{"wal_sync_method", PGC_SIGHUP, WAL_SETTINGS,
 			gettext_noop("Selects the method used for forcing WAL updates to disk."),
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 0b9e3066bde..b16b1b90ae7 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -183,6 +183,10 @@
 #max_notify_queue_pages = 1048576	# limits the number of SLRU pages allocated
 					# for NOTIFY / LISTEN queue
 
+#file_copy_method = copy	# the default is the first option
+					# 	copy
+					# 	clone (if your system supports)
+
 # - Kernel Resources -
 
 #max_files_per_process = 1000		# min 64
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 69fc93dffc4..239350cabab 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -2347,6 +2347,52 @@ include_dir 'conf.d'
       </listitem>
      </varlistentry>
 
+     <varlistentry id="guc_file_copy_method" xreflabel="file_copy_method">
+      <term><varname>file_copy_method</varname> (<type>enum</type>)
+      <indexterm>
+       <primary><varname>file_copy_method</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        Specifies the copy method that will be used while copying files.
+        Possible values are <literal>COPY</literal> (default) and
+        <literal>CLONE</literal> (if your system supports).
+       </para>
+
+       <para>
+       This parameter controls the method of the copying process in:
+       </para>
+       <itemizedlist>
+        <listitem>
+        <para>
+         <literal>FILE_COPY</literal> strategy in <command>CREATE DATABASE ... STRATEGY=FILE_COPY</command>
+        </para>
+        </listitem>
+        <listitem>
+        <para>
+         <command> ALTER DATABASE ... SET TABLESPACE ... </command>
+        </para>
+        </listitem>
+       </itemizedlist>
+
+       <para>
+        The <literal>CLONE</literal> method works the same way as
+        <literal>COPY</literal> method, except that it uses efficient file
+        cloning (also known as <quote>reflinks</quote> on
+        some systems) instead of copying files to the new data directory,
+        which can result in near-instantaneous copying of the data files.
+       </para>
+
+       <para>
+        File cloning is only supported on some operating systems and file
+        systems.  At present, it is supported on Linux (kernel 4.5 or
+        later) with Btrfs and XFS (on file systems created with reflink
+        support), and on macOS with APFS.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry id="guc-max-notify-queue-pages" xreflabel="max_notify_queue_pages">
       <term><varname>max_notify_queue_pages</varname> (<type>integer</type>)
       <indexterm>
diff --git a/doc/src/sgml/ref/alter_database.sgml b/doc/src/sgml/ref/alter_database.sgml
index 2479c41e8d6..9d8ec677555 100644
--- a/doc/src/sgml/ref/alter_database.sgml
+++ b/doc/src/sgml/ref/alter_database.sgml
@@ -82,7 +82,8 @@ ALTER DATABASE <replaceable class="parameter">name</replaceable> RESET ALL
    default tablespace to the new tablespace.  The new default tablespace
    must be empty for this database, and no one can be connected to
    the database.  Tables and indexes in non-default tablespaces are
-   unaffected.
+   unaffected.  The copy method used while moving could be changed by
+   <xref linkend="guc_file_copy_method"/> option.
   </para>
 
   <para>
diff --git a/doc/src/sgml/ref/create_database.sgml b/doc/src/sgml/ref/create_database.sgml
index a4b052ba08b..70092d2685e 100644
--- a/doc/src/sgml/ref/create_database.sgml
+++ b/doc/src/sgml/ref/create_database.sgml
@@ -138,7 +138,9 @@ CREATE DATABASE <replaceable class="parameter">name</replaceable>
         log volume substantially, especially if the template database is large,
         it also forces the system to perform a checkpoint both before and
         after the creation of the new database. In some situations, this may
-        have a noticeable negative impact on overall system performance.
+        have a noticeable negative impact on overall system performance. The
+        method used in <literal>FILE_COPY</literal> strategy could be changed
+        by <xref linkend="guc_file_copy_method"/> option.
        </para>
       </listitem>
      </varlistentry>
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 3fbf5a4c212..5163f7ee7c5 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -791,6 +791,7 @@ FieldSelect
 FieldStore
 File
 FileBackupMethod
+FileCopyMethod
 FileFdwExecutionState
 FileFdwPlanState
 FileNameMap
-- 
2.47.2

