[PATCH] pg_upgrade: support for btrfs copy-on-write clones

Add file cloning as an alternative data transfer method to pg_upgrade.
Currently only btrfs is supported, but copy-on-write cloning is also
available on at least ZFS. Cloning must be requested explicitly and if
it isn't supported by the operating system or filesystem a fatal error
is thrown.

This provides upgrade performance similar to link mode while allowing
the old cluster to be used even after the new one has been started.

Signed-off-by: Oskari Saarenmaa <os@ohmu.fi>
---
configure | 5 +-
configure.in | 7 ++-
contrib/pg_upgrade/check.c | 3 +
contrib/pg_upgrade/file.c | 125 +++++++++++++++++++++++++++++----------
contrib/pg_upgrade/option.c | 7 +++
contrib/pg_upgrade/pg_upgrade.h | 13 ++--
contrib/pg_upgrade/relfilenode.c | 31 ++++------
doc/src/sgml/pgupgrade.sgml | 7 +++
src/include/pg_config.h.in | 3 +
9 files changed, 141 insertions(+), 60 deletions(-)

diff --git a/configure b/configure
index c685ca3..5087463 100755
--- a/configure
+++ b/configure
@@ -10351,7 +10351,10 @@ done

-for ac_header in crypt.h dld.h fp_class.h getopt.h ieeefp.h ifaddrs.h langinfo.h poll.h pwd.h sys/ioctl.h sys/ipc.h sys/poll.h sys/pstat.h sys/resource.h sys/select.h sys/sem.h sys/shm.h sys/socket.h sys/sockio.h sys/tas.h sys/time.h sys/un.h termios.h ucred.h utime.h wchar.h wctype.h
+for ac_header in crypt.h dld.h fp_class.h getopt.h ieeefp.h ifaddrs.h langinfo.h \
+    linux/btrfs.h poll.h pwd.h sys/ioctl.h sys/ipc.h sys/poll.h sys/pstat.h \
+    sys/resource.h sys/select.h sys/sem.h sys/shm.h sys/socket.h sys/sockio.h \
+    sys/tas.h sys/time.h sys/un.h termios.h ucred.h utime.h wchar.h wctype.h
 do
 as_ac_Header=`$as_echo "ac_cv_header_$ac_header" | $as_tr_sh`
 if { as_var=$as_ac_Header; eval "test \"\${$as_var+set}\" = set"; }; then
diff --git a/configure.in b/configure.in
index 82771bd..609aa73 100644
--- a/configure.in
+++ b/configure.in
@@ -982,7 +982,12 @@ AC_SUBST(OSSP_UUID_LIBS)
 ##

 dnl sys/socket.h is required by AC_FUNC_ACCEPT_ARGTYPES
-AC_CHECK_HEADERS([crypt.h dld.h fp_class.h getopt.h ieeefp.h ifaddrs.h langinfo.h poll.h pwd.h sys/ioctl.h sys/ipc.h sys/poll.h sys/pstat.h sys/resource.h sys/select.h sys/sem.h sys/shm.h sys/socket.h sys/sockio.h sys/tas.h sys/time.h sys/un.h termios.h ucred.h utime.h wchar.h wctype.h])
+AC_CHECK_HEADERS([crypt.h dld.h fp_class.h getopt.h ieeefp.h ifaddrs.h \
+                  langinfo.h linux/btrfs.h poll.h pwd.h sys/ioctl.h \
+                  sys/ipc.h sys/poll.h sys/pstat.h sys/resource.h \
+                  sys/select.h sys/sem.h sys/shm.h sys/socket.h \
+                  sys/sockio.h sys/tas.h sys/time.h sys/un.h termios.h \
+                  ucred.h utime.h wchar.h wctype.h])

 # On BSD, test for net/if.h will fail unless sys/socket.h
 # is included first.
diff --git a/contrib/pg_upgrade/check.c b/contrib/pg_upgrade/check.c
index 0376fcb..2a52dd8 100644
--- a/contrib/pg_upgrade/check.c
+++ b/contrib/pg_upgrade/check.c
@@ -151,6 +151,9 @@ check_new_cluster(void)
 	if (user_opts.transfer_mode == TRANSFER_MODE_LINK)
 		check_hard_link();

+	if (user_opts.transfer_mode == TRANSFER_MODE_CLONE)
+		check_clone_file();
+
 	check_is_super_user(&new_cluster);

 	/*
diff --git a/contrib/pg_upgrade/file.c b/contrib/pg_upgrade/file.c
index dfeb79f..fc935b7 100644
--- a/contrib/pg_upgrade/file.c
+++ b/contrib/pg_upgrade/file.c
@@ -8,11 +8,16 @@
  */

#include "postgres_fe.h"
+#include "pg_config.h"

#include "pg_upgrade.h"

#include <fcntl.h>

+#ifdef HAVE_LINUX_BTRFS_H
+# include <sys/ioctl.h>
+# include <linux/btrfs.h>
+#endif

#ifndef WIN32
@@ -23,21 +28,42 @@ static int win32_pghardlink(const char *src, const char *dst);

 /*
- * copyAndUpdateFile()
+ * upgradeFile()
  *
- *	Copies a relation file from src to dst.  If pageConverter is non-NULL, this function
- *	uses that pageConverter to do a page-by-page conversion.
+ * Transfer a relation file from src to dst using one of the supported
+ * methods.  If the on-disk format of the new cluster is bit-for-bit
+ * compatible with the on-disk format of the old cluster we can simply link
+ * each relation to perform a true in-place upgrade.  Otherwise we must copy
+ * (either block-by-block or using a copy-on-write clone) the data from old
+ * cluster to new cluster and then perform the conversion.
  */
 const char *
-copyAndUpdateFile(pageCnvCtx *pageConverter,
-				  const char *src, const char *dst, bool force)
+upgradeFile(transferMode transfer_mode, const char *src,
+		const char *dst, pageCnvCtx *pageConverter)
 {
 	if (pageConverter == NULL)
 	{
-		if (pg_copy_file(src, dst, force) == -1)
-			return getErrorText(errno);
-		else
-			return NULL;
+		int rc = -1;
+
+		switch (transfer_mode)
+		{
+			case TRANSFER_MODE_COPY:
+				rc = pg_copy_file(src, dst, true);
+				break;
+			case TRANSFER_MODE_CLONE:
+				rc = upg_clone_file(src, dst);
+				break;
+			case TRANSFER_MODE_LINK:
+				rc = pg_link_file(src, dst);
+				break;
+		}
+
+		return (rc < 0) ? getErrorText(errno) : NULL;
+	}
+	else if (transfer_mode != TRANSFER_MODE_COPY)
+	{
+		return "Cannot in-place update this cluster, "
+			"page-by-page (copy-mode) conversion is required";
 	}
 	else
 	{
@@ -100,29 +126,6 @@ copyAndUpdateFile(pageCnvCtx *pageConverter,
 }

-/*
- * linkAndUpdateFile()
- *
- * Creates a hard link between the given relation files. We use
- * this function to perform a true in-place update. If the on-disk
- * format of the new cluster is bit-for-bit compatible with the on-disk
- * format of the old cluster, we can simply link each relation
- * instead of copying the data from the old cluster to the new cluster.
- */
-const char *
-linkAndUpdateFile(pageCnvCtx *pageConverter,
-				  const char *src, const char *dst)
-{
-	if (pageConverter != NULL)
-		return "Cannot in-place update this cluster, page-by-page conversion is required";
-
-	if (pg_link_file(src, dst) == -1)
-		return getErrorText(errno);
-	else
-		return NULL;
-}
-
-
 #ifndef WIN32
 static int
 copy_file(const char *srcfile, const char *dstfile, bool force)
@@ -228,6 +231,64 @@ win32_pghardlink(const char *src, const char *dst)
 #endif

+int
+upg_clone_file(const char *existing_file, const char *new_file)
+{
+#ifdef BTRFS_IOC_CLONE
+	int rc, res_errno = 0, src_fd = -1, dest_fd = -1;
+
+	src_fd = open(existing_file, O_RDONLY);
+	if (src_fd < 0)
+		return -1;
+
+	dest_fd = open(new_file, O_RDWR | O_CREAT | O_EXCL, S_IRUSR | S_IWUSR);
+	if (dest_fd < 0)
+	{
+		close(src_fd);
+		return -1;
+	}
+
+	rc = ioctl(dest_fd, BTRFS_IOC_CLONE, src_fd);
+	if (rc < 0)
+	{
+		pg_log(PG_REPORT, "btrfs clone: %s\n", strerror(errno));
+		res_errno = errno;  /* save errno for caller */
+		unlink(new_file);
+	}
+
+	close(dest_fd);
+	close(src_fd);
+
+	errno = res_errno;  /* restore errno after close() calls */
+	return rc;
+#else
+	/* TODO: add support for zfs clones */
+	pg_log(PG_REPORT, "system does not support file cloning\n");
+	errno = ENOSYS;
+	return -1;
+#endif
+}
+
+void
+check_clone_file(void)
+{
+	char		existing_file[MAXPGPATH];
+	char		cloned_file[MAXPGPATH];
+
+	snprintf(existing_file, sizeof(existing_file), "%s/PG_VERSION", old_cluster.pgdata);
+	snprintf(cloned_file, sizeof(cloned_file), "%s/PG_VERSION.linktest", new_cluster.pgdata);
+	unlink(cloned_file);		/* might fail */
+
+	if (upg_clone_file(existing_file, cloned_file) == -1)
+	{
+		pg_log(PG_FATAL,
+			   "Could not clone a file between old and new data directories: %s\n"
+			   "File cloning is currently only supported on btrfs.\n",
+			   getErrorText(errno));
+	}
+	unlink(cloned_file);
+}
+
 /* fopen() file with no group/other permissions */
 FILE *
 fopen_priv(const char *path, const char *mode)
diff --git a/contrib/pg_upgrade/option.c b/contrib/pg_upgrade/option.c
index 2774b1e..fdf9f5c 100644
--- a/contrib/pg_upgrade/option.c
+++ b/contrib/pg_upgrade/option.c
@@ -54,6 +54,7 @@ parseCommandLine(int argc, char *argv[])
 		{"retain", no_argument, NULL, 'r'},
 		{"jobs", required_argument, NULL, 'j'},
 		{"verbose", no_argument, NULL, 'v'},
+		{"clone", no_argument, NULL, 1},
 		{NULL, 0, NULL, 0}
 	};
 	int			option;			/* Command line option */
@@ -186,6 +187,10 @@ parseCommandLine(int argc, char *argv[])
 				log_opts.verbose = true;
 				break;

+			case 1:
+				user_opts.transfer_mode = TRANSFER_MODE_CLONE;
+				break;
+
 			default:
 				pg_log(PG_FATAL,
 					   "Try \"%s --help\" for more information.\n",
@@ -236,6 +241,8 @@ Options:\n\
   -D, --new-datadir=DATADIR     new cluster data directory\n\
   -j, --jobs                    number of simultaneous processes or threads to use\n\
   -k, --link                    link instead of copying files to new cluster\n\
+      --clone                   use copy-on-write cloning instead of copying\n\
+                                files to new cluster (only supported on btrfs)\n\
   -o, --old-options=OPTIONS     old cluster options to pass to the server\n\
   -O, --new-options=OPTIONS     new cluster options to pass to the server\n\
   -p, --old-port=PORT           old cluster port number (default %d)\n\
diff --git a/contrib/pg_upgrade/pg_upgrade.h b/contrib/pg_upgrade/pg_upgrade.h
index 0b3ad20..6932bd6 100644
--- a/contrib/pg_upgrade/pg_upgrade.h
+++ b/contrib/pg_upgrade/pg_upgrade.h
@@ -209,12 +209,13 @@ typedef struct
 } ControlData;

/*
- * Enumeration to denote link modes
+ * Enumeration to denote transfer mode
*/
typedef enum
{
TRANSFER_MODE_COPY,
- TRANSFER_MODE_LINK
+ TRANSFER_MODE_LINK,
+ TRANSFER_MODE_CLONE
} transferMode;

/*
@@ -381,12 +382,12 @@ const pageCnvCtx *setupPageConverter(void);
typedef void *pageCnvCtx;
#endif

-const char *copyAndUpdateFile(pageCnvCtx *pageConverter, const char *src,
-				  const char *dst, bool force);
-const char *linkAndUpdateFile(pageCnvCtx *pageConverter, const char *src,
-				  const char *dst);
+const char *upgradeFile(transferMode transfer_mode, const char *src,
+				const char *dst, pageCnvCtx *pageConverter);

 void		check_hard_link(void);
+void		check_clone_file(void);
+int		upg_clone_file(const char *old_file, const char *new_file);
 FILE	   *fopen_priv(const char *path, const char *mode);

 /* function.c */
diff --git a/contrib/pg_upgrade/relfilenode.c b/contrib/pg_upgrade/relfilenode.c
index a951fc9..c808313 100644
--- a/contrib/pg_upgrade/relfilenode.c
+++ b/contrib/pg_upgrade/relfilenode.c
@@ -32,7 +32,10 @@ transfer_all_new_tablespaces(DbInfoArr *old_db_arr, DbInfoArr *new_db_arr,
 							 char *old_pgdata, char *new_pgdata)
 {
 	pg_log(PG_REPORT, "%s user relation files\n",
-	  user_opts.transfer_mode == TRANSFER_MODE_LINK ? "Linking" : "Copying");
+		user_opts.transfer_mode == TRANSFER_MODE_COPY ? "Copying" :
+		user_opts.transfer_mode == TRANSFER_MODE_LINK ? "Linking" :
+		user_opts.transfer_mode == TRANSFER_MODE_CLONE ? "Cloning" :
+		"FAIL");

/*
* Transfering files by tablespace is tricky because a single database can
@@ -270,26 +273,14 @@ transfer_relfile(pageCnvCtx *pageConverter, FileNameMap *map,
/* Copying files might take some time, so give feedback. */
pg_log(PG_STATUS, "%s", old_file);

-		if ((user_opts.transfer_mode == TRANSFER_MODE_LINK) && (pageConverter != NULL))
-			pg_log(PG_FATAL, "This upgrade requires page-by-page conversion, "
-				   "you must use copy mode instead of link mode.\n");
-
-		if (user_opts.transfer_mode == TRANSFER_MODE_COPY)
-		{
-			pg_log(PG_VERBOSE, "copying \"%s\" to \"%s\"\n", old_file, new_file);
-
-			if ((msg = copyAndUpdateFile(pageConverter, old_file, new_file, true)) != NULL)
-				pg_log(PG_FATAL, "error while copying relation \"%s.%s\" (\"%s\" to \"%s\"): %s\n",
-					   map->nspname, map->relname, old_file, new_file, msg);
-		}
-		else
+		msg = upgradeFile(user_opts.transfer_mode, old_file, new_file, pageConverter);
+		if (msg != NULL)
 		{
-			pg_log(PG_VERBOSE, "linking \"%s\" to \"%s\"\n", old_file, new_file);
-
-			if ((msg = linkAndUpdateFile(pageConverter, old_file, new_file)) != NULL)
-				pg_log(PG_FATAL,
-					   "error while creating link for relation \"%s.%s\" (\"%s\" to \"%s\"): %s\n",
-					   map->nspname, map->relname, old_file, new_file, msg);
+			pg_log(PG_FATAL, "error while %s relation \"%s.%s\" (\"%s\" to \"%s\"): %s\n",
+				(user_opts.transfer_mode == TRANSFER_MODE_COPY ? "copying" :
+				 user_opts.transfer_mode == TRANSFER_MODE_LINK ? "linking" :
+				 user_opts.transfer_mode == TRANSFER_MODE_CLONE ? "cloning" :
+				 "FAIL"), map->nspname, map->relname, old_file, new_file, msg);
 		}
 	}

diff --git a/doc/src/sgml/pgupgrade.sgml b/doc/src/sgml/pgupgrade.sgml
index f6cd9f0..fc9b89d 100644
--- a/doc/src/sgml/pgupgrade.sgml
+++ b/doc/src/sgml/pgupgrade.sgml
@@ -126,6 +126,13 @@
      </varlistentry>

      <varlistentry>
+      <term><option>--clone</option></term>
+      <listitem><para>use copy-on-write clones instead of copying or hard linking files to
+      the new cluster; this option can only be used when the old and new clusters reside
+      on the same btrfs filesystem</para></listitem>
+     </varlistentry>
+
+     <varlistentry>
       <term><option>-o</option> <replaceable class="parameter">options</replaceable></term>
       <term><option>--old-options</option> <replaceable class="parameter">options</replaceable></term>
       <listitem><para>options to be passed directly to the
diff --git a/src/include/pg_config.h.in b/src/include/pg_config.h.in
index 8aabf3c..7cd5a8d 100644
--- a/src/include/pg_config.h.in
+++ b/src/include/pg_config.h.in
@@ -317,6 +317,9 @@
 /* Define to 1 if you have the `z' library (-lz). */
 #undef HAVE_LIBZ

+/* Define to 1 if you have the <linux/btrfs.h> header file. */
+#undef HAVE_LINUX_BTRFS_H
+
 /* Define to 1 if constants of type 'long long int' should have the suffix LL.
    */
 #undef HAVE_LL_CONSTANTS
-- 
1.8.3.1

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