6902 speed up listing of snapshots if requesting name only and sorting by name

illumos/illumos-gate@0d8fa8f8eba3ea46bc79d73445009505d1dd5d7d
https://github.com/illumos/illumos-gate/commit/0d8fa8f8eba3ea46bc79d73445009505d1dd5d7d

https://www.illumos.org/issues/6902
  pjd has authored and commited a patch in Jan 21, 2012 that substanially speeds
  up zfs snapshot listing if requesting only the name property and sorting by
  name.
  In this special case, the snapshot properties do not need to be loaded. This
  code has been adopted by zfsonlinux on May 29, 2012.
  Commit message from pjd:
       Dramatically optimize listing snapshots when user requests only
       snapshot
       names and wants to sort them by name, ie. when executes:
          1. zfs list -t snapshot -o name -s name
       Because only name is needed we don't have to read all snapshot
       properties.
       Below you can find how long does it take to list 34509 snapshots from
       a single
       disk pool before and after this change with cold and warm cache:
       before:
          1. time zfs list -t snapshot -o name -s name > /dev/null
             cold cache: 525s
             warm cache: 218s
       after:
          1. time zfs list -t snapshot -o name -s name > /dev/null
             cold cache: 1.7s
             warm cache: 1.1s
  References:
  http://svnweb.freebsd.org/base?view=revision&revision=230438
  https://github.com/freebsd/freebsd/commit/8e3e9863
  https://github.com/zfsonlinux/zfs/commit/0cee2406

Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Pawel Dawidek <pjd@freebsd.org>
Reviewed by: Brian Behlendorf <behlendorf1@llnl.gov>
Approved by: Garrett D'Amore <garrett@damore.org>
Author: Martin Matuska <martin@matuska.org>

1 files changed, 2 insertions, 1 deletions

diff --git a/lib/libzfs/common/libzfs.h b/lib/libzfs/common/libzfs.h
index 3cbfe35d5287..75ac241382f9 100644
--- a/lib/libzfs/common/libzfs.h
+++ b/lib/libzfs/common/libzfs.h
@@ -21,6 +21,7 @@
 
 /*
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2011 Pawel Jakub Dawidek. All rights reserved.
  * Copyright (c) 2011, 2015 by Delphix. All rights reserved.
  * Copyright (c) 2012, Joyent, Inc. All rights reserved.
  * Copyright (c) 2013 Steven Hartland. All rights reserved.
@@ -534,7 +535,7 @@ extern int zfs_iter_root(libzfs_handle_t *, zfs_iter_f, void *);
 extern int zfs_iter_children(zfs_handle_t *, zfs_iter_f, void *);
 extern int zfs_iter_dependents(zfs_handle_t *, boolean_t, zfs_iter_f, void *);
 extern int zfs_iter_filesystems(zfs_handle_t *, zfs_iter_f, void *);
-extern int zfs_iter_snapshots(zfs_handle_t *, zfs_iter_f, void *);
+extern int zfs_iter_snapshots(zfs_handle_t *, boolean_t, zfs_iter_f, void *);
 extern int zfs_iter_snapshots_sorted(zfs_handle_t *, zfs_iter_f, void *);
 extern int zfs_iter_snapspec(zfs_handle_t *, const char *, zfs_iter_f, void *);
 extern int zfs_iter_bookmarks(zfs_handle_t *, zfs_iter_f, void *);