Fast Clone Deletion

Deleting a clone requires finding blocks are clone-only, not shared
with the snapshot. This was done by traversing the entire block tree
which results in a large performance penalty for sparsely
written clones.

This is new method keeps track of clone blocks when they are
modified in a "Livelist" so that, when it’s time to delete,
the clone-specific blocks are already at hand.

We see performance improvements because now deletion work is
proportional to the number of clone-modified blocks, not the size
of the original dataset.

Reviewed-by: Sean Eric Fagan <[email protected]>
Reviewed-by: Matt Ahrens <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: Serapheim Dimitropoulos <[email protected]>
Signed-off-by: Sara Hartse <[email protected]>
Closes #8416 

1 files changed, 20 insertions, 1 deletions

diff --git a/man/man5/zpool-features.5 b/man/man5/zpool-features.5
index 444a996e1..00bad9f74 100644
--- a/man/man5/zpool-features.5
+++ b/man/man5/zpool-features.5
@@ -550,6 +550,26 @@ improving performance by avoiding the use of spill blocks.
 .sp
 .ne 2
 .na
+\fB\fBlivelist\fR\fR
+.ad
+.RS 4n
+.TS
+l l .
+GUID	com.delphix:livelist
+READ\-ONLY COMPATIBLE	yes
+DEPENDENCIES	none
+.TE
+This feature allows clones to be deleted faster than the traditional method
+when a large number of random/sparse writes have been made to the clone.
+All blocks allocated and freed after a clone is created are tracked by the
+the clone's livelist which is referenced during the deletion of the clone.
+The feature is activated when a clone is created and remains active until all
+clones have been destroyed.
+.RE
+
+.sp
+.ne 2
+.na
 \fBlz4_compress\fR
 .ad
 .RS 4n
@@ -882,7 +902,6 @@ This feature becomes \fBactive\fR when the \fBzpool checkpoint\fR subcommand
 is used to checkpoint the pool.
 The feature will only return back to being \fBenabled\fR when the pool
 is rewound or the checkpoint has been discarded.
-.RE
 
 .SH "SEE ALSO"
 zpool(8)