PendingReleaseNotes: note about changing omap backend to rocksdb

Signed-off-by: Josh Durgin <jdurgin@redhat.com>

diff --git a/PendingReleaseNotes b/PendingReleaseNotes
index c0abc91883d1a7805da7770837ef374573014997..d134ac86ad2b2a23ee1bd37c6f569014eada75cb 100644 (file)
--- a/PendingReleaseNotes
+++ b/PendingReleaseNotes
@@ -15,3 +15,10 @@
 * The RBD C API's rbd_discard method and the C++ API's Image::discard method
   now enforce a maximum length of 2GB. This restriction prevents overflow of
   the result code.
+
+* New OSDs will now use rocksdb for omap data by default, rather than
+  leveldb. omap is used by RGW bucket indexes and CephFS directories,
+  and when a single leveldb grows to 10s of GB with a high write or
+  delete workload, it can lead to high latency when leveldb's
+  single-threaded compaction cannot keep up. rocksdb supports multiple
+  threads for compaction, which avoids this problem.