Merge tag '2.15.0+ds1' into debian/victoria

diff --cc NEWS
index d357da31d8778e49020d38c1d9d19f22c6c33d0d,bc901efdb1195d874611b09719e3679e092c30b4..1591087c4b2e42e29de7fcf6d11b4725d97d43fa
--- 1/NEWS
--- 2/NEWS
+++ b/NEWS
@@@ -1,6 -1,14 +1,14 @@@
 -v2.15.0 - 15 Feb 2021
 +Post-v2.14.0
  ---------------------
     - OVSDB:
+      * Changed format in which ovsdb transactions are stored in database files.
+        Now each transaction contains diff of data instead of the whole new
+        value of a column.
+        New ovsdb-server process will be able to read old database format, but
+        old processes will *fail* to read database created by the new one.
+        For cluster and active-backup service models follow upgrade instructions
+        in 'Upgrading from version 2.14 and earlier to 2.15 and later' section
+        of ovsdb(7).
       * New unixctl command 'ovsdb-server/get-db-storage-status' to show the
         status of the storage that's backing a database.
       * New unixctl command 'ovsdb-server/memory-trim-on-compaction on|off'.