commitlog: Open files with append_is_unlikely
commitlog: Open files with append_is_unlikely

This open option tells seastar that the file in question
will be truncated to the needed size right at once and all
the subsequent writes will happen within this size. This
hint turns off append optimization in seastar that's not
that cheap and helps so save few cpu cycles.

The option was introduced in seastar by 8bec57bc.

tests: unit(dev), dtest(commitlog:
                        test_batch_commitlog,
                        test_periodic_commitlog,
                        test_commitlog_replay_on_startup)

Signed-off-by: Pavel Emelyanov <c9a32589e048e044184536f7ac71ef92fe82df3e@scylladb.com>
Message-Id: <20210323115409.31215-1-c9a32589e048e044184536f7ac71ef92fe82df3e@scylladb.com>

scylladb/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla