Mdbx: WriteMap fallback on open error (#369)

* save

* save

Author: AskAlexSharov

kv/mdbx/kv_mdbx.go

@@ -231,7 +231,12 @@ func (opts MdbxOpts) Open() (kv.RwDB, error) {
 
 	err = env.Open(opts.path, opts.flags, 0664)
 	if err != nil {
-		return nil, fmt.Errorf("%w, label: %s, trace: %s", err, opts.label.String(), stack2.Trace().String())
+		log.Warn("error at db.open likely because of https://github.com/erthink/libmdbx/issues/269#issuecomment-1068214834 (our advise: use linux > 5.4), now we adding WriteMap option and retry", "err", err)
+		opts.flags |= mdbx.WriteMap
+		err = env.Open(opts.path, opts.flags, 0664)
+		if err != nil {
+			return nil, fmt.Errorf("%w, label: %s, trace: %s", err, opts.label.String(), stack2.Trace().String())
+		}
 	}
 
 	if opts.syncPeriod != 0 {