[#1483] metabase: Add VERSION.md

Signed-off-by: Evgenii Stratonikov <evgeniy@nspcc.ru>

pkg/local_object_storage/metabase/VERSION.md

@@ -0,0 +1,87 @@
+# Metabase versioning
+
+This file describes changes between the metabase versions.
+
+## Version 0
+
+- Container ID is encoded as base58 string
+- Object ID is encoded as base58 string
+- Address is encoded as container ID + "/" + object ID
+
+### Primary buckets
+- Graveyard bucket
+  - Name: `_Graveyard`
+  - Key: object address 
+  - Value: tombstone address
+- Garbage bucket
+  - Name: `_Garbage`
+  - Key: object address
+  - Value: dummy value
+- Bucket containing IDs of objects that are candidates for moving
+   to another shard.
+  - Name: `_ToMoveIt`
+  - Key: object address
+  - Value: dummy value
+- Container volume bucket
+  - Name: `_ContainerSize`
+  - Key: container ID
+  - Value: container size in bytes as little-endian uint64
+- Bucket for storing locked objects information
+  - Name: `_Locked` 
+  - Key: container ID
+  - Value: bucket mapping objects locked to the list of corresponding LOCK objects
+- Bucket containing auxilliary information. All keys are custom and are not connected to the container
+  - Name: `_i`
+  - Keys and values
+    - `id` -> shard id as bytes
+    - `version` -> metabase version as little-endian uint64
+
+### Unique index buckets
+- Buckets containing objects of REGULAR type
+  - Name: container ID
+  - Key: object ID
+  - Value: marshalled object
+- Buckets containing objects of LOCK type
+  - Name: container ID + `_LOCKER`
+  - Key: object ID
+  - Value: marshalled object
+- Buckets containing objects of STORAGEGROUP type
+  - Name: container ID + `_SG`
+  - Key: object ID
+  - Value: marshaled object
+- Buckets containing objects of TOMBSTONE type
+  - Name: container ID + `_TS`
+  - Key: object ID
+  - Value: marshaled object
+- Buckets mapping objects to the blobovniczas they are stored in
+  - Name: container ID + `_small`
+  - Key: object ID
+  - Value: blobovnicza ID
+- Buckets for mapping parent object to the split info
+  - Name: container ID + `_root`
+  - Key: object ID
+  - Value: split info
+
+### FKBT index buckets
+- Buckets mapping owner to object IDs
+  - Name: containerID + `_ownerid`
+  - Key: owner ID as base58 string
+  - Value: bucket containing object IDs as keys
+- Buckets containing objects attributes indexes
+  - Name: containerID + `_attr_` + attribute key
+  - Key: attribute value
+  - Value: bucket containing object IDs as keys
+
+### List index buckets
+- Buckets mapping payload hash to a list of object IDs
+  - Name: container ID + `_payloadhash`
+  - Key: payload hash
+  - Value: list of object IDs
+- Buckets mapping parent ID to a list of children IDs
+  - Name: container ID + `_parent`
+  - Key: parent ID
+  - Value: list of children object IDs
+- Buckets mapping split ID to a list of object IDs
+  - Name: container ID + `_splitid`
+  - Key: split ID
+  - Value: list of object IDs