[GitHub] jiangphcn commented on a change in pull request #1676: Downgrade code for Database partitions

[GitBox <gi...@apache.org>]

jiangphcn commented on a change in pull request #1676: Downgrade code for Database partitions
URL: https://github.com/apache/couchdb/pull/1676#discussion_r227666512
 
 

 ##########
 File path: src/couch/src/couch_bt_engine.erl
 ##########
 @@ -857,6 +868,59 @@ init_state(FilePath, Fd, Header0, Options) ->
     end.
 
 
+downgrade_partition_info(Header) ->
+    % {db_header,
+    %     disk_version = ?LATEST_DISK_VERSION,
+    %     update_seq = 0,
+    %     unused = 0,
+    %     id_tree_state = nil,
+    %     seq_tree_state = nil,
+    %     local_tree_state = nil,
+    %     purge_tree_state = nil,
+    %     purge_seq_tree_state = nil, %purge tree: purge_seq -> uuid
+    %     security_ptr = nil,
+    %     revs_limit = 1000,
+    %     uuid,
+    %     epochs,
+    %     compacted_seq,
+    %     purge_infos_limit = 1000,
+    %     props_ptr
+    % },
+    {
+        db_header,
+        _DiskVer,
+        UpSeq,
+        _Unused,
+        IdTreeState,
+        SeqTreeState,
+        LocalTreeState,
+        PurgeTreeState,
+        PurgeSeqTreeState,
+        SecurityPtr,
+        RevsLimit,
+        Uuid,
+        Epochs,
+        CompactedSeq,
+        _PDocsLimit,
+        _PropsPtr
+    } = Header,
+     
+    NewHeader = couch_bt_engine_header:new(),
+    couch_bt_engine_header:set(NewHeader, [
+        {update_seq, UpSeq},
+        {id_tree_state, IdTreeState},
+        {seq_tree_state, SeqTreeState},
+        {local_tree_state, LocalTreeState},
+        {purge_tree_state, PurgeTreeState},
+        {purge_seq_tree_state, PurgeSeqTreeState},
+        {security_ptr, SecurityPtr},
+        {revs_limit, RevsLimit},
+        {uuid, Uuid},
+        {epochs, Epochs},
+        {compacted_seq, CompactedSeq}
 
 Review comment:
   The value of `purge_infos_limit` can be changed and may not be default. So there is need to write current value to database header as well. 

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