[GitHub] [couchdb] nickva opened a new issue #3885: Changes feed rewinds when a shard is moved to new node with no subsequent updates

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

nickva opened a new issue #3885:
URL: https://github.com/apache/couchdb/issues/3885


   When shards are moved to new nodes we record ownership in an epoch history list in the db shard file. The epoch list looks like `[{node2, seq2}, {node1, seq1}, ...]`. The epoch list is updated when we open the shard on the new node for the first time.
   
   However, if the db on the new node is never updated, such that the current update sequence matches exactly the one when ownership was transferred to the new node, we end re-winding the changes sequence all the way to the previous epoch (usually 0 if this is the first shard move).
   
   The reason seems to be that we use a strictly greater than comparison during the [epoch ownership check](https://github.com/apache/couchdb/blob/3.x/src/couch/src/couch_db.erl#L1796-L1797):
   ```erlang
   owner_of([{EpochNode, EpochSeq} | _Rest], Seq) when Seq > EpochSeq ->
   ```
   
   
   
   


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[GitHub] [couchdb] nickva closed issue #3885: Changes feed rewinds when a shard is moved to new node with no subsequent updates

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

nickva closed issue #3885:
URL: https://github.com/apache/couchdb/issues/3885


   


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