nono opened a new issue #2501: Corrupted database where a document has 2 root revisions URL: https://github.com/apache/couchdb/issues/2501 ## Description I don't know what happened, but I have a database where some documents are in a very weird state. Let's take one of those documents: ``` $ curl -s "http://couch:5984/cozyxxxxxxxxxxxxxxxxxxxxxxx%2Fio-cozy-files/78ca2b76808dd591f1b64f1f137bfe48?meta=true&revs=true&open_revs=all"; --41adad57f1b406a22332b1bc52b378c4 Content-Type: application/json {"_id":"78ca2b76808dd591f1b64f1f137bfe48","_rev":"5-bc7fe0c9fec74c7d857d17e97121aebe","cozyMetadata":{"doctypeVersion":"1","metadataVersion":1,"createdAt":"2020-01-10T17:18:59.681880993Z","createdByApp":"cozy-desktop","createdByAppVersion":"3.17.0","updatedAt":"2020-01-10T17:20:02.966474161Z","createdOn":"https://xxxxxx.mycozy.cloud/"},"created_at":"2020-01-10T17:18:59Z","dir_id":"3ec8cdd199d7081a9361f46c22615721","name":"[REDACTED]","path":"/[REDACTED]","tags":[],"type":"directory","updated_at":"2020-01-10T17:18:59Z","_revisions":{"start":5,"ids":["bc7fe0c9fec74c7d857d17e97121aebe","ed6c725a3249ce90ce4155d0180d3c07","9e0c917a7719b181293c22207a54e195","cf252a1dfa81712e140c3b9b2fa25347","90d8ea315491928e8f3199360a0a48bd"]}} --41adad57f1b406a22332b1bc52b378c4 Content-Type: application/json {"_id":"78ca2b76808dd591f1b64f1f137bfe48","_rev":"11-9236dbe8f2baf8e5a1384fa64bd61545","_deleted":true,"_revisions":{"start":11,"ids":["9236dbe8f2baf8e5a1384fa64bd61545","62ceec92c6557ab036ec6a808dba8b8a","b5c87beae0e88912edcfab866d32fd6f","a0e1231615202ba37adb60179e8373d0","e7cadf01aae5cab26d71b6e7405f0e35","2a0151e2c632e15f7584d94ea2520449","bc7fe0c9fec74c7d857d17e97121aebe","ed6c725a3249ce90ce4155d0180d3c07","9e0c917a7719b181293c22207a54e195","cf252a1dfa81712e140c3b9b2fa25347","845faf29d2ab2d455c8f47948062676b"]}} --41adad57f1b406a22332b1bc52b378c4-- ``` CouchDB tells me that there is a conflict on this document, with 2 branches. The branch for `11-9236dbe8f2baf8e5a1384fa64bd61545` has lost the conflict, as it is marked as `_deleted`. And the other branch ends with `5-bc7fe0c9fec74c7d857d17e97121aebe`. But, when looking at the `_revisions`, we can see that `5-bc7fe0c9fec74c7d857d17e97121aebe` is an ancestor of `11-9236dbe8f2baf8e5a1384fa64bd61545`. So, there should be no conflict. And, the really weird thing: both branches have the same revisions 5, 4, 3, and 2, but their first revisions are not the same: `90d8ea315491928e8f3199360a0a48bd` and `845faf29d2ab2d455c8f47948062676b`. I don't understand how the internal structures of CouchDB for storing the revisions tree can give us two roots. By the way, I also got: ``` "_revs_info": [ { "rev": "5-bc7fe0c9fec74c7d857d17e97121aebe", "status": "missing" }, ``` I think that this revision was compacted on some nodes of the cluster, but not on others. ## Steps to Reproduce I don't know how to reproduce. I understand that without a way to reproduce, it would be very hard to fix the bug. For the moment, I'd like to understand how it is possible that CouchDB sees two roots in a revision tree, and why a revision that is ancestor of another revision can be seen as a leaf. ## Expected Behaviour Well, first, I would have expected that CouchDB enforces that the revisions for a document are a tree. And, that a revision listed in `_revisions` for another revision cannot be seen as a leaf. And that leaf revisions cannot be missing (compacted). ## Your Environment * CouchDB version used: 2.3.0 * Operating system and version: Debian 9.11 ```json {"couchdb":"Welcome","version":"2.3.0","git_sha":"07ea0c7","uuid":"b3ac19e755fb8720ec0be49b61086e87","features":["pluggable-storage-engines","scheduler"],"vendor":{"name":"The Apache Software Foundation"}} ```` ## Additional Context To fix a document, we can go this way: 1. Add a new revision to the `_deleted` branch 2. Compact the database 3. Purge the old revisions 4. Delete again the document But it's a manual operation. And it doesn't explain how we were in this situation.
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