Couchbase deleted documents reappearing in database

Question

We are experiencing a problem where deleted documents are reappearing on our Couchbase server.

We have a scenario where documents are created on CBL. These documents are synced up to the server. The user realizes an error has been made and flags the document as incorrect. On the server the admin can then view all of the flagged documents and delete them from the server. The sync gateway has been setup to only sync up these types of documents, i.e. once an edit has been made to these documents on the server the changes are not synced back down to CBL.

Here is the process of what is happening:

Document is created on CBL with a TTL of 15 days and synced to sync
Document is updated on CBL and synced to sync gateway.
Document is deleted from the Couchbase Server bucket with a DELETE N1QL query.
After the document is deleted from the bucket it gets randomly added again within a few days.
Only documents that are still on the devices i.e. not older than TTL of 15 days, are added back to the bucket.

We tried increasing the Metadata Purge Interval to more than 15 days but this did not resolve the problem.

Does anybody have any suggestions or possibly know what could be the problem here?

Couchbase Server Community Edition 6.5.1 build 6299
Sync gateway 2.7.3
Couchbase Lite Android 2.8.1

Thanks in advance!

PS: Here is our Sync Gateway config with the sync function:

    "log": [
        "*"
    ],
    "adminInterface": "0.0.0.0:4985",
    "interface": "0.0.0.0:4984",
    "databases": {
        "prod": {
            "server": "http://localhost:8091",
            "bucket": "prod_bukcet",
            "username": "sync_gateway",
            "password": "XXX",
            "enable_shared_bucket_access": true,
            "import_docs": "continuous",
            "use_views": true,
            "users": {
                "user_X": {
                    "password": "XXX",
                    "admin_channels": ["*"],
                    "disabled": false
                }
            },
            "sync":`
                function sync(doc, oldDoc) {
                    /* sanity check */
                    // check if document was removed from server or via SDK
                    // In this case, just return
                    if (isRemoved()) {
                        return;
                    }
                    //Only sync down documents that are created on the server
                    if (doc.deviceDoc == true) {
                        channel("server");
                    } else {
                        if (doc.siteId) {
                            channel(doc.siteId);
                        } else {
                            channel("devices");
                        }
                    }
                    // This is when document is removed via SDK or directly on server
                    function isRemoved() {
                        return (isDelete() && oldDoc == null);
                    }
                    function isDelete() {
                        return (doc._deleted == true);
                    }
                }`,
        }
    }
}

rajagp rajagp · Accepted Answer · 2021-02-16T23:36:47

In shared bucket access mode (enable_shared_bucket_access:true),a N1QL delete on a document creates a tombstone. Tombstones are always synced. The metadata purge interval setting on the server determines the period after which the tombstone gets purged on the server. So it is typical to set it to a value that matches the maximum partition window of the client- that is to ensure that all disconnected clients have the opportunity to get the deleted document. So setting it to > 15 days just means that the tombstone will be purged after 15 days and so tombstoned documents will be synced down to clients in the meantime.

In your case, if you don't want documents to be synced down to clients because the lifetime of the document is managed independently on CBL side via the expirationDate(), then purge the document instead of deleting it on server.

Couchbase deleted documents reappearing in database

1 Answers