Can a CouchDB document update handler get an update conflict?

Answer 1

Update conflicts are still possible when using update handlers.

Due to the reduced "round-trip time," the chance of an update conflict is lower but not zero. A conflict will feel normal: a 409 response code with this JSON:

{"error":"conflict","reason":"Document update conflict."}

I successfully triggered a conflict using the document update handler example, and running curl twice in short succession in the shell.

curl -v -X PUT \
http://localhost:5984/db/_design/app/_update/accumulate/my_doc?amount=10 \
& curl -X PUT \
  http://localhost:5984/db/_design/app/_update/accumulate/my_doc?amount=1

One of the curl responses (randomly) was a 201 and the other a 409.

Document update handlers do not fundamentally change CouchDB

Updates are subject to conflicts, as well as validation failures (401 Unauthorized, 403 Forbidden, etc.)