Nathan Vander Wilt created COUCHDB-1682:
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Summary: Allow filtered _changes to time out, returning last_seq
processed
Key: COUCHDB-1682
URL: https://issues.apache.org/jira/browse/COUCHDB-1682
Project: CouchDB
Issue Type: Improvement
Reporter: Nathan Vander Wilt
Right now a filtered _changes query ?since=0 on a database with a high
update_seq can take a very long time to return. If this request is performed
through a proxy or through a browser with a timeout, it may never complete as
far as the client is concerned.
Right now CouchDB itself ignores any polling timeout for such a request — i.e.
it does not time out while the _changes results are still processing. This is
okay, as it at least lets patient clients get a result.
I propose, though, that the timeout value be respected during the "initial"
(e.g. in the context of a fresh replication) request. When the timeout is
reached, the client should get back a valid response, with incomplete (even
empty!) results and a last_seq corresponding to how far it had processed
changes in the background. Then the client/replicator could record a checkpoint
and request processing of the next batch.
The net result would be that the initial replication request would not be
unbounded in time. Even if a response is "timed out" by a proxy/browser within
30 seconds or 5 minutes, assuming the client is aware of this limit they could
set a bit lower timeout and get back a last_seq that keeps them from having to
(futile-ly) try again from since=0.
Unfortunately, this does slightly change the semantics of the query: it is as
if limit=0 when the client provided no (or a different) limit and may be
expecting last_seq to ± match current_seq for such a request. So perhaps this
behaviour would need to be enabled by its own query parameter, ?batch=please or
something.
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