Alexander Shorin created COUCHDB-2961:
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Summary: Let heartbeat work together with timeout for changes feed
Key: COUCHDB-2961
URL: https://issues.apache.org/jira/browse/COUCHDB-2961
Project: CouchDB
Issue Type: Improvement
Components: HTTP Interface
Reporter: Alexander Shorin
What do we have now.
Changes feeds accepts two query parameters: heartbeat and timeout. The
heartbeat defines interval of sending heartbeat events (the {{\n}} for
continuous and longpoll feeds, special event for eventsource one). The timeout
defines the max time to wait for the changes and if nothing happened, CouchDB
terminates the feed.
When you specify heartbeat with timeout together, say
{{http://localhost:5984/db/_changes?heartbeat=1000&timeout=5000&feed=continuous}}
I guess everyone would expect that we want to receive heartbeats every 1
second and terminate the feed after 5 seconds of inactivity. However, timeout
parameter will get ignored and we'll receive heartbeat every second forever.
How it should work:
Assume we want to listen continuous changes feed, receive heartbeats every 3
seconds and terminate the feed after 10 seconds of inactivity. Then the request
will be sort of:
{code}
http://localhost:5984/db/_changes?feed=continuous&timeout=10000&heartbeat=3000
{code}
And our expected communication:
{code}
- - C - - - H - - - H - C - - - H - - - H - - - H - T
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6
0 1 2
Legend:
C - change event
H - heartbeat
T - termination
{code}
So what we need is to not reset timeout timer by sending heartbeats, but do
that by sending real document changes.
Actually, current implementation swallow timeout parameter, replacing it with
heartbeat value and replaces callback that stops the feed with the one that
generates heartbeats. The fix should be trivial.
To preserve backward compatibility we may use default timeout as infinity (the
code already supports that) if only heartbeat was explicitly specified.
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