Hi,
I think this issue was raised a couple months ago but I am not
sure what, if anything, has been done to address it or even
whether it was formally entered into JIRA.
Given the push for a 1.0.2 release, I wanted to raise it as an
issue for consideration for the 1.0.2 release.
The problem is basically this: when a change filter is busy
processing documents, the heartbeat will not be sent across the
wire. This plays havoc with clients listening on those feeds
because the sockets can eventually time out.
This might seem like an unlikely pathological situation, but
consider a network of couch servers front ended by one or more
application servers. The app servers listen on change
notifications to pick up messages from other apps/couch
servers. An app server does not want to "read" its own writes,
and so a filter is used.
In a busy system in which one server is producing most or all of
the documents, the change feed can die quickly and often.
In a busy system, this failure mode can have unintended
consequences by creating feedback loops on the app and database
servers, as well as the system as a whole, when the clients
attempt to reconnect (and then fail eventually and then
reconnect and so on).
Obviously, I am describing a specific system implementation,
which needs more built-in protections against this failure mode,
but solving the heartbeat problem would prevent that mode in the
first place :)
I'm eager to have this problem fixed and would be willing to
take a shot at it if someone could provide a bit of guidance.
The problem is easily reproducible in a pathological scenario
like this:
1. Create a database named "test"
2. Attach a filter to the database:
{
"language": "erlang",
"views": {
},
"filters": {
"test": "fun({Doc}, _) ->\n false end."
}
}
3. Open up a continuous feed using that filter.
curl
"localhost:5984/test/_changes?filter=test/test&feed=continuous&heartbeat=5000"
4. Write many docs into the database
(one of my test scripts)
#!/bin/sh
COUNTER=0
while [ $COUNTER -lt 3000 ]; do
ITS=0
while [ $ITS -lt 5 ]; do
PAYLOAD="{\"docType\":\"CS_MANIFEST\",
\"contentSetPath\":\"/some/path/${COUNTER}/${ITS}\",
\"versionName\":\"$COUNTER\", \"linkDate\":123456789${COUNTER}}"
curl -X POST -d "$PAYLOAD" -H
"Content-Type:application/json" http://localhost:5984/test
let ITS=ITS+1
done
let COUNTER=COUNTER+1
done
5. Notice the heartbeat stops until the script has completed
Matt
