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https://issues.apache.org/jira/browse/COUCHDB-650?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12832869#action_12832869
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Randall Leeds commented on COUCHDB-650:
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"The problem with since=now is that it can lead to missed updates."
This statement is true only under the assumption that the client cares about
old updates, which may not be the case.
I submit that this patch is non-essential (hence "Improvement"). It is always
possible to query /db to get the current seq. However, in my head I see the
potential for since=now to become a common usage pattern that avoids an extra
GET.
My particular use case involves a clustering scenario (specifically, Lounge) in
which I am streaming _changes notifications from all shards and returning an
opaque token that encodes the seq number for every shard. When the redundancy
configuration changes the server has a few options when encountering a ?since
request that doesn't entirely specify where to begin listening on every shard.
1) The server uses ?since=0 on the shards of which the client has no knowledge.
Clearly not okay with a large history.
2) The server issues a /db request to the unspecified shard in order to start
from "now".
I was just trying to create a shortcut for the now case, which would simplify
the logic of the server. After I received reasonably enthusiastic feedback from
those present on IRC I wrote the quick patch.
Again, non-essential. If there's a clear non-inclusion policy toward
non-essential features like this, I understand if you refuse it. As I see it,
it doesn't complicate the API significantly because it reuses the ?since
parameter. I wonder now how many people would actually find this useful.
We probably shouldn't dwell on something so small for too long. So, Chris, I'm
happy for you to just make the call. Feel free to close as wont-fix or apply as
you see fit.
> Add "now" option for ?since parameter on _changes
> -------------------------------------------------
>
> Key: COUCHDB-650
> URL: https://issues.apache.org/jira/browse/COUCHDB-650
> Project: CouchDB
> Issue Type: Improvement
> Components: HTTP Interface
> Reporter: Randall Leeds
> Priority: Minor
> Attachments:
> 0001-add-since-now-option-to-continuous-catch-edge-cases-.patch
>
>
> As per a discussion on IRC with mikeal, jan_____, whartung, and rnewson:
> Having _changes?since="now" allows clients to listen to only new changes
> without making two requests (one to extract seq from /db, and one _changes).
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