incubator-couchdb-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Robert Newson <rnew...@apache.org>
Subject Re: When is _replicate synchronous?
Date Thu, 20 Jun 2013 17:53:14 GMT
the id version reflects an internal detail. The scheme for deriving
replication ids changes over time but to prevent redo-from-start,
we'll look for values generated with older versions of the scheme in
the event of a miss (a missing _local checkpoint doc).

Is it necessary to CC Filipe's work email address? His apache.org
address should receive this.

B.


On 20 June 2013 18:51, Robert Newson <rnewson@apache.org> wrote:
> _replicate was always a blocking call, and then we added continuous
> replication. Obviously it then makes no sense to wait for "the end".
>
> B.
>
>
> On 20 June 2013 18:41, Jens Alfke <jens@couchbase.com> wrote:
>> The wiki docs for _replicate don’t say so, but in practice the call appears to
be synchronous unless the ‘continuous’ property is set. That is, it doesn’t return a
response until the replication completes, and in fact the response JSON includes a bunch of
statistics about the replication.
>>
>> I didn’t know this when I implemented TouchDB, so I made _replicate always asynchronous.
(It made more sense to me, especially since my client code needed to be able to track the
progress of a replication using _active_tasks, which meant it needed a response ASAP so it
could get the task ID.)
>>
>> I’m amending this now for Couchbase Lite, but I’d like to make sure I know the
semantics. Is it true that it’s always synchronous unless continuous=true, and then it’s
asynchronous?
>>
>> Also, is there any description somewhere of what the properties in the synchronous
response mean? Some are obvious, some less so. Here’s an example from 1.2:
>>
>>  {
>>     "history": [
>>         {
>>             "doc_write_failures": 0,
>>             "docs_read": 18,
>>             "docs_written": 18,
>>             "end_last_seq": 19,
>>             "end_time": "Thu, 20 Jun 2013 16:58:13 GMT",
>>             "missing_checked": 18,
>>             "missing_found": 18,
>>             "recorded_seq": 19,
>>             "session_id": "1cef7405d0e61fb0decc89323669a012",
>>             "start_last_seq": 0,
>>             "start_time": "Thu, 20 Jun 2013 16:58:13 GMT"
>>         }
>>     ],
>>     "ok": true,
>>     "replication_id_version": 2,
>>     "session_id": "1cef7405d0e61fb0decc89323669a012",
>>     "source_last_seq": 19
>> }
>>
>> I’m particularly curious (a) why “history” is an array, and (b) what “replication_id_version”
means.
>>
>> —Jens

Mime
View raw message