On Tue, Jan 27, 2009 at 11:45 AM, Matt Goodall <[email protected]> wrote:
> 2009/1/27 Chris Anderson <[email protected]>:
>> On Tue, Jan 27, 2009 at 5:30 AM, Matt Goodall <[email protected]> wrote:
>>> Hi,
>>>
>>> Both the wiki, http://wiki.apache.org/couchdb/Compaction, and Futon
>>> warn that compacting removes deleted documents. However, a deleted
>>> document is still represented in _all_docs_by_seq after compaction.
>>
>> Perhaps the wording should be more clear. Compaction removes old revs
>> of all documents. So in the case of a deleted document, the head rev
>> is the one that marks it as deleted, but before compaction, the
>> original version of the document (in your example, rev 143469513) is
>> kept in the file. After compaction, only the latest rev remains.
>
> Yeah, that was pretty much my understanding of it until I read the
> wiki and noticed Futon's warning. (Although I had to double check to
> make sure!)
>
>>
>> Compaction preserves any conflict-revs as well.
>
> So, if we were to fix the wording, are there any other issues you can
> think of other than:
>
> a) old revisions will be removed which may make it difficult to
> correct conflicts
> b) it can take a very long time on large documents
>
Compaction works by recopying the still-valid nodes from the old
database file to a new database file. So it will take longer for large
dbs. Under heavy write load, it is possible that compaction can never
complete, unless write load is abated for a moment to allow compaction
to finish and swap the new file for the old.
It's essentially a form of on-disk generational garbage collection.
>>
>>>
>>> $ curl -X "PUT" -d "{}" "http://localhost:5984/compaction/doc";
>>> {"ok":true,"id":"doc","rev":"143469513"}
>>> $ curl -X "DELETE" "http://localhost:5984/compaction/doc?rev=143469513";
>>> {"ok":true,"id":"doc","rev":"1135956802"}
>>> $ curl -X "POST" "http://localhost:5984/compaction/_compact";
>>> {"ok":true}
>>> $ curl "http://localhost:5984/compaction/_all_docs_by_seq";
>>> {"total_rows":0,"offset":0,"rows":[
>>> {"id":"doc","key":2,"value":{"rev":"1135956802","deleted":true}}
>>> ]}
>>>
>>> Presumably, the wiki & Futon are incorrect as it makes complete sense
>>> to keep deleted documents around for replication, but I'll wait for a
>>> response to this email before I create a ticket.
>>>
>>> - Matt
>>>
>>
>>
>>
>> --
>> Chris Anderson
>> http://jchris.mfdz.com
>>
>
--
Chris Anderson
http://jchris.mfdz.com
