couchdb-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Robert Newson <rnew...@apache.org>
Subject Re: Compaction Best Practices
Date Thu, 14 Jun 2012 14:47:03 GMT
The scheme I suggest avoids compaction entirely, which I thought was
your main struggle.

You still need to delete the documents in the old database so that you
can detect when it's safe to delete it. When it's empty, -X DELETE it.
A database delete is a simple 'rm' of the file, taking very little
time.

You can ignore the revs_limit suggestions since you don't update the
documents. And you should ignore it even if you do, there's almost no
legitimate case for altering that setting.

B.

On 14 June 2012 15:21, Tim Tisdall <tisdall@gmail.com> wrote:
> The deleting doesn't take too much time, it's the compaction process,
> right?  If you have a different DB for each day, then you could
> compact previous days without affecting writing to the current day.
> Also, once you've completely deleted all the records from a previous
> days set of logs, you could then proceed to just delete that day's
> database instead of compacting it.
>
>
> On Thu, Jun 14, 2012 at 9:30 AM, Nicolas Peeters <nicolists@gmail.com> wrote:
>> A few more hints, after investigation with the team.
>> 1. We can't really have rotating DBs as sometimes we want to keep older
>> transaction records in the DB for a longer time.
>> 2. We never replicate nor update the statements (so the _rev_limit won't
>> really change much (or will it for the compaction??))
>>
>> On Thu, Jun 14, 2012 at 3:14 PM, Nicolas Peeters <nicolists@gmail.com>wrote:
>>
>>> Actually we never modify those records. Just query them up in certain
>>> cases.
>>>
>>> Regarding Robert's suggestion, I was indeed confused because he was
>>> suggesting to delete them one by one.
>>>
>>> I need to read about the "lower_revs_limit". We never replicate this data.
>>>
>>>
>>> On Thu, Jun 14, 2012 at 3:08 PM, Tim Tisdall <tisdall@gmail.com> wrote:
>>>
>>>> I think he's suggesting avoiding compaction completely.  Just delete
>>>> the old DB when you've finished deleting all the records.
>>>>
>>>> On Thu, Jun 14, 2012 at 9:05 AM, Nicolas Peeters <nicolists@gmail.com>
>>>> wrote:
>>>> > Interesting suggestion. However, this would perhaps have the same effect
>>>> > (deleting/compacting the old DB is what makes the system slower)...?
>>>> >
>>>> > On Thu, Jun 14, 2012 at 2:54 PM, Robert Newson <rnewson@apache.org>
>>>> wrote:
>>>> >
>>>> >> Do you eventually delete every document you add?
>>>> >>
>>>> >> If so, consider using a rolling database scheme instead. At some
>>>> >> point, perhaps daily, start a new database and write new transaction
>>>> >> logs there. Continue deleting old logs from the previous database(s)
>>>> >> until they're empty (doc_count:0) and then delete the database.
>>>> >>
>>>> >> B.
>>>> >>
>>>> >> On 14 June 2012 13:44, Nicolas Peeters <nicolists@gmail.com>
wrote:
>>>> >> > I'd like some advice from the community regarding compaction.
>>>> >> >
>>>> >> > *Scenario:*
>>>> >> >
>>>> >> > We have a large-ish CouchDB database that is being used for
>>>> transactional
>>>> >> > logs (very write heavy). Once in a while, we delete some of
the
>>>> records
>>>> >> in
>>>> >> > large batches and we have scheduled compaction (not automatic
(yet))
>>>> >> every
>>>> >> > 12hours.
>>>> >> >
>>>> >> > From what I can see, the DB is being hammered significantly
every 12
>>>> >> hours
>>>> >> > and the compaction is taking 4 hours (with a size of 50-100GB
of log
>>>> >> data).
>>>> >> >
>>>> >> > *The problem:*
>>>> >> >
>>>> >> > The problem is that compaction takes a very long time and reduces
the
>>>> >> > performance of the stack. It seems that it's hard for the compaction
>>>> >> > process to "keep up" with the insertions, hence why it takes
so long.
>>>> >> Also,
>>>> >> > what I'm not sure is how "incremental" the compaction is...
>>>> >> >
>>>> >> >   1. In this case, would it make sense to run the compaction
more
>>>> often
>>>> >> >   (every 10 minutes); since we're write-heavy.
>>>> >> >      1. Should we just run more often? (so hopefully it
doesn't do
>>>> >> >      unnecessary work too often). Actually, in our case,
we should
>>>> >> probably
>>>> >> >      never have automatic compaction if there has been no
>>>> "termination".
>>>> >> >      2. Or actually only once in a while? (bigger batch,
but less
>>>> >> >      "useless" overhead)
>>>> >> >      3. Or should we just wait that a given size (which
is the
>>>> problem
>>>> >> >      really) is hit and use the auto compaction (in CouchDB
1.2.0)
>>>> for
>>>> >> this?
>>>> >> >   2. In CouchDB 1.2.0 there's a new feature: auto
>>>> >> > compaction<
>>>> >> http://wiki.apache.org/couchdb/Compaction#Automatic_Compaction>
>>>> >> > which
>>>> >> >   may be useful for us. There's the "strict_window" feature
to give
>>>> a max
>>>> >> >   amount of time to compact and cancel the compaction after
that (in
>>>> >> order
>>>> >> >   not to have it running for 4h+…). I'm wondering what the
impact of
>>>> >> that is
>>>> >> >   on the long run. What if the compaction cannot be completed
in that
>>>> >> window?
>>>> >> >
>>>> >> > Thanks a lot!
>>>> >> >
>>>> >> > Nicolas
>>>> >>
>>>>
>>>
>>>

Mime
View raw message