couchdb-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Debasish Ghosh <ghosh.debas...@gmail.com>
Subject Re: Query server perfromance issues ..
Date Mon, 21 Sep 2009 07:19:39 GMT
It's in fact referring to a reader that wraps System.in.
readLine returns null on end of file, but the earlier version of the
snapshot handles it and does not close the query server process. While the
new server seems to get throttled in the while loop. In fact this is one
difference that I forgot to mention. In the earlier version the query server
does not close, while in the new version it gets closed and restarted for
every view operation. Maybe it's getting closed because of the null. I can
figure that out from the logs. Is this an intentional change in
implementation ?

Robert -

I am not ignoring null. The while loop is very similar to what u mention. I
switched to the while true version just to log and see if nulls are getting
returned.

Thanks.
- Debasish

On Mon, Sep 21, 2009 at 3:53 AM, Paul Davis <paul.joseph.davis@gmail.com>wrote:

> On Sun, Sep 20, 2009 at 1:34 AM, Debasish Ghosh
> <ghosh.debasish@gmail.com> wrote:
> > Chris -
> > In my query server code, I logged everything that gets exchanged between
> the
> > couchdb server process and the query server. The difference that I
> noticed
> > with the new changes are that the couchdb server sends a huge number of
> null
> > strings to the view server which chokes the latter. In the snippet that I
> > wrote before ..
> >
> > while (true) {
> >>> >  s = inputstreamreader.readLine  // this reads from stdin
> >>> >  if (s == null) // ignore
> >>> >  else
> >>> >  toJson(s) match {
> >>> >    //.. process reset, add_fun etc.
> >>> >  }
> >>> > }
> >
>
> Does inputstreamreader.readLine refer to this function:
>
>
> http://java.sun.com/j2se/1.5.0/docs/api/java/io/BufferedReader.html#readLine%28%29
>
> If so, and that's returning null, then is it signaling that CouchDB
> has tried to close the input stream?
>
> Paul
>
> > I put logs in the true branch of if (s == null) and moments later I found
> a
> > log created of size 10 MB where the view server gets null strings from
> > stdin. This may give some clues towards the problem.
> >
> > Hope this helps.
> > - Debasish
> >
> >
> >
> >
> >
> > On Sun, Sep 20, 2009 at 10:56 AM, Chris Anderson <jchris@apache.org>
> wrote:
> >
> >> On Sat, Sep 19, 2009 at 10:09 PM, Debasish Ghosh
> >> <ghosh.debasish@gmail.com> wrote:
> >> > Yes, actually the reason I brought it up is that the same query server
> >> runs
> >> > fine with the earlier version, while it stumbles with the changes
> >> > incorporated later. Actually there is a really really big difference
> in
> >> > performance which is primarily because of the timeouts. Thanks for
> >> deciding
> >> > to look into it. I will currently stick around with the April
> >> > snapshot.Please post your findings on this list - I will be happy to
> >> upgrade
> >> > to the latest.
> >> > Thanks.
> >> > - Debasish
> >>
> >> I think what we'll need is a way to get visibility between the beam
> >> process and the query server. this could be accomplished with a simple
> >> log wrapper around the query server, logging both stdin and stdout to
> >> individual files.
> >>
> >> I like the idea of implementing it as a wrapper because then we can
> >> wrap it around the scala as well as the JS query server (and other
> >> languages), and get complete transparency into what's going over the
> >> wire.
> >>
> >> This is definitely turning into dev@ territory so I'm moving this
> thread
> >> there.
> >>
> >> Chris
> >>
> >> >
> >> > On Sun, Sep 20, 2009 at 3:41 AM, Chris Anderson <jchris@apache.org>
> >> wrote:
> >> >
> >> >> On Sat, Sep 19, 2009 at 11:40 AM, Debasish Ghosh
> >> >> <ghosh.debasish@gmail.com> wrote:
> >> >> > Here are some additional behavior changes that I am noticing
> between
> >> the
> >> >> 2
> >> >> > versions ..
> >> >>
> >> >> The other big change is in couch_os_process, the addition of
> >> >> couchspawnkillable - maybe this is acting up on your system.
> >> >>
> >> >> Partially I'm interested in getting to the bottom of this because it
> >> >> could be that it's inefficient with the JS query server, but not
> >> >> causing errors, and we just haven't noticed.
> >> >>
> >> >> > In the newer version, I notice lots of null strings being sent
> >> >> continuously
> >> >> > from the couchdb server to the view server. My view server loop
> looks
> >> >> like
> >> >> > the following :-
> >> >> >
> >> >> > while (true) {
> >> >> >  s = inputstreamreader.readLine
> >> >> >  toJson(s) match {
> >> >> >    //.. process reset, add_fun etc.
> >> >> >  }
> >> >> > }
> >> >> >
> >> >> > With the new version, I find lots of null strings coming in to
"s",
> >> which
> >> >> > makes me include something like the following ..
> >> >> >
> >> >> > while (true) {
> >> >> >  s = inputstreamreader.readLine
> >> >> >  if (s == null) // ignore
> >> >> >  else
> >> >> >  toJson(s) match {
> >> >> >    //.. process reset, add_fun etc.
> >> >> >  }
> >> >> > }
> >> >> >
> >> >> > And this null business is really huge. Has there been any change
in
> >> the
> >> >> > protocol between the couchdb server and the view server ? I suspect
> >> that
> >> >> > these null exchanges are taking up lots of cycles which result
in
> >> process
> >> >> > time out in the new version. I do not get this null stuff with
the
> >> older
> >> >> > version. Is there any chance of such happening with the changes
> that
> >> have
> >> >> > been done in couch_query_servers.erl ?
> >> >> >
> >> >> > Thanks.
> >> >> > - Debasish
> >> >> >
> >> >> >
> >> >> > On Sat, Sep 19, 2009 at 11:34 PM, Debasish Ghosh
> >> >> > <ghosh.debasish@gmail.com>wrote:
> >> >> >
> >> >> >> actually my ["reset"] is not expensive at all .. it just has
a
> >> >> array.clear
> >> >> >> kind of call.
> >> >> >> Just another observation when I run in debug mode I find that
> there
> >> are
> >> >> >> quite a few cases of OS Process Error {os_process_error, "OS
> process
> >> >> timed
> >> >> >> out."} being recorded in couch.log. I do not get this when
I am
> >> running
> >> >> the
> >> >> >> earlier version. However no unnatural things appear in
> >> couchdb.stderr.
> >> >> My
> >> >> >> current setting of os_process_timeout is 20000 .. I guess
that's
> 20
> >> secs
> >> >> ..
> >> >> >>
> >> >> >> Thanks.
> >> >> >> - Debasish
> >> >> >>
> >> >> >>
> >> >> >> On Sat, Sep 19, 2009 at 10:27 PM, Chris Anderson <
> jchris@apache.org
> >> >> >wrote:
> >> >> >>
> >> >> >>> On Sat, Sep 19, 2009 at 5:13 AM, Debasish Ghosh
> >> >> >>> <ghosh.debasish@gmail.com> wrote:
> >> >> >>> > Hi -
> >> >> >>> > As I have mentioned previously I have been working
on a Scala
> >> driver
> >> >> for
> >> >> >>> > CouchDB, which also includes a Query Server. I was
working with
> an
> >> >> April
> >> >> >>> > snapshot of 2009/04/23. This worked fine for all
the views and
> >> >> >>> validations
> >> >> >>> > that I have written.Things were running fine and
I could write
> >> >> >>> map/reduce
> >> >> >>> > and validation functions in Scala.
> >> >> >>> > Recently I tried to upgrade to trunk. Suddenly the
views and
> >> >> validations
> >> >> >>> > became very very slow. After some fact finding, I
tried to poke
> >> into
> >> >> *
> >> >> >>> > couch_query_servers.erl*, since that seemed to be
the obvious
> area
> >> to
> >> >> >>> look
> >> >> >>> > into. I may be worng though, but it was a blind guess.
> >> >> >>> > I noticed that previously I was working with *revision
749852*
> of
> >> the
> >> >> >>> file,
> >> >> >>> > which delivered the goods for me. Then when I faced
problems
> with
> >> the
> >> >> >>> trunk,
> >> >> >>> > I started doing a git reset to earlier versions of
this file.
> Now
> >> I
> >> >> find
> >> >> >>> > that it looks like the performance problem starts
from
> *revision
> >> >> 780165*
> >> >> >>> of
> >> >> >>> > this file. Have a look at
> >> >> >>> >
> >> >> >>>
> >> >>
> >>
> http://svn.apache.org/viewvc/couchdb/trunk/src/couchdb/couch_query_servers.erl?r1=780165&r2=749852&diff_format=hfor
> >> >> >>> > the difference. Looks like there have been some major
changes.
> I
> >> am
> >> >> >>> > just
> >> >> >>> > wondering if this change has anything to do with
the
> performance
> >> >> issue.
> >> >> >>> >
> >> >> >>>
> >> >> >>> A quick scan of that diff suggests that the only real
behavior
> >> change
> >> >> >>> that should effect you is the ["reset"] call for recycled
> processes.
> >> >> >>> Maybe reset is expensive in your implementation?
> >> >> >>>
> >> >> >>> BTW, have you tried running:
> >> >> >>>
> >> >> >>> spec test/query_server_spec.rb -f specdoc --color
> >> >> >>>
> >> >> >>> It should be simple to extend that test suite to test
your scala
> >> >> >>> server. If there are patches we can make to make it easier
to
> >> >> >>> integrate outside projects with the query server test
suite, I'm
> >> happy
> >> >> >>> to help there as well.
> >> >> >>>
> >> >> >>> > Any help, pointer will be appreciated.
> >> >> >>> >
> >> >> >>> > Thanks.
> >> >> >>> > - Debasish
> >> >> >>> >
> >> >> >>>
> >> >> >>>
> >> >> >>>
> >> >> >>> --
> >> >> >>> Chris Anderson
> >> >> >>> http://jchrisa.net
> >> >> >>> http://couch.io
> >> >> >>>
> >> >> >>
> >> >> >>
> >> >> >
> >> >>
> >> >>
> >> >>
> >> >> --
> >> >> Chris Anderson
> >> >> http://jchrisa.net
> >> >> http://couch.io
> >> >>
> >> >
> >>
> >>
> >>
> >> --
> >> Chris Anderson
> >> http://jchrisa.net
> >> http://couch.io
> >>
> >
>

Mime
  • Unnamed multipart/alternative (inline, None, 0 bytes)
View raw message