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From Robert Newson <robert.new...@gmail.com>
Subject Re: Query server perfromance issues ..
Date Mon, 21 Sep 2009 12:16:02 GMT
I claim you are ignoring null here because of your comment;

while (true) {
 s = inputstreamreader.readLine
 if (s == null) // ignore
 else
 toJson(s) match {
   //.. process reset, add_fun etc.
 }
}

When System.in is closed this loop will spin; readLine() will always
return null. Since System.in is only closed when the JVM is exiting,
it is never correct to ignore it and continue processing.

The loop I presented is not the same as yours as mine will correctly
exit on process termination.

readLine() *cannot* return null under any circumstance but the close
of the stream (couchdb cannot pass you null this way). System.in is
never closed unless the process itself is exiting, and it is never
reopened.

The mishandling of readLine() is probably hiding the real problem. I
would guess you pass invalid JSON to couchdb, or fail to return
anything at all, under some conditions. Couch then kills your view
server (and would then restart it). The view server, rather than
gracefully exiting when this happens, will simple spin, never exiting.

B.

On Mon, Sep 21, 2009 at 8:19 AM, Debasish Ghosh
<ghosh.debasish@gmail.com> wrote:
> 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
>> >>
>> >
>
>

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