Antwort: Re: [UMN_MAPSERVER-USERS] Antwort: Re: [UMN_MAPSERVER-USERS] Bug in msCopy

[Benedikt Rothe]

Thank's Umberto. I did not know -Xloggc before.

As far as I understood -Xloggc measures the memory allocated by the JVM.
And this is the kind of memory which is not hazardous ...

Anyway I will look in this direction...

Benedikt

Umberto Nicoletti <umberto.nicoletti at gmail.com> schrieb am 29.06.2005 
12:10:03:

> On 6/29/05, Benedikt Rothe <umn-ms at hydrotec.de> wrote:
> > 
> > Hello Umberto 
> > 
> > Thank you for yout hint's! 
> > 
> > You are right: One should be cautios. But for the moment I have the
> > impression 
> > that we seeme to have found a way, which don't raise obvious errors in 
the
> > first 
> > moment :-) 
> > 
> > After the mentioned changes in mapcopy.c the approache 
> > (TomCat/MapScript/Connection-Pooling/MapCloning) seeme to 
> > work for us. (Working with Version 4.6) 
> > 
> > But: 
> > - We do need some more stress-testing.(We already made automated 
> >   http-requests from a Java-Programs. But this was definitly not 
enough and 
> >   not "nasty" enough!) 
> 
> jmeter is an excellent tool for stress/load testing (
> jakarta.apache.org/jmeter/ )
> 
> > - New problems could raise, if more or other features from
> > mapserver/mapscript 
> >   are used then we actualy do. 
> > - Memory footprint of the running-tomcat has to be watched!. What 
about the
> > size 
> >    of the application after 100, 500, 600, 800 ... requests? (I'm not 
quite
> > shure how to do this!
> 
> Use the -Xloggc:/tmp/gc.log to java when starting tomcat and then run
> the stress tests. You should be able to see that if memory get
> correctly garbage collected the avail mem is almost always equal to a
> certain initial size.
> Warning: this is not 100% error proof, but it should be start. try 
googling...
> 
> Ciao,
> Umberto
> 
> >    Watching Java-Programs is difficult because of garbage-collections 
...) 
> > 
> > Greetings 
> > Benedikt 
> > 
> > Umberto Nicoletti <umberto.nicoletti at gmail.com> schrieb am 29.06.2005
> > 11:03:46:
> > 
> > 
> >  > On 6/29/05, Benedikt Rothe <umn-ms at hydrotec.de> wrote:
> >  > > 
> >  > > Dear List 
> >  > > 
> >  > > We are using MapScript/Tomcat/Java/OracleSpatial. 
> >  > > 
> >  > > We use mapObj.mapClone() to get a fresh mapObject 
> >  > > in each request without reading the Mapfile. 
> >  > 
> >  > Benedikt,
> >  > I would not do that (tm). In my apps I recreate a fresh mapObj with
> >  > each request  as the overhead is mininum and the benefits high (so
> >  > that the ratio is in favor of this approach).
> >  > Besides this is the only known method to work (as far as I know) 
and
> >  > this stems from the fact that mapserver was in the beginning (and
> >  > still is, with improvements) a CGI. As you might know cgis are
> >  > processes that are created by the web server to serve a single 
request
> >  > and then exit, so memory cleanup and thread safety are non-issues 
for
> >  > them.
> >  > Even in php mapscript php must be used as a cgi (instead of a DSO) 
to
> >  > make sure that it works.
> >  > 
> >  > > 
> >  > > We detected problems after we activated Connection-Pooling: 
> >  > > Tomcat crashed in mapObj.delete() 
> >  > >
> >  > 
> >  > I would not use connection pooling just because it will not work
> >  > reliably with Java Servlets for the reasons explained above.
> >  > 
> >  > This matter (connection pooling and map cloning) surely requires
> >  > deeper investigation, one of the developers coul step in to give 
his
> >  > opinion on my statements (which I would sincerely hope were false, 
but
> >  > fear not). Btw, I seem to recall that the above issues (long lived
> >  > instance against per request instance)  were already discussed on 
the
> >  > list before.
> >  > 
> >  > Best regards,
> >  > Umberto
> >  > 
> >  > > Hole thing turned out to be a bug in mapcopy.c where 
> >  > > the joins are copied: 
> >  > > -------------------- 
> >  > > MS_COPYSTELEM(numjoins); 
> >  > > 
> >  > > for (i = 0; i < dst->numprocessing; i++) { 
> >  > >    return_value = msCopyJoin(&(dst->joins[i]), &(src->joins[i])); 

> >  > > -------------------- 
> >  > > 
> >  > > This must be changed to 
> >  > > -------------------- 
> >  > > MS_COPYSTELEM(numjoins); 
> >  > > 
> >  > > for (i = 0; i < dst->numjoins; i++) { 
> >  > >    return_value = msCopyJoin(&(dst->joins[i]), &(src->joins[i])); 

> >  > > -------------------- 
> >  > > 
> >  > > There is some other code in mapobject.c, wich didn't 
> >  > > raise any problems for us, but from wich I do think 
> >  > > that array-allocs are missing. 
> >  > > I watched the code an *think* these are are not allocated 
> >  > > anywhere. I hope, there is no misleading hint: 
> >  > > 
> >  > >  ----------------------------
> >  > >  // I do think, that dst->point is not allocated.
> >  > >  // code seems to be unused (?)
> >  > >  dst->numpoints = src->numpoints;
> >  > >  for (i = 0; i < dst->numpoints; i++) {
> >  > >   MS_COPYPOINT(&(dst->point[i]), &(src->point[i]));
> >  > >  }
> >  > >  ----------------------------
> >  > >  // I do think, that dst->items and dst->values is
> >  > >  // not allocated
> >  > >  MS_COPYSTELEM(numitems);
> >  > >  for (i = 0; i < dst->numitems; i++) {
> >  > >   MS_COPYSTRING(dst->items[i], src->items[i]);
> >  > >   MS_COPYSTRING(dst->values[i], src->values[i]);
> >  > >  }
> >  > > 
> >  > >  -----------------------------
> >  > >  // I'm quite shure, that dst->items is not allocated
> >  > >  MS_COPYSTELEM(numitems);
> >  > > 
> >  > >  for (i = 0; i < dst->numitems; i++) {
> >  > >   MS_COPYSTRING(dst->items[i], src->items[i]);
> >  > >  }
> >  > > 
> >  > > I hope this is helpful. Greetings 
> >  > > Benedikt Rothe
> >
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