you need to include in your QUERY_STRING=MAP=....&
it is probably hard coded in the fcgi config.
-Steve W
On 7/22/2020 7:15 PM, English Paul wrote:
So you have a complex historical "mess" and its not clear where the
performance issue is. So you need to divide the problem into small
problems that you can verify are or are not contributing. I would
start with something like this:
Thank you – I would not have thought to try it outside of CGI entirely!
Take one slow image request and try that as cgi or cli and not fcgi
and turn on debugging.
- copy and rename you mapfile so it doesn't mess with the production
requests
Not a major worry in this case – I’m working in an entirely dev
environment. I did make backup copies though!
- turn on the debugging and send it to stderr in the debug mapfile
- you can manually run that image request from the commandline like:
if mapserv is not in your path you might need to find it and your the
path to it below
mapserv -nh QUERY_STRING="everything after the ? in the original
query" >junk.png 2>error.txt
-nh suppresses headers from being output before the image data
error.txt will be stderr output and should contain the debug messages
I couldn’t quite get there – which this is what I ended up running:
# /usr/libexec/mapserv -nh
QUERY_STRING="FORMAT=image%2Fpng&LAYERS=winter1km_5min&TRANSPARENT=TRUE&SERVICE=WMS&VERSION=1.1.1&REQUEST=GetMap&STYLES=&TIME=2020-07-22T22%3A30%3A00Z&SRS=EPSG%3A900913&BBOX=-11584184.507886,4070118.8849183,-11271098.44003,4383204.9527744&WIDTH=256&HEIGHT=256"
> junk.png 2>error.txt
I first tried it with our current map file(s), and then with
MS_ERRORFILE set to stderr and DEBUG set to 5, in both cases, I got an
empty error.txt, and the following in junk.png:
Content-type: text/html
<HTML>
<HEAD><TITLE>MapServer Message</TITLE></HEAD>
<!-- MapServer version 6.0.1 OUTPUT=GIF OUTPUT=PNG OUTPUT=JPEG
OUTPUT=KML SUPPORTS=PROJ SUPPORTS=AGG SUPPORTS=CAIRO SUPPORTS=FREETYPE
SUPPORTS=ICONV SUPPORTS=FRIBIDI SUPPORTS=WMS_SERVER
SUPPORTS=WMS_CLIENT SUPPORTS=WFS_SERVER SUPPORTS=WFS_CLIENT
SUPPORTS=WCS_SERVER SU
PPORTS=SOS_SERVER SUPPORTS=FASTCGI SUPPORTS=THREADS SUPPORTS=GEOS
INPUT=POSTGIS INPUT=OGR INPUT=GDAL INPUT=SHAPEFILE -->
<BODY BGCOLOR="#FFFFFF">
loadMap(): Web application error. CGI variable "map" is not set.
</BODY></HTML>
I noticed that if I ran it with just -nh, I get the following:
#/usr/libexec/mapserv -nh
This script can only be used to decode form results and
should be initiated as a CGI process via a httpd server.
So maybe this older version just really doesn’t want to be run on the
CLI? Or maybe I’m messing up the QUERY_STRING, or need to set the CGI
variable to something as the junk.png output suggests?
Thanks again and thanks SO MUCH for the super quick reply!!
Paul
On 7/22/2020 1:47 PM, English Paul wrote:
Hi,
Newbie here, just got a work assignment to look into some
performance issues with mapserver-6.0.1-3_0.el6.x86_64 –
specifically, at one time, it rendered radar images very fast,
then it degraded and seemed to consume a lot more CPU. So – the
EC2 instance side was upgraded significantly – and it still
performs badly and uses a lot of CPU. It also seems to be getting
slowly worse over time (days/months, not seconds/minutes). I asked
this on IRC, but it looks like email might be a better route.
During all of this, the same mapserver instance renders
satellite images quickly. These seem to be a similar, or in some
cases larger size png to start with, rendered onto the same final
map/size.
So – the obvious answer is that it isn’t using the CPU to
render/re-render, but rather spending it on something else – I/O
most likely – eg: a network request, disk I/O, SQL query?
The previous person working on it tried turning on debug at
various levels – but unfortunately that made it even slower,
making it tricky to answer “what is making it slow when debug is
turned off?”
My first instinct was to try an strace and nothing was obvious.
Next up – a flame graph from strace, and/or trying dtrace – but my
understanding is that dtrace is a little weak on
RHEL/CentOS/Amazon Linux 6.0 **and** I’m not particularly good at
that. Also, we’re using fcgi, so attaching to the correct process
is a bit tricky.
My next instinct was to look at release notes and see if the
current stable has anything fixes/improvements that directly
address this – there aren’t any that are obvious to my eyes, but
you developers have been busy! So many things! Including some
performance fixes and one “significant” performance fix.
Current config file:
AddHandler fcgid-script fcgi
FcgidIPCDir /var/run/mod_fcgid
FcgidProcessTableFile /var/run/mod_fcgid/fcgid_shm
FcgidMaxProcesses 10
FcgidMaxProcessesPerClass 10
FcgidMaxRequestInMem 196608
FcgidInitialEnv PROJ_LIB /usr/share/proj
FcgidInitialEnv LD_LIBRARY_PATH "/usr/local/lib:/usr/pgsql-9.1/lib"
So – suggestions for my next move? I currently plan to take a
quick swing at building 7.6 for RHEL 6.0, knowing there might be
old libraries and whatnot that make that a non-starter. Of course
– we’ve got other infra running on this same instance, so
upgrading everything is a much bigger task.
Strace flame graph?
Stretch and try dtrace?
A better way to use debug?
Something else I’m missing – eg: differences between the image
types that make them perform so differently?
Thanks,
Paul
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