Performance impact on displaying images when tested with loadrunner

Question

Hi,
We have a page in the application that displays PDF images to the user.
The PDF's are stored on HP-UX file system and have the BFILE path
of the image stored along with other meta-data. The ave size of the PDF is around 250 kb.The images are displayed fine when the user wants to view the images.
The problem we have been facing is more related to performance.
When loadrunner tests were conducted to allow 75 users to concurrently
view the images, the CPU utilization shoots up to 100%.
All other resources such as memory, io are fine and the image display time is
within acceptable limits.
Are there any settings or configurations that can be done to bring done the CPU utilization totolerable limits. Also the box hosts other application which we fear might be impacted and henceit is very important for us to bring down the cpu utilization
The code to display the PDF is similar to the one in sample app
PROCEDURE DISPLAY_PDF_PRC (IMAGE_PATH_I IN BFILE)
IS
V_BLOB BLOB;
V_BFILE BFILE;
BEGIN
V_BFILE := IMAGE_PATH_I;
V_BLOB := EMPTY_BLOB();
DBMS_LOB.CREATETEMPORARY(V_BLOB, TRUE);
DBMS_LOB.FILEOPEN(V_BFILE,DBMS_LOB.FILE_READONLY);
DBMS_LOB.LOADFROMFILE(V_BLOB,V_BFILE,DBMS_LOB.GETLENGTH(V_BFILE));
DBMS_LOB.FILECLOSE(V_BFILE);
OWA_UTIL.MIME_HEADER('application/pdf', FALSE);
OWA_UTIL.HTTP_HEADER_CLOSE;
WPG_DOCLOAD.DOWNLOAD_FILE(V_BLOB);
DBMS_LOB.FREETEMPORARY(V_BLOB);
EXCEPTION
WHEN OTHERS THEN
Htp.Prn('No image found.');
END;
We first thought creating the temporary blob might be costly and modified the code to use lob locator.Still the CPU utilization was over 100%.
The next thing we tried was to eliminate the creation and usage of BLOBs altogether and directly render the images from the BFILE as mentioned in the code below and tried to use the browser caching also.
PROCEDURE DISPLAY_PDF_PRC (IMAGE_PATH_I IN BFILE)
IS
V_BFILE BFILE;
BEGIN
V_BFILE := IMAGE_PATH_I;
htp.p('Expires: ' || to_char(sysdate + 1/24, 'FMDy, DD Month YYYY HH24:MI:SS'));
OWA_UTIL.MIME_HEADER('application/pdf', FALSE);
OWA_UTIL.HTTP_HEADER_CLOSE;
WPG_DOCLOAD.DOWNLOAD_FILE(V_BFILE);
end;
Still the CPU utilization is over 100%.
So can you please point to any configurations that neeed to be done on Apache App server/DB server or any optimizations at the code level to restrict the CPU utilization.
Thanks in Advance
Rakesh

Answer 1

Typically, you do not refer to PDFs as images. Common image formats are .jpg, .gif, .png, .bmp, etc.
Can you store them directly on the file system and just reference their URLs instead of reading them out of the database? If so, this should all but eliminate the CPU load.
If you only have one database on this machine, you can use the database resource scheduler to throttle the CPU utilization of the sessions downloading images. If you have more than one db, then the Resource Manager is basically useless, which is one of the main reasons to only install one db per machine.
Another thought is to use a web cache instance in front of the HTTP Server if their are a lot of repeat views of the same PDFs. This way you cache the first view of the PDF on the web cache tier so subsequent requests don't go against the db.
Yet another option (though not out for HP-UX yet) is the 11g "Secure Files" option. I've done some informal testing on this last week and read performance was easily 3x faster than traditional LOBs. My tests weren't very scientific as I was using VMWare on a laptop which generally has very poor physical I/O performance. They claim reads performance is comparable to the Linux file system.
Tyler