Skip to main content

Help! APEX is blowing up our memory!

By
That's the message I received from a DBA friend who ran into this problem at her customer site. What really happened was that a couple of times a week one of the APEX processes was killed by the operating system due to reaching the limit of 16Gb memory. 16Gb!
And this resulted in an ORA-04030 message in the Oracle Database.
So I went to that client site and we dove into the database log files, the APEX logging, the access log files and the error log files of the web server. Every time we noticed calls of WWW_FLOW_FILE_MGR.GET_FILE that seemed to be the problem. But the application wasn't huge, just 25 pages. Nothing complex, all pretty straight forward. So we started to look for the origin of those calls.
Just like in a lot of applications, this application also had a few images on the top of the screen (like Home, Logout, etc.). Just four or five on every page. However, these images were stored inside the APEX Repository, using the #WORKSPACE_IMAGES# substitution string. And that results in a call to WWW_FLOW_FILE_MGR.GET_FILE for every image. So that's five requests for every page, while it could - and should - be only one. And four executions of that procedure every time, while it could - and should - be zero. So I advised to move these images to the web server, so they can be cached and wouldn't result in hitting the database anymore.
But when this would be the cause of the problem, it made sense it would occur on peak times. But the problem didn't occur on peak times. The last one was that same morning around 4:30AM.
So we dove further and then we discovered that quite a few of the select statements in the application used #WORKSPACE_IMAGES# as well! So the procedure would be executed for every row returned by the select statement. So in some particular cases - just happening three times a week or so - the query would return 10,000 of rows. Or even millions. So the procedure would be executed that often. And the best thing is: the image that the select was trying to retrieve ... didn't even exists! So millions of calls to the database to retrieve ... nothing!
So changing the select statements and moving all images to the web server will reduce the number of calls to that procedure from millions (or 100 of millions) times a week to ... zero (?).
And the chances are the memory problem is gone to.

So when you run into these kind of problems were APEX seems to consume a lot of memory - or CPU for that matter - take a very good look to your own code first. The chances are that the resource consumption is not because APEX is misbehaving, but your code isn't optimal....

Comments

Post a Comment

Popular posts from this blog

How to create neatly formatted Excel documents using PL/SQL?

By
If there is a requirement to produce output from an application into Excel, you would probably create a CSV (Comma Separated File) with the data and start Excel to show the data - at least that's what I did...until now. The drawback of this solution is that you could only produce data and no nice layout. But Excel is also capable of opening HTML-files and using this you could create Excel files with data and magnificent layout! Let me give an example: 1. Create a procedure to show the data in formatted in an HTML table. CREATE OR REPLACE PROCEDURE display_emp_list IS v_emp_count NUMBER(5); v_empno NUMBER(8); v_ename VARCHAR2(50); v_job emp.job%TYPE; v_sal emp.sal%TYPE; v_bg_color VARCHAR2(10) := ''; CURSOR c_emp IS SELECT empno, initcap(ename), job, sal FROM emp ORDER BY ename; BEGIN SELECT COUNT(*) INTO v_emp_count FROM emp; owa_util.mime_header('application/ms-excel', FALSE); htp.p('Content...
21 comments
Read more

Refresh selected row(s) in an Interactive Grid

By
In my previous post I blogged about pushing changed rows from the dabatase into an Interactive Grid . The use case I'll cover right here is probably more common - and therefore more useful! Until we had the IG, we showed the data in a report (Interactive or Classic). Changes to the data where made by popping up a form page, making changes, saving and refreshing the report upon closing the dialog. Or by clicking an icon / button / link in your report that makes some changes to the data (like changing a status) and ... refresh the report.  That all works fine, but the downsides are: The whole dataset is returned from the server to the client - again and again. And if your pagination size is large, that does lead to more and more network traffic, more interpretation by the browser and more waiting time for the end user. The "current record" might be out of focus after the refresh, especially by larger pagination sizes, as the first rows will be shown. Or (even wors...
Post a Comment
Read more

APEX ReadOnly Pages - The easy way

By
If your Oracle APEX Application requires different types of access - full access or readonly - for different types of users, you can specify a Read Only Condition on Page level (or Region, Item, Button, etc.).  You can set an Authorization Scheme on Application level, so it'll be applied to all pages. So if you have an Authorization Scheme named 'User Can Access Page' defined by a PL/SQL function like this: return apex_authorization.user_can_access_page ( p_app_id  => :APP_ID , p_page_id => :APP_PAGE_ID , p_user    => :APP_USER );  then you can code all the logic in the database using the APEX Repository, your own tables or a combination to define whether a user has access to that page or not. But alas it is not possible to define something similar Application wide for a Read Only condition. You can specify an Authorization Scheme 'User has Read Only Access' using a similar signature as the one above and use that on each and e...
Post a Comment
Read more