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

Filtering in the APEX Interactive Grid

By
Remember Oracle Forms? One of the nice features of Forms was the use of GLOBAL items. More or less comparable to Application Items in APEX. These GLOBALS where often used to pre-query data. For example you queried Employee 200 in Form A, then opened Form B and on opening that Form the Employee field is filled with that (GLOBAL) value of 200 and the query was executed. So without additional keys strokes or entering data, when switching to another Form a user would immediately see the data in the same context. And they loved that. In APEX you can create a similar experience using Application Items (or an Item on the Global Page) for Classic Reports (by setting a Default Value to a Search Item) and Interactive Reports (using the  APEX_IR.ADD_FILTER  procedure). But what about the Interactive Grid? There is no APEX_IG package ... so the first thing we have to figure out is how can we set a filter programmatically? Start with creating an Interactive Grid based upon the good o...
1 comment
Read more

apex_application.g_f0x array processing in Oracle 12

By
If you created your own "updatable reports" or your custom version of tabular forms in Oracle Application Express, you'll end up with a query that looks similar to this one: then you disable the " Escape special characters " property and the result is an updatable multirecord form. That was easy, right? But now we need to process the changes in the Ename column when the form is submitted, but only if the checkbox is checked. All the columns are submitted as separated arrays, named apex_application.g_f0x - where the "x" is the value of the "p_idx" parameter you specified in the apex_item calls. So we have apex_application.g_f01, g_f02 and g_f03. But then you discover APEX has the oddity that the "checkbox" array only contains values for the checked rows. Thus if you just check "Jones", the length of g_f02 is 1 and it contains only the empno of Jones - while the other two arrays will contain all (14) rows. So for ...
Post a Comment
Read more

Stop using validations for checking constraints !

By
 If you run your APEX application - like a Form based on the EMP table - and test if you can change the value of Department to something else then the standard values of 10, 20, 30 or 40, you'll get a nice error message like this: But it isn't really nice, is it? So what do a lot of developers do? They create a validation (just) in order to show a nicer, better worded, error message like "This is not a valid department".  And what you then just did is writing code twice : Once in the database as a (foreign key) check constraint and once as a sql statement in your validation. And we all know : writing code twice is usually not a good idea - and executing the same query twice is not enhancing your performance! So how can we transform that ugly error message into something nice? By combining two APEX features: the Error Handling Function and the Text Messages! Start with copying the example of an Error Handling Function from the APEX documentation. Create this function ...
Post a Comment
Read more