I maintain an ancient Oracle Reports system, which does a peculiar FTP gyration that recently started giving us errors.
Here's the scenario: We have a database that powers a farm of six Oracle Reports servers. Some of the reports we generate are tilde-delimited text files that have to be FTP'd into a mainframe computer. (Don't ask — it's an ancient system and it's not going to be changed anytime soon.)
This was all written before the feature was introduced in the Oracle Reports server that supports FTP as a target. In other words, it was written before we could FTP directly from the Reports server into the mainframe. So when the database sends a URL to one of the Reports servers, it waits and reads back in the resulting report text file. This gets saved as a blob in the database, and the database periodically exports the blobs into the local file system and runs an external Java FTP process to push those files into the right location on the mainframe.
Things started blowing up recently when the 10g server tried to save the incoming text file as a blob in the database. There's no way — at least no way that I know — to stream the incoming file into the database. It has to wait, read in the entire text file from the Reports server, and then save that entire chunk into the database, which means that the database has to allocate temporary storage somewhere to hold the text file until it can be written out.
These text files are not small — some of them have grown into the hundred-megabyte range. These six files are scheduled very early in the morning, so there should not be that much traffic on the database server I'm using; besides, the database server has 8 GB of RAM and only runs the database. There is plenty of capacity to temporarily hold these reports.
We recently started seeing a bunch of ORA-04030 errors in our application error log. The error text would say something like "out of process memory when trying to allocate 16396 bytes."
Our first thought was to check RAM usage, which we did, and everything looked fine. The database had way more headroom than it needed to allocate RAM for these files. Our DBA opened up a support ticket with Oracle and, after a bit if investigating, it turns out we were running low on swap space for the database. We had a couple GB of free disk space but apparently that wasn't enough for the hungry database server. Luckily, it's not a real disk — it's virtual running on a big EMC disk farm. We were able to fairly easily get it expanded to give more room for the database.
I'm still not clear on why the database didn't warn us specifically about the swap space issue. Why give this general out-of-memory error, which mislead us into thinking RAM was the issue? If the database knew it was swap space at issue instead of RAM, it should have been indicated in the error text.