Hanging process when inserting in xmltable

I'm using Oracle Database 12c (12.1.0.1.0 64Bit). Some time ago I wrote a piece of software in pl/sql to import several XML-files. This seemed to work very well, but then some problems occurred. Some files are 5 to 25 MB in size, so it takes one or two minutes to import them. But for some files the import never ends and the importing process even can't be stopped, I have to restart the server to get rid of it.

I traced the problem to the following row:

INSERT INTO SB_BUFFER_XML VALUES (XMLType(bfilename('XMLDATA', '840.xml'), nls_charset_id('AL32UTF8')));

The table SB_BUFFER_XML is of type xmltable and XMLDATA points to a local directoy. The command never finishes with the file 840.xml. But it finishes with the file 613.xml. Both are similar in size, the 613.xml is even bigger:

840.xml: 6.329 KB
613.xml: 6.905 KB

So I started to compare both files looking for the problem:

both files are UTF-8 without BOM
both contain the same structure, but different data
the xml-syntax check finished successful
even in a hex editor both files start and finish with the same characters (so theres no hidden BOM or something)
both files were created in the same system in the same version

So I simply started to delete content from 840.xml to reduce the complexity and I saw that it doesn't matter what I delete. As soon as I delete a specific amount of data, even if it is a comment, the import of this file works flawless.

The strange thing is that I already did import xml-files with the same structure from the same system with a file size of over 20 MB.

Do you have any idea what could cause this problem or what I could check next?

Solution

Oracle could reproduce our problem and pointed us to the following bug:

Bug 22843562 - IMPORT OF A XML FILE WITH A COMMENT AT THE END FAILS WITH ORA-27163

This bug is fixed in 12.2. In 12.1 you can try this workaround to activate the old parser:

ALTER SESSION SET EVENTS '31156 trace name context forever, level 0x400';

While the bug title didn't describe our problem, the workaround worked for us nevertheless.