I wonder if anybody could shred some light regarding the following problem:
A month ago I upgraded our Moodle production site to Moodle 2.6.5 which is a very solid a reliable version. Our site runs on a Windows Server 2008-IIS7 virtual machine. We use php 5.5.13 and I have configured opcache in php.ini by the book following the instructions in Moodle.org
The day before yesterday, I installed some Windows security updates in the virtual machine and I restarted windows. The free space in the hard disk that runs Windows is 45 GB and the used space is 55 GB. I reported this to the network technical but the free space is not a problem, apparently, and 45 GB is enough for keep running IIS7.
Yesterday, after the installation of the updates and after I restarted Windows, we started to experience very weird problems: Moodle did not upload the css elements with the frontpage (that is: the frontpage was uploaded without the css of our theme), the site was specially slow and if you click in a course or resource, the screen went black (although there were not error entries in the php error log file).
I looked at the entries in the php error log file for yesterday and this is what I found:
[26-Nov-2014 19:10:49 Asia/Kuwait] Cannot obtain session lock for sid: pdgev7ood0n3egu82sgh1u4m62
[26-Nov-2014 19:12:38 Asia/Kuwait] Cannot obtain session lock for sid: pdgev7ood0n3egu82sgh1u4m62
[26-Nov-2014 19:12:47 Asia/Kuwait] Cannot obtain session lock for sid: pdgev7ood0n3egu82sgh1u4m62
[26-Nov-2014 19:13:06 Asia/Kuwait] Cannot obtain session lock for sid: pdgev7ood0n3egu82sgh1u4m62
19:00 Kuwait time (where our server is hosted) corresponds to 4:00 UK time, when I restarted IIS logging into the Windows machine.
Restarting IIS seem to have sorted the problem so far, but I am very concerned that it may happen again.
Does anybody know what do the 'Cannot obtain session lock for sid:....' messages mean and this is a seriour error or not?
Thank you very much for your advice.