Zitat von Willy-Bas Loos <willybas@xxxxxxxxx>:
Hi, I have a problem with postgres in combination with openvz. My hot standby crashes on me when i give it a normal value for shared_buffers (4GB, which 25% of the memory in the container). When i tune down the shared_buffers, it works again. But of course this is far from desireable.
Have a look at the bean counters from OpenVZ. Some of them have dependencies to each other and can lead to unexpected out-of-memory condition inside the container. Check the logs for the reason PostgreSQL crashed, maybe it was the OOM killer.
Now, i've seen a couple more messages around the net about openVZ and postgres that weren't very encouraging: http://www.postgresql.org/message-id/CAHyXU0xa5EgvjeH=4vp-eZDJdS5kMQuiDivvTRLjY-uZ62Y44w@xxxxxxxxxxxxxx
This is about Postgres not able to read a block from a file, so it looks like a filesystem issue to me.
http://www.postgresql.org/message-id/23206.1254683408@xxxxxxxxxxxxx
This is about "hot" migration which is in general a dangerous task for databases. Obviously it doesn't work in this case. We also had no success some time ago trying "hot" migration with Oracle Databases on OpenVZ.
http://postgresql.1045698.n5.nabble.com/BUG-9721-Fatal-error-on-startup-no-free-slots-in-PMChildFlags-array-td5797390.html
This is also a related problem to the above. Freezing a running database (which is also done for migration) must be atomic, else the internal database states might get confused.
But i am in a position where we already have a pretty strong binding with openVZ. I also have a colleague that has been using openVZ and postgres on production for quite a while now, without any problems. And already 1 of our servers is running a production database in openVZ that is well used, without any trouble of this kind. Now, what i would like to know is: - is there clarity about what the issues are at all - is it just 1 problem (in openVZ) that make openVZ and postgres so poorly compatible? - how can i stay out of trouble (when using postgres inside openVZ) - who else has trouble with openVZ in combination with postgres, and what constitutes the trouble?
From my point of view your problem is not related to the URLs shown. You have to carefully check the Container settings and errors and avoid freezing/migrating the database container if possible.
In general there is no Problem with databases inside Containers but you have to carefully check the settings for the container in question and test the advanced features like hot migration if you really have to use them.
Regards Andreas
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