Re: Out of memory in CIFS leads to database crash

Jeff Janes <jeff(dot)janes(at)gmail(dot)com> writes:
> On Tue, Jan 7, 2014 at 2:03 AM, Umesh Kirdat <umesh(dot)kirdat(at)yahoo(dot)com> wrote:
>> I wish to know why is the database crashing if the file open fails? Why
>> can't it handle it gracefully by rolling back the transaction?

> Based on the section of the log you are showing, it looks like it did just
> roll back the transaction. A crash should be showing you PANIC messages,
> not just ERROR. Is there more to the log than you are showing? If you are
> logging over CIFS as well, perhaps the PANIC messages are getting lost
> because they can't be logged.

We will PANIC on I/O failure involving the WAL log, but as you say, this
log extract isn't showing instances of that. I/O failures on ordinary
data files shouldn't result in a panic. (I'm not sure whether it'd be
practical to downgrade the panic for WAL write failures. Certainly, the
database won't be good for much if it can't commit transactions. A WAL
write failure also implies that data from transactions besides the one
doing the write may be in jeopardy, so just pretending that the system
as a whole can carry on doesn't sound all that safe.)

> I don't think that running with the data directory on CIFS is supported. I
> certainly wouldn't be brave enough to do that with data I care about.

You should certainly be keeping the WAL log on a trustworthy filesystem;
and frankly I'm not sure what the point is of using a database on
known-untrustworthy storage of any breed. We can't be more reliable
than the underlying storage is.

regards, tom lane