Giles Lean ha scritto:
Silvio Brandani <silvio.brand...@tech.sdb.it> wrote:
yes the server is dedicated to PostgreSQL.
Could be a bug of PostgreSQL the fact that the system went Out of
Memory?? Wath can be the cause of it?
Regards,
Silvio
The out of memory killer is a totally bogus misfeature of
Linux. At least these days they let you turn it off, and
everyone should turn it off _and_ should bug their OS vendor
to request that they ship their distribution with memory
overcommit and the out of memory killer disabled.
The "out of memory" killer only exists because Linux by
default will allow more memory to be allocated than exists in
the system. This is called "memory overcommit" and is kown in
operating system circles (outside of Linux) to be a bad thing.
The rationale for memory overcommit being a bad thing is that
if your OS doesn't allow allocation of more memory than there
is in the system, then applications are forced to deal with
memory requests that fail, instead of seeing those requests
"succeed" and being killed some random time later.
Allowing more memory to be "allocated" than exists in the
machine is only useful in two circumstances that I know of,
and neither apply to a dedicated PostgreSQL system, running
Linux or not:
1. When badly written applications allocate far more memory
than they use. PostgreSQL isn't like that.
The technically correct solution is to fix the
applications; allowing memory overcommit is a dangerous
workaround that _will_ cause problems.
2. When very large processes need to fork (e.g. a scientific
numerical analysis program using most of physical memory)
might want to fork to send an email notification or
something similar).
The technically correct solution is to use vfork().
I won't make myself popular with the Linux zealots, but memory
overcommit should just be removed from Linux. It does way more
harm than good on any operating system I've ever seen it used
on, and the problems it has caused just on Linux are legion.
The only OS that had _any_ excuse for memory overcommit I've
seen was one that lacked a vfork() system call; they added
that call and the justification for memory overcommit went
away.
Regards,
Giles
Thanks a lot,
I' m going to disable the memory killer, moreover I have run the
Operative System watcher scripts to monitor the undergoing activity in
case it happens again.
Best Regards,
Silvio Brandani
--
Silvio Brandani
Infrastructure Administrator
SDB Information Technology
Phone: +39.055.3811222
Fax: +39.055.5201119
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