Re: BUG #14345: run multi-PG9.6 on One Host, hang when checkpoint

On Thu, Sep 29, 2016 at 12:35 AM, <digoal(at)126(dot)com> wrote:

> encountered the problem of Hang checkpoint.

> vm.overcommit_ratio = 90
> vm.swappiness = 0

If you change vm.swappiness to 10 can you still see the problem?

The reason I ask is that vm.overcommit_ratio sets the maximum RAM
that can be allocated to swap size plus the specified percentage of
actual RAM (in your case 90% of RAM in addition to allocated swap
space). On the other hand, depending on kernel version,
vm.swappiness = 0 may be telling the OS not to swap anything out,
even if it is never accessed (i.e., it should prefer to throw away
even a very recently referenced page in the cache). This
combination of settings seems somewhat likely to cause problems.

While "conventional wisdom" is that setting vm.swappiness = 0
improves performance, the few benchmarks I have seen related to
that show otherwise.

--
Kevin Grittner
EDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company