Re: could not read block XXXXX in file "base/YYYYY/ZZZZZZ": read only 160 of 8192 bytes

>
> I wonder if you are oversubscribing your memory, and are getting weird
> errors when reading data into memory because the pages can't be
> reserved to do that.  What happens when you enable overcommit and
> attempt to start the server?
>
> merlin

In my first post I wrote: "I tried to set vm.overcommit_memory=2 and vm.overcommit_ratio=90 - no sense. Then I tried
vm.overcommit_memory=1- no sense." 
"No sense" means that server starts, works for about 3 hours, and then dies with signal 7 and almost all buffers
filled.Just as with vm.overcommit_memory=0. 
I copypasted vmstat log, that shows that there were 5Gb of free memory when postgresql died. In one of my experiments
postgresqlworked for about half an hour with 0k free memory (at least top and vmstat said so). Abscence of free memory
wascaused by the fact that replica had been down for 12 hours or so, and when started wal writer procees took much
resources.But it was woking! With no free memory. 
But this is not important. As I noticed the thing is not how much free memory I have. The thing is how shared buffers
arefilled. And shared buffers fillings makes sense only when they are set to 12Gb. When they set to less - everything
worksfine. 
If I am oversubcribing memory - then I expect to get some "out of memory error" and see 0k free in top output.
Memory for shared buffers can not be ovesubscribed - because if kernel did not provide enough shared memory postgres
willnot start. 
If I am wrong - please, explain why and where.