Re: Experimental patch for inter-page delay in VACUUM

Shridhar Daithankar wrote:

> On Tuesday 11 November 2003 18:55, Jan Wieck wrote:

>> And how does a newly mmap'ed segment propagate into a running backend?
>
> It wouldn't. Just like we allocate fixed amount of shared memory at startup
> now, we would do same for mmaped segments. Allocate maximum configured on
> startup. But it won't be into kernel space as much shared memory segment
> would be.

I don't understand that, can you explain this like you would to a child?

I want to configure my postmaster for a maximum of 256MB shared memory
(or 32768 pages), but I want to start it using 128MB (16384 pages) only.
Now while some backends that inherited the 128MB are running, I want to
increase the shared memory to 256MB, run some job and shrink it back to
128MB. How do the backends that inherited 128MB access a buffer in the
other 128MB if they happen to get a cache hit? How does that all work
with anon mmap segments?

Jan

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