Re: Experimental patch for inter-page delay in VACUUM

Shridhar Daithankar wrote:
> On Tuesday 11 November 2003 00:50, Neil Conway wrote:
>> Jan Wieck <JanWieck(at)Yahoo(dot)com> writes:
>> > We can't resize shared memory because we allocate the whole thing in
>> > one big hump - which causes the shmmax problem BTW. If we allocate
>> > that in chunks of multiple blocks, we only have to give it a total
>> > maximum size to get the hash tables and other stuff right from the
>> > beginning. But the vast majority of memory, the buffers themself, can
>> > be made adjustable at runtime.
>>
>> Yeah, writing a palloc()-style wrapper over shm has been suggested
>> before (by myself among others). You could do the shm allocation in
>> fixed-size blocks (say, 1 MB each), and then do our own memory
>> management to allocate and release smaller chunks of shm when
>> requested. I'm not sure what it really buys us, though: sure, we can
>> expand the shared buffer area to some degree, but
>
> Thinking of it, it can be put as follows. Postgresql needs shared memory
> between all the backends.
>
> If the parent postmaster mmaps anonymous memory segments and shares them with
> children, postgresql wouldn't be dependent upon any kernel resourse aka
> shared memory anymore.

And how does a newly mmap'ed segment propagate into a running backend?

Jan

>
> Furthermore parent posmaster can allocate different anonymous mappings for
> different databases. In addition to postgresql buffer manager overhaul, this
> would make things lot better.
>
> note that I am not suggesting mmap to maintain files on disk. So I guess that
> should be OK.
>
> I tried searching for mmap on hackers. The threads seem to be very old. One in
> 1998. with so many proposals of rewriting core stuff, does this have any
> chance?
>
> Just a thought.
>
> Shridhar
>
>
> ---------------------------(end of broadcast)---------------------------
> TIP 2: you can get off all lists at once with the unregister command
> (send "unregister YourEmailAddressHere" to majordomo(at)postgresql(dot)org)

--
#======================================================================#
# It's easier to get forgiveness for being wrong than for being right. #
# Let's break this rule - forgive me. #
#================================================== JanWieck(at)Yahoo(dot)com #