Re: Streaming base backups

2011/1/5 Magnus Hagander <magnus(at)hagander(dot)net>:
> On Wed, Jan 5, 2011 at 22:58, Dimitri Fontaine <dimitri(at)2ndquadrant(dot)fr> wrote:
>> Magnus Hagander <magnus(at)hagander(dot)net> writes:
>>> * Stefan mentiond it might be useful to put some
>>> posix_fadvise(POSIX_FADV_DONTNEED)
>>>   in the process that streams all the files out. Seems useful, as long as that
>>>   doesn't kick them out of the cache *completely*, for other backends as well.
>>>   Do we know if that is the case?
>>
>> Maybe have a look at pgfincore to only tag DONTNEED for blocks that are
>> not already in SHM?
>
> I think that's way more complex than we want to go here.
>

DONTNEED will remove the block from OS buffer everytime.

It should not be that hard to implement a snapshot(it needs mincore())
and to restore previous state. I don't know how basebackup is
performed exactly...so perhaps I am wrong.

posix_fadvise support is already in postgresql core...we can start by
just doing a snapshot of the files before starting, or at some point
in the basebackup, it will need only 256kB per GB of data...
--
Cédric Villemain               2ndQuadrant
http://2ndQuadrant.fr/     PostgreSQL : Expertise, Formation et Support