Re: Set hint bits upon eviction from BufMgr

On Mon, Mar 28, 2011 at 9:29 AM, Kevin Grittner
<Kevin(dot)Grittner(at)wicourts(dot)gov> wrote:
> Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
>> The major problem with all of this is that the bgwriter has no
>> idea which buffers contain heap pages.  And I'm not convinced it's
>> a good idea to try to let it know that.  If we get to the point
>> where bgwriter is trying to do catalog accesses, we are in for a
>> world of pain. (Can you say "modularity violation"?  How about
>> "deadlock"?)
>
> How about having a BackgroundPrepareForWriteFunction variable
> associated with each page the bgwriter might see, which would be a
> pointer to a function to call (if the variable is not NULL) before
> writing?  The bgwriter would still have no idea what kind of page it
> was or what the function did....

Well, that is much cleaner from abstraction point of view but you lose
the ability to adjust scan priority before flushing out the page...I'm
assuming by the time this function is called, you've already made the
decision to write it out. (maybe priority is necessary and maybe it
isn't, but I don't like losing the ability to tune at that level).

You could though put a priority inspection facility behind a similar
abstraction fence (BackgroundGetWritePriority) though. Maybe that's
more trouble than it's worth though.

merlin