Re: Experimental patch for inter-page delay in VACUUM

Jan Wieck wrote:
> Bruce Momjian wrote:
> 
> > Jan Wieck wrote:
> >> Bruce Momjian wrote:
> >> 
> >> > Now, O_SYNC is going to force every write to the disk.  If we have a
> >> > transaction that has to write lots of buffers (has to write them to
> >> > reuse the shared buffer)
> >> 
> >> So make the background writer/checkpointer keeping the LRU head clean. I 
> >> explained that 3 times now.
> > 
> > If the background cleaner has to not just write() but write/fsync or
> > write/O_SYNC, it isn't going to be able to clean them fast enough.  It
> > creates a bottleneck where we didn't have one before.
> > 
> > We are trying to eliminate an I/O storm during checkpoint, but the
> > solutions seem to be making the non-checkpoint times slower.
> > 
> 
> It looks as if you're assuming that I am making the backends unable to 
> write on their own, so that they have to wait on the checkpointer. I 
> never said that.

Maybe I missed it but are those backend now doing write or write/fsync? 
If the former, that is fine.  If the later, it does seem slower than it
used to be.

--  Bruce Momjian                        |  http://candle.pha.pa.us pgman@candle.pha.pa.us               |  (610)
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