On Fri, 2004-12-31 at 01:14, Bruce Momjian wrote: > Simon Riggs wrote: > > On Mon, 2004-12-27 at 22:21, Bruce Momjian wrote: > > > Should we consider at least adjusting the meaning of bgwriter_percent? > > > > Yes. As things stand, this is the only change that seems safe. > > > > Here's a very short patch that implements this change within BufferSync > > in bufmgr.c > > > > - No algorithm changes > > - No error message changes > > - Only change is the call to StrategyDirtyBufferList is made using the > > maximum number of buffers that will be cleaned, rather than uselessly > > trawling through all of shared_buffers > > > > This changes the meaning of bgwriter_percent from "percent of dirty > > buffers" to "percent of shared_buffers". The default settings of 1% of > > 1000 buffers gives up to 10 dirty block writes every 250ms > > > > Benefit: allows performance tuning by increases options for setting > > bgwriter_delay which would otherwise have an ineffectually high minimum > > setting > > > > Risk: low > > > > 1-line doc patch to follow, if this is approved. > > I am not objecting to the patch, but what value is there in having both > bgwriter_percent and bgwriter_maxpages? Seems both are redundant and > that one would be enough.
In brief: i) for now: as little change as possible is good ii) the two parameters are OK iii) trying to decide an alternative takes time, which we do not have iv) what is presented here is simply a performance bug fix, not the best long term alternative... I'd like to move quickly: if we do this (or an alternative), it has to be done soon and it would be easy to discuss this until we run out of time. Could we vote: in RC3, or not? In more detail... The value of having both is: i) as little change as possible at this stage of RC - the main one ...which gives us stability ...and also avoids having to re-discuss what they *should* be ii) Having two isn't that bad. bgwriter_percent auto adjusts the length of the to-be-cleaned-list, so it is roughly useful anywhere between 500 and 10000 shared_buffers. That is IMHO slightly more useful than a hard definition set via bgwriter_maxpages, since that is likely to be set wrong anyway - but has some value as an outside limit on the number of pages. [You may wish to set shared_buffers > 10000 even on smaller servers, since many now have 2GB RAM and yet a relatively poor I/O subsystem. Having maxpages set separately allows the majority of people to set shared_buffers higher without swamping their I/O subsystems because they didn't know about the r8.0 bgwriter feature/parameters] iii) changing the parameters might tempt us towards changing the algorithm, which is not a topic we have reached agreement on iv) I see it as a goal to remove all of those parameters anyway, as well as explore some of the many options and ideas everybody has presented, so further change is likely at the next release whatever is done now. The patch is as simple as I can make it and yet remove the unnecessary performance effect in the existing code. Thanks to Neil and others for showing that this was possible...I see this patch as a team effort. I've already spoken against larger change and would do so again now: if we don't agree this change, then I would vote for no-change.... simply because this patch is minimal change. We *suspect* further change is beneficial but we have no evidence to support what that change should be, amongst the large range of possible solutions proposed. -- Best Regards, Simon Riggs ---------------------------(end of broadcast)--------------------------- TIP 2: you can get off all lists at once with the unregister command (send "unregister YourEmailAddressHere" to [EMAIL PROTECTED])