Re: bgwriter changes

On 12/14/2004 2:40 PM, Tom Lane wrote:

> "Zeugswetter Andreas DAZ SD" <ZeugswetterA(at)spardat(dot)at> writes:
>> Is it possible to do a patch that produces a dirty buffer list in LRU order
>> and stops early when eighter maxpages is reached or bgwriter_percent
>> pages are scanned ?
>
> Only if you redefine the meaning of bgwriter_percent. At present it's
> defined by reference to the total number of dirty pages, and that can't
> be known without collecting them all.
>
> If it were, say, a percentage of the total length of the T1/T2 lists,
> then we'd have some chance of stopping the scan early.

That definition is identical to a fixed maximum number of pages to write
per call. And since that parameter exists too, it would be redundant.

The other way around would make sense. In order to avoid writing the
busiest buffers at all (except for checkpoinging), the parameter should
mean "don't scan the last x% of the queue at all".

Still, we need to avoid scanning over all the clean blocks of a large
buffer pool, so there is need for a separate dirty-LRU.

Jan

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