Re: Background writer committed

TODO updated:

* -Use background process to write dirty shared buffers to disk

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Jan Wieck wrote:
> I committed the first part of the background writer process. We had a
> consensus on attempting to avoid write() calls from regular backends,
> but did no come to any conclusions what to do to force the kernel to
> actually do some IO.
>
> Consequently, this patch is a separate process launched by postmaster,
> that periodically write()'s out "some" dirty buffers in LRU order. This
> causes the buffers returned for replacement (when a backend needs to
> read in a page) to be clean allways. The process does no sync(), fsync()
> or any other calls thus far. Nothing has changed in the checkpoint logic
> either.
>
> The configuration options controlling the process are all PGC_SIGHUP:
>
> # - Background writer -
> #bgwriter_delay = 200 # 10-5000 milliseconds
> #bgwriter_percent = 1 # 0-100% of dirty buffers
> #bgwriter_maxpages = 100 # 1-1000 buffers max at once
>
> Delay is the number of milliseconds to wait between loops. If there was
> nothing to do at all in one loop (all buffers clean), then the process
> will sleep for 10 seconds.
>
> Percent is the percentage of "dirty pages" to write per loop. This is
> independant of the size of the buffer pool. If percent = 0 the
> postmaster will not start the process at all.
>
> Maxpages is an upper bound to prevent the background writer from
> producing a write storm if a sequential operation causes all pages of a
> large buffer pool to be dirtied at once.
>
>
> Jan
>
> --
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> # It's easier to get forgiveness for being wrong than for being right. #
> # Let's break this rule - forgive me. #
> #================================================== JanWieck(at)Yahoo(dot)com #
>
>
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