Re: refusing connections based on load ...

The Hermit Hacker wrote:
> Agreed ... by default, the loadavg method could be set to zero, to ignore
> ... I don't care if I'm off by 1min before I catch the increase, the fact
> is that I have caught it, and prevent any new ones coming in until it
> drops off again ...
>
> Make it two variables:
>
> transla
> rejectla
>
> if transla is hit, restrict on transactions, letting others connect, but
> putting them on hold while the la drops again ... if it goes above
> rejectla, refuse new connections altogether ...
>
> so now I can set something like:
>
> transla = 8
> rejectla = 16
>
> but if loadavg goes above 16, I want to get rid of what is causing the
> load to rise *before* adding new variables to the mix that will cause it
> to rise higher ...
>
> and your arg about permissions (Tom's, not Peter's) is moot in at least 3
> of the major systems (Linux, *BSD and Solaris) as there is a getloadavg()
> function in all three for doing this ...

I've just recompiled my php4 module to get sysvsem support
and limited the number of concurrent DB transactions on the
application level. The (not yet finished) TPC-C
implementation I'm working on scales about 3-4 times better
now. That's an improvement!

This proves that limiting the number of concurrently running
transactions is sufficient to keep the system load down.
Combined these two look as follows:

- We start with a fairly high setting in the semaphore.

- When the system load exceeds the high-watermark, we don't
increment the semaphore back after transaction end (need
to ensure that at least a small minimum of xacts is left,
but that's easy).

- When the system goes back to normal load level, we slowly
increase the semaphore again.

This way we might have some peek pushing the system against
the wall for a moment. If that doesn't go away quickly, we
just delay users (who see some delay anyway actually).

Jan

--

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# It's easier to get forgiveness for being wrong than for being right. #
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