Re: misc questions

Yee Man Chan wrote:
 
> 1. What is a high_water_mark and a low_water_mark?
> Are they the range of disk swap size we want to maintain?

Squid tries to keep the cache at the low water mark. The closer to high
water mark the more agressively Squid purges objects. The cache should
never go above high water mark.

> 2, Squid is doing a periodic removal policy. Is it trying to purge
> all the expired obj per period?

No, only a fraction (one hash bucket) of the cache is checked on each
period. It is far to time consuming to check the whole cache each time.

> If high_water_mark is not exceeded when storeMaintainSwapSpace
> is called, do you think it is acceptable to let it do nothing?

No, keep the high-low water marks. If it is below the low water mark
then do nothing.

> 3. Since storeGetSwapSpace is a deprecated function, why do we want
> to call storeGetSwapSpace(0) at the end of storeMaintainSwapSpace?
> Is this also a deprecated code?

Usually storeGetSwapSpace(0) does nothing, but it is a extra safeguard
to keep the cache below the high water mark. It it is above the high
water mark after the normal purging, then storeGetSwapSpace(0) very
aggresively removes objects.

---
Henrik Nordström
Sparetime Squid Hacker