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coocood
Replace `time.Now` with lower precision time source
time.Now() will sometimes result in a full system call (this is the default on AWS EC2 instances). I think for an LRU you can probably get away with second precision. One option would be to have a background goroutine that called time.Now() every second and cached the result globally.
I have proposed to replace wall time time.Now() by a custom timer in #69. Then you could create you own custom time structure with field seconds and update it periodically with a Go timer.
@pheepi @bartle-stripe Did you implement the background goroutine time.Now() timer? If so, would you be willing to share the code here?
@coocood For reference, this is what the pprof data looks like when trying to set tens of millions of entries in an AWS Fargate task. Roughly 60% of the CPU for setting items is being spent in time.now()
This resulted in ~50% speedup for calls to .Set()
type lowResClock struct {
now uint32
}
func newLosResClock() lowResClock {
clock := lowResClock{
now: uint32(time.Now().Unix()),
}
ticker := time.NewTicker(1 * time.Second)
go func() {
for {
select {
case _ = <-ticker.C:
clock.now = uint32(time.Now().Unix())
}
}
}()
return clock
}
func (clock lowResClock) Now() uint32 {
return clock.now
}
@coocood Do you think the performance improvement from this is worth replacing the existing default implementation?
@thesilentg
The lowResClock starts a goroutine and never exit, if cache are created and discarded too many times, there would be a lot of goroutines leaked.
And clock.now needs atomic access to be race-free.
We could create a well-implemented builtin lowResClock, but I think the default should still be time.Now()
Optimized timer with cached value is now part of the code passed as a custom parameter of NewCacheCustomTimer in #88. Create new stoppable timer with NewCachedTimer and call Stop() method when your cache is no more in use. The method stops the background routine that periodically updates the time.