[infinispan-dev] Time measurement and expiry
dan.berindei at gmail.com
Mon Oct 17 04:02:25 EDT 2011
On Sat, Oct 15, 2011 at 7:25 PM, Sanne Grinovero <sanne at infinispan.org> wrote:
> Hi all,
> I'm looking at some performance details, and noticed the current code
> is using System.currentTimeMillis() to estimate performance for short
> lived operations.
> For the purpose of CacheMgmtInterceptor we should use System.nanoTime() instead:
Very interesting, I knew that in Windows currentTimeMillis() basically
just reads a volatile because I got bit by the 15 millisecond accuracy
issue before, so I thought it would always be very fast. I had no idea
on Linux it would have the same performance as nanoTime().
> Searching for "currentTimeMillis()" in the code base reveals it's
> being used for expiry of entries as well. If someone messes with
> system clocks data will expire; is it expected that entries expire at
> calendar time and not at a set lifetime?
I would say if someone's messing with system clocks they already have
a much bigger problem than their cached data expiring...
Besides, someone may intentionally change the system time to test the
ISPN expiration algorithm :)
> I understand we need to use the absolute time to be able to transmit
> the value to other nodes, where the nanoTime of different nodes might
> not be comparable, but we could store one and use both: transmit the
> absolute value only to other nodes and refer to the other for accurate
> Other nodes receiving the absolute value will check for the remaining
> lifespane and store the corresponding nanoTime.
> ExpiryHelper itself will invoke the currentTimeMillis() operation
> internally, that means that it's going to be invoked at least once for
> each entry being accessed and might result in a lot of invocations
> when traversing several entries; I'm wondering if it shouldn't take a
> millisecond parameter to consider as current, so that this relatively
> expensive method can be invoked only once at the beginning of a batch
> of operations.
+ 1 for adding a currentTime parameter to the isExpiredX() methods in
ExpiryHelper and also to isExpired() CacheEntry and its
> Also reading this time information is a high overhead in some
> configurations, I'm wondering if we should make it possible to
> configure Infinispan to not track performance on each cache operation?
> Someone might prefer to estimate an average from multiple calls; I'm
> going to remove CacheMgmtInterceptor for my tests.
CacheMgmtInterceptor doesn't seem to be enabled when JMX statistics
are disabled, so I don't think you need to explicitly remove
CacheMgmtInterceptor for your performance tests.
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