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Obtain LRU clock in a resolution dependent way.

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For testing purposes it is handy to have a very high resolution of the
LRU clock, so that it is possible to experiment with scripts running in
just a few seconds how the eviction algorithms works.

This commit allows Redis to use the cached LRU clock, or a value
computed on demand, depending on the resolution. So normally we have the
good performance of a precomputed value, and a clock that wraps in many
days using the normal resolution, but if needed, changing a define will
switch behavior to an high resolution LRU clock.
This commit is contained in:
antirez
2014-03-20 11:47:12 +01:00
parent 561e793472
commit 205c2ccc0c
4 changed files with 25 additions and 19 deletions
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26
src/redis.c
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@ -843,9 +843,8 @@ void activeExpireCycle(int type) {
}
}
void updateLRUClock(void) {
server.lruclock = (mstime()/REDIS_LRU_CLOCK_RESOLUTION) &
REDIS_LRU_CLOCK_MAX;
unsigned int getLRUClock(void) {
return (mstime()/REDIS_LRU_CLOCK_RESOLUTION) & REDIS_LRU_CLOCK_MAX;
}
/* Add a sample to the operations per second array of samples. */
@ -1044,19 +1043,18 @@ int serverCron(struct aeEventLoop *eventLoop, long long id, void *clientData) {
run_with_period(100) trackOperationsPerSecond();
/* We have just 22 bits per object for LRU information.
* So we use an (eventually wrapping) LRU clock with 10 seconds resolution.
* 2^22 bits with 10 seconds resolution is more or less 1.5 years.
/* We have just REDIS_LRU_BITS bits per object for LRU information.
* So we use an (eventually wrapping) LRU clock.
*
* Note that even if this will wrap after 1.5 years it's not a problem,
* everything will still work but just some object will appear younger
* to Redis. But for this to happen a given object should never be touched
* for 1.5 years.
* Note that even if the counter wraps it's not a big problem,
* everything will still work but some object will appear younger
* to Redis. However for this to happen a given object should never be
* touched for all the time needed to the counter to wrap, which is
* not likely.
*
* Note that you can change the resolution altering the
* REDIS_LRU_CLOCK_RESOLUTION define.
*/
updateLRUClock();
* REDIS_LRU_CLOCK_RESOLUTION define. */
server.lruclock = getLRUClock();
/* Record the max memory used since the server was started. */
if (zmalloc_used_memory() > server.stat_peak_memory)
@ -1421,7 +1419,7 @@ void initServerConfig() {
server.migrate_cached_sockets = dictCreate(&migrateCacheDictType,NULL);
server.loading_process_events_interval_bytes = (1024*1024*2);
updateLRUClock();
server.lruclock = getLRUClock();
resetServerSaveParams();
appendServerSaveParams(60*60,1); /* save after 1 hour and 1 change */