diff options
Diffstat (limited to 'utils/lru/lfu-simulation.c')
| -rw-r--r-- | utils/lru/lfu-simulation.c | 163 |
1 files changed, 163 insertions, 0 deletions
diff --git a/utils/lru/lfu-simulation.c b/utils/lru/lfu-simulation.c new file mode 100644 index 000000000..ebfc434ac --- /dev/null +++ b/utils/lru/lfu-simulation.c @@ -0,0 +1,163 @@ +#include <stdio.h> +#include <time.h> +#include <stdint.h> +#include <stdlib.h> + +int decr_every = 1; +int keyspace_size = 1000000; +time_t switch_after = 30; /* Switch access pattern after N seconds. */ + +struct entry { + /* Field that the LFU Redis implementation will have (we have + * 24 bits of total space in the object->lru field). */ + uint8_t counter; /* Logarithmic counter. */ + uint16_t decrtime; /* (Reduced precision) time of last decrement. */ + + /* Fields only useful for visualization. */ + uint64_t hits; /* Number of real accesses. */ + time_t ctime; /* Key creation time. */ +}; + +#define to_16bit_minutes(x) ((x/60) & 65535) +#define COUNTER_INIT_VAL 5 + +/* Compute the difference in minutes between two 16 bit minutes times + * obtained with to_16bit_minutes(). Since they can wrap around if + * we detect the overflow we account for it as if the counter wrapped + * a single time. */ +uint16_t minutes_diff(uint16_t now, uint16_t prev) { + if (now >= prev) return now-prev; + return 65535-prev+now; +} + +/* Increment a couter logaritmically: the greatest is its value, the + * less likely is that the counter is really incremented. + * The maximum value of the counter is saturated at 255. */ +uint8_t log_incr(uint8_t counter) { + if (counter == 255) return counter; + double r = (double)rand()/RAND_MAX; + double baseval = counter-COUNTER_INIT_VAL; + if (baseval < 0) baseval = 0; + double limit = 1.0/(baseval*10+1); + if (r < limit) counter++; + return counter; +} + +/* Simulate an access to an entry. */ +void access_entry(struct entry *e) { + e->counter = log_incr(e->counter); + e->hits++; +} + +/* Return the entry LFU value and as a side effect decrement the + * entry value if the decrement time was reached. */ +uint8_t scan_entry(struct entry *e) { + if (minutes_diff(to_16bit_minutes(time(NULL)),e->decrtime) + >= decr_every) + { + if (e->counter) { + if (e->counter > COUNTER_INIT_VAL*2) { + e->counter /= 2; + } else { + e->counter--; + } + } + e->decrtime = to_16bit_minutes(time(NULL)); + } + return e->counter; +} + +/* Print the entry info. */ +void show_entry(long pos, struct entry *e) { + char *tag = "normal "; + + if (pos >= 10 && pos <= 14) tag = "new no access"; + if (pos >= 15 && pos <= 19) tag = "new accessed "; + if (pos >= keyspace_size -5) tag= "old no access"; + + printf("%ld] <%s> frequency:%d decrtime:%d [%lu hits | age:%ld seconds]\n", + pos, tag, e->counter, e->decrtime, (unsigned long)e->hits, + time(NULL) - e->ctime); +} + +int main(void) { + time_t start = time(NULL); + time_t new_entry_time = start; + time_t display_time = start; + struct entry *entries = malloc(sizeof(*entries)*keyspace_size); + long j; + + /* Initialize. */ + for (j = 0; j < keyspace_size; j++) { + entries[j].counter = COUNTER_INIT_VAL; + entries[j].decrtime = to_16bit_minutes(start); + entries[j].hits = 0; + entries[j].ctime = time(NULL); + } + + while(1) { + time_t now = time(NULL); + long idx; + + /* Scan N random entries (simulates the eviction under maxmemory). */ + for (j = 0; j < 3; j++) { + scan_entry(entries+(rand()%keyspace_size)); + } + + /* Access a random entry: use a power-law access pattern up to + * 'switch_after' seconds. Then revert to flat access pattern. */ + if (now-start < switch_after) { + /* Power law. */ + #if 0 + idx = keyspace_size; + while(rand() % 2 && idx > 1) idx /= 2; + idx = rand() % idx; + #endif + idx = 1; + while((rand() % 21) != 0 && idx < keyspace_size) idx *= 2; + if (idx > keyspace_size) idx = keyspace_size; + idx = rand() % idx; + } else { + /* Flat. */ + idx = rand() % keyspace_size; + } + + /* Never access entries between position 10 and 14, so that + * we simulate what happens to new entries that are never + * accessed VS new entries which are accessed in positions + * 15-19. + * + * Also never access last 5 entry, so that we have keys which + * are never recreated (old), and never accessed. */ + if ((idx < 10 || idx > 14) && (idx < keyspace_size-5)) + access_entry(entries+idx); + + /* Simulate the addition of new entries at positions between + * 10 and 19, a random one every 10 seconds. */ + if (new_entry_time == now) { + idx = 10+(rand()%10); + entries[idx].counter = COUNTER_INIT_VAL; + entries[idx].decrtime = to_16bit_minutes(start); + entries[idx].hits = 0; + entries[idx].ctime = time(NULL); + new_entry_time = now+10; + } + + /* Show the first 20 entries and the last 20 entries. */ + if (display_time != now) { + printf("=============================\n"); + printf("Current minutes time: %d\n", (int)to_16bit_minutes(now)); + printf("Access method: %s\n", + (now-start < switch_after) ? "power-law" : "flat"); + + for (j = 0; j < 20; j++) + show_entry(j,entries+j); + + for (j = keyspace_size-20; j < keyspace_size; j++) + show_entry(j,entries+j); + display_time = now; + } + } + return 0; +} + |