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Prefer evicting expired keys when low on memory. #1790

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Prefer evicting expired keys when low on memory. #1790

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67 changes: 35 additions & 32 deletions src/redis.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2929,40 +2929,17 @@ struct evictionPoolEntry *evictionPoolAlloc(void) {
* We insert keys on place in ascending order, so keys with the smaller
* idle time are on the left, and keys with the higher idle time on the
* right. */
void evictionPoolPopulate(dictEntry **samples, int sample_count, struct evictionPoolEntry *pool) {
int j, k;

#define EVICTION_SAMPLES_ARRAY_SIZE 16
void evictionPoolPopulate(dict *sampledict, dict *keydict, struct evictionPoolEntry *pool) {
int j, k, count;
dictEntry *_samples[EVICTION_SAMPLES_ARRAY_SIZE];
dictEntry **samples;

/* Try to use a static buffer: this function is a big hit...
* Note: it was actually measured that this helps. */
if (server.maxmemory_samples <= EVICTION_SAMPLES_ARRAY_SIZE) {
samples = _samples;
} else {
samples = zmalloc(sizeof(samples[0])*server.maxmemory_samples);
}

#if 1 /* Use bulk get by default. */
count = dictGetRandomKeys(sampledict,samples,server.maxmemory_samples);
#else
count = server.maxmemory_samples;
for (j = 0; j < count; j++) samples[j] = dictGetRandomKey(sampledict);
#endif

for (j = 0; j < count; j++) {
for (j = 0; j < sample_count; j++) {
unsigned long long idle;
sds key;
robj *o;
dictEntry *de;

de = samples[j];
key = dictGetKey(de);
/* If the dictionary we are sampling from is not the main
* dictionary (but the expires one) we need to lookup the key
* again in the key dictionary to obtain the value object. */
if (sampledict != keydict) de = dictFind(keydict, key);
o = dictGetVal(de);
idle = estimateObjectIdleTime(o);

Expand Down Expand Up @@ -2999,7 +2976,6 @@ void evictionPoolPopulate(dict *sampledict, dict *keydict, struct evictionPoolEn
pool[k].key = sdsdup(key);
pool[k].idle = idle;
}
if (samples != _samples) zfree(samples);
}

int freeMemoryIfNeeded(void) {
Expand Down Expand Up @@ -3050,9 +3026,9 @@ int freeMemoryIfNeeded(void) {
if (server.maxmemory_policy == REDIS_MAXMEMORY_ALLKEYS_LRU ||
server.maxmemory_policy == REDIS_MAXMEMORY_ALLKEYS_RANDOM)
{
dict = server.db[j].dict;
dict = db->dict;
} else {
dict = server.db[j].expires;
dict = db->expires;
}
if (dictSize(dict) == 0) continue;

Expand All @@ -3071,7 +3047,31 @@ int freeMemoryIfNeeded(void) {
struct evictionPoolEntry *pool = db->eviction_pool;

while(bestkey == NULL) {
evictionPoolPopulate(dict, db->dict, db->eviction_pool);
dictEntry *samples[server.maxmemory_samples];
#if 1 /* Use bulk get by default. */
int count = dictGetRandomKeys(dict,samples,server.maxmemory_samples);
#else
int count = server.maxmemory_samples;
for (k = 0; k < count; k++) samples[k] = dictGetRandomKey(dict);
#endif
/* If the dictionary we are sampling from is not the main
* dictionary (but the expires one) we need to lookup the key
* again in the key dictionary to obtain the value object. */
if (dict != db->dict)
for (k = 0; k < count; k++) {
sds key;
dictEntry *de = samples[k];
key = dictGetKey(de);
/* Optimization: if sample is expired, just evict it instead of fussing with LRU's */
if (server.mstime > dictGetSignedIntegerVal(de)) {
bestkey = key;
break;
}
samples[k] = dictFind(db->dict, key);
}
if (bestkey) break;

evictionPoolPopulate(samples, count, db->eviction_pool);
/* Go backward from best to worst element to evict. */
for (k = REDIS_EVICTION_POOL_SIZE-1; k >= 0; k--) {
if (pool[k].key == NULL) continue;
Expand Down Expand Up @@ -3104,17 +3104,20 @@ int freeMemoryIfNeeded(void) {
else if (server.maxmemory_policy == REDIS_MAXMEMORY_VOLATILE_TTL) {
for (k = 0; k < server.maxmemory_samples; k++) {
sds thiskey;
long thisval;
long long thisval;

de = dictGetRandomKey(dict);
thiskey = dictGetKey(de);
thisval = (long) dictGetVal(de);
thisval = dictGetSignedIntegerVal(de);

/* Expire sooner (minor expire unix timestamp) is better
* candidate for deletion */
if (bestkey == NULL || thisval < bestval) {
bestkey = thiskey;
bestval = thisval;
/* Optimization: if found key is expired, not need to look further */
if (server.mstime > bestval)
break;
}
}
}
Expand Down