Add expire.c and evict.c.

src/evict.c

@@ -0,0 +1,364 @@
+/* Maxmemory directive handling (LRU eviction and other policies).
+ *
+ * ----------------------------------------------------------------------------
+ *
+ * Copyright (c) 2009-2016, Salvatore Sanfilippo <antirez at gmail dot com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ *   * Redistributions of source code must retain the above copyright notice,
+ *     this list of conditions and the following disclaimer.
+ *   * Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions and the following disclaimer in the
+ *     documentation and/or other materials provided with the distribution.
+ *   * Neither the name of Redis nor the names of its contributors may be used
+ *     to endorse or promote products derived from this software without
+ *     specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "server.h"
+#include "bio.h"
+
+/* Return the LRU clock, based on the clock resolution. This is a time
+ * in a reduced-bits format that can be used to set and check the
+ * object->lru field of redisObject structures. */
+unsigned int getLRUClock(void) {
+    return (mstime()/LRU_CLOCK_RESOLUTION) & LRU_CLOCK_MAX;
+}
+
+/* Given an object returns the min number of milliseconds the object was never
+ * requested, using an approximated LRU algorithm. */
+unsigned long long estimateObjectIdleTime(robj *o) {
+    unsigned long long lruclock = LRU_CLOCK();
+    if (lruclock >= o->lru) {
+        return (lruclock - o->lru) * LRU_CLOCK_RESOLUTION;
+    } else {
+        return (lruclock + (LRU_CLOCK_MAX - o->lru)) *
+                    LRU_CLOCK_RESOLUTION;
+    }
+}
+
+/* freeMemoryIfNeeded() gets called when 'maxmemory' is set on the config
+ * file to limit the max memory used by the server, before processing a
+ * command.
+ *
+ * The goal of the function is to free enough memory to keep Redis under the
+ * configured memory limit.
+ *
+ * The function starts calculating how many bytes should be freed to keep
+ * Redis under the limit, and enters a loop selecting the best keys to
+ * evict accordingly to the configured policy.
+ *
+ * If all the bytes needed to return back under the limit were freed the
+ * function returns C_OK, otherwise C_ERR is returned, and the caller
+ * should block the execution of commands that will result in more memory
+ * used by the server.
+ *
+ * ------------------------------------------------------------------------
+ *
+ * LRU approximation algorithm
+ *
+ * Redis uses an approximation of the LRU algorithm that runs in constant
+ * memory. Every time there is a key to expire, we sample N keys (with
+ * N very small, usually in around 5) to populate a pool of best keys to
+ * evict of M keys (the pool size is defined by MAXMEMORY_EVICTION_POOL_SIZE).
+ *
+ * The N keys sampled are added in the pool of good keys to expire (the one
+ * with an old access time) if they are better than one of the current keys
+ * in the pool.
+ *
+ * After the pool is populated, the best key we have in the pool is expired.
+ * However note that we don't remove keys from the pool when they are deleted
+ * so the pool may contain keys that no longer exist.
+ *
+ * When we try to evict a key, and all the entries in the pool don't exist
+ * we populate it again. This time we'll be sure that the pool has at least
+ * one key that can be evicted, if there is at least one key that can be
+ * evicted in the whole database. */
+
+/* Create a new eviction pool. */
+struct evictionPoolEntry *evictionPoolAlloc(void) {
+    struct evictionPoolEntry *ep;
+    int j;
+
+    ep = zmalloc(sizeof(*ep)*MAXMEMORY_EVICTION_POOL_SIZE);
+    for (j = 0; j < MAXMEMORY_EVICTION_POOL_SIZE; j++) {
+        ep[j].idle = 0;
+        ep[j].key = NULL;
+    }
+    return ep;
+}
+
+/* This is an helper function for freeMemoryIfNeeded(), it is used in order
+ * to populate the evictionPool with a few entries every time we want to
+ * expire a key. Keys with idle time smaller than one of the current
+ * keys are added. Keys are always added if there are free entries.
+ *
+ * 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. */
+
+#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);
+    }
+
+    count = dictGetSomeKeys(sampledict,samples,server.maxmemory_samples);
+    for (j = 0; j < 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);
+
+        /* Insert the element inside the pool.
+         * First, find the first empty bucket or the first populated
+         * bucket that has an idle time smaller than our idle time. */
+        k = 0;
+        while (k < MAXMEMORY_EVICTION_POOL_SIZE &&
+               pool[k].key &&
+               pool[k].idle < idle) k++;
+        if (k == 0 && pool[MAXMEMORY_EVICTION_POOL_SIZE-1].key != NULL) {
+            /* Can't insert if the element is < the worst element we have
+             * and there are no empty buckets. */
+            continue;
+        } else if (k < MAXMEMORY_EVICTION_POOL_SIZE && pool[k].key == NULL) {
+            /* Inserting into empty position. No setup needed before insert. */
+        } else {
+            /* Inserting in the middle. Now k points to the first element
+             * greater than the element to insert.  */
+            if (pool[MAXMEMORY_EVICTION_POOL_SIZE-1].key == NULL) {
+                /* Free space on the right? Insert at k shifting
+                 * all the elements from k to end to the right. */
+                memmove(pool+k+1,pool+k,
+                    sizeof(pool[0])*(MAXMEMORY_EVICTION_POOL_SIZE-k-1));
+            } else {
+                /* No free space on right? Insert at k-1 */
+                k--;
+                /* Shift all elements on the left of k (included) to the
+                 * left, so we discard the element with smaller idle time. */
+                sdsfree(pool[0].key);
+                memmove(pool,pool+1,sizeof(pool[0])*k);
+            }
+        }
+        pool[k].key = sdsdup(key);
+        pool[k].idle = idle;
+    }
+    if (samples != _samples) zfree(samples);
+}
+
+int freeMemoryIfNeeded(void) {
+    size_t mem_reported, mem_used, mem_tofree, mem_freed;
+    int slaves = listLength(server.slaves);
+    mstime_t latency, eviction_latency;
+    long long delta;
+
+    /* Check if we are over the memory usage limit. If we are not, no need
+     * to subtract the slaves output buffers. We can just return ASAP. */
+    mem_reported = zmalloc_used_memory();
+    if (mem_reported <= server.maxmemory) return C_OK;
+
+    /* Remove the size of slaves output buffers and AOF buffer from the
+     * count of used memory. */
+    mem_used = mem_reported;
+    if (slaves) {
+        listIter li;
+        listNode *ln;
+
+        listRewind(server.slaves,&li);
+        while((ln = listNext(&li))) {
+            client *slave = listNodeValue(ln);
+            unsigned long obuf_bytes = getClientOutputBufferMemoryUsage(slave);
+            if (obuf_bytes > mem_used)
+                mem_used = 0;
+            else
+                mem_used -= obuf_bytes;
+        }
+    }
+    if (server.aof_state != AOF_OFF) {
+        mem_used -= sdslen(server.aof_buf);
+        mem_used -= aofRewriteBufferSize();
+    }
+
+    /* Check if we are still over the memory limit. */
+    if (mem_used <= server.maxmemory) return C_OK;
+
+    /* Compute how much memory we need to free. */
+    mem_tofree = mem_used - server.maxmemory;
+    mem_freed = 0;
+
+    if (server.maxmemory_policy == MAXMEMORY_NO_EVICTION)
+        goto cant_free; /* We need to free memory, but policy forbids. */
+
+    latencyStartMonitor(latency);
+    while (mem_freed < mem_tofree) {
+        int j, k, keys_freed = 0;
+
+        for (j = 0; j < server.dbnum; j++) {
+            long bestval = 0; /* just to prevent warning */
+            sds bestkey = NULL;
+            dictEntry *de;
+            redisDb *db = server.db+j;
+            dict *dict;
+
+            if (server.maxmemory_policy == MAXMEMORY_ALLKEYS_LRU ||
+                server.maxmemory_policy == MAXMEMORY_ALLKEYS_RANDOM)
+            {
+                dict = server.db[j].dict;
+            } else {
+                dict = server.db[j].expires;
+            }
+            if (dictSize(dict) == 0) continue;
+
+            /* volatile-random and allkeys-random policy */
+            if (server.maxmemory_policy == MAXMEMORY_ALLKEYS_RANDOM ||
+                server.maxmemory_policy == MAXMEMORY_VOLATILE_RANDOM)
+            {
+                de = dictGetRandomKey(dict);
+                bestkey = dictGetKey(de);
+            }
+
+            /* volatile-lru and allkeys-lru policy */
+            else if (server.maxmemory_policy == MAXMEMORY_ALLKEYS_LRU ||
+                server.maxmemory_policy == MAXMEMORY_VOLATILE_LRU)
+            {
+                struct evictionPoolEntry *pool = db->eviction_pool;
+
+                while(bestkey == NULL) {
+                    evictionPoolPopulate(dict, db->dict, db->eviction_pool);
+                    /* Go backward from best to worst element to evict. */
+                    for (k = MAXMEMORY_EVICTION_POOL_SIZE-1; k >= 0; k--) {
+                        if (pool[k].key == NULL) continue;
+                        de = dictFind(dict,pool[k].key);
+
+                        /* Remove the entry from the pool. */
+                        sdsfree(pool[k].key);
+                        /* Shift all elements on its right to left. */
+                        memmove(pool+k,pool+k+1,
+                            sizeof(pool[0])*(MAXMEMORY_EVICTION_POOL_SIZE-k-1));
+                        /* Clear the element on the right which is empty
+                         * since we shifted one position to the left.  */
+                        pool[MAXMEMORY_EVICTION_POOL_SIZE-1].key = NULL;
+                        pool[MAXMEMORY_EVICTION_POOL_SIZE-1].idle = 0;
+
+                        /* If the key exists, is our pick. Otherwise it is
+                         * a ghost and we need to try the next element. */
+                        if (de) {
+                            bestkey = dictGetKey(de);
+                            break;
+                        } else {
+                            /* Ghost... */
+                            continue;
+                        }
+                    }
+                }
+            }
+
+            /* volatile-ttl */
+            else if (server.maxmemory_policy == MAXMEMORY_VOLATILE_TTL) {
+                for (k = 0; k < server.maxmemory_samples; k++) {
+                    sds thiskey;
+                    long thisval;
+
+                    de = dictGetRandomKey(dict);
+                    thiskey = dictGetKey(de);
+                    thisval = (long) dictGetVal(de);
+
+                    /* Expire sooner (minor expire unix timestamp) is better
+                     * candidate for deletion */
+                    if (bestkey == NULL || thisval < bestval) {
+                        bestkey = thiskey;
+                        bestval = thisval;
+                    }
+                }
+            }
+
+            /* Finally remove the selected key. */
+            if (bestkey) {
+                robj *keyobj = createStringObject(bestkey,sdslen(bestkey));
+                propagateExpire(db,keyobj,server.lazyfree_lazy_eviction);
+                /* We compute the amount of memory freed by db*Delete() alone.
+                 * It is possible that actually the memory needed to propagate
+                 * the DEL in AOF and replication link is greater than the one
+                 * we are freeing removing the key, but we can't account for
+                 * that otherwise we would never exit the loop.
+                 *
+                 * AOF and Output buffer memory will be freed eventually so
+                 * we only care about memory used by the key space. */
+                delta = (long long) zmalloc_used_memory();
+                latencyStartMonitor(eviction_latency);
+                if (server.lazyfree_lazy_eviction)
+                    dbAsyncDelete(db,keyobj);
+                else
+                    dbSyncDelete(db,keyobj);
+                latencyEndMonitor(eviction_latency);
+                latencyAddSampleIfNeeded("eviction-del",eviction_latency);
+                latencyRemoveNestedEvent(latency,eviction_latency);
+                delta -= (long long) zmalloc_used_memory();
+                mem_freed += delta;
+                server.stat_evictedkeys++;
+                notifyKeyspaceEvent(NOTIFY_EVICTED, "evicted",
+                    keyobj, db->id);
+                decrRefCount(keyobj);
+                keys_freed++;
+
+                /* When the memory to free starts to be big enough, we may
+                 * start spending so much time here that is impossible to
+                 * deliver data to the slaves fast enough, so we force the
+                 * transmission here inside the loop. */
+                if (slaves) flushSlavesOutputBuffers();
+            }
+        }
+        if (!keys_freed) {
+            latencyEndMonitor(latency);
+            latencyAddSampleIfNeeded("eviction-cycle",latency);
+            goto cant_free; /* nothing to free... */
+        }
+    }
+    latencyEndMonitor(latency);
+    latencyAddSampleIfNeeded("eviction-cycle",latency);
+    return C_OK;
+
+cant_free:
+    /* We are here if we are not able to reclaim memory. There is only one
+     * last thing we can try: check if the lazyfree thread has jobs in queue
+     * and wait... */
+    while(bioPendingJobsOfType(BIO_LAZY_FREE)) {
+        if (((mem_reported - zmalloc_used_memory()) + mem_freed) >= mem_tofree)
+            break;
+        usleep(1000);
+    }
+    return C_ERR;
+}
+