X-Git-Url: https://git.saurik.com/redis.git/blobdiff_plain/a440ecf0d36d22305f994a4482e60099720c47f3..452229b6fb0251f82d9caa5388db1160f10bc2d5:/src/dscache.c diff --git a/src/dscache.c b/src/dscache.c index cd2ef850..8243e794 100644 --- a/src/dscache.c +++ b/src/dscache.c @@ -19,76 +19,33 @@ /* TODO: * - * - The WATCH helper will be used to signal the cache system - * we need to flush a given key/dbid into disk, adding this key/dbid - * pair into a server.ds_cache_dirty linked list AND hash table (so that we - * don't add the same thing multiple times). - * - * - cron() checks if there are elements on this list. When there are things - * to flush, we create an IO Job for the I/O thread. - * NOTE: We disalbe object sharing when server.ds_enabled == 1 so objects - * that are referenced an IO job for flushing on disk are marked as - * o->storage == REDIS_DS_SAVING. - * - * - This is what we do on key lookup: - * 1) The key already exists in memory. object->storage == REDIS_DS_MEMORY - * or it is object->storage == REDIS_DS_DIRTY: - * We don't do nothing special, lookup, return value object pointer. - * 2) The key is in memory but object->storage == REDIS_DS_SAVING. - * When this happens we block waiting for the I/O thread to process - * this object. Then continue. - * 3) The key is not in memory. We block to load the key from disk. - * Of course the key may not be present at all on the disk store as well, - * in such case we just detect this condition and continue, returning - * NULL from lookup. - * - * - Preloading of needed keys: - * 1) As it was done with VM, also with this new system we try preloading - * keys a client is going to use. We block the client, load keys - * using the I/O thread, unblock the client. Same code as VM more or less. - * - * - Reclaiming memory. - * In cron() we detect our memory limit was reached. What we - * do is deleting keys that are REDIS_DS_MEMORY, using LRU. - * - * If this is not enough to return again under the memory limits we also - * start to flush keys that need to be synched on disk synchronously, - * removing it from the memory. We do this blocking as memory limit is a - * much "harder" barrirer in the new design. - * - * - IO thread operations are no longer stopped for sync loading/saving of - * things. When a key is found to be in the process of being saved - * we simply wait for the IO thread to end its work. - * - * Otherwise if there is to load a key without any IO thread operation - * just started it is blocking-loaded in the lookup function. + * WARNING: most of the following todo items and design issues are no + * longer relevant with the new design. Here as a checklist to see if + * some old ideas still apply. * * - What happens when an object is destroyed? * - * If o->storage == REDIS_DS_MEMORY then we simply destory the object. - * If o->storage == REDIS_DS_DIRTY we can still remove the object. It had - * changes not flushed on disk, but is being removed so - * who cares. - * if o->storage == REDIS_DS_SAVING then the object is being saved so - * it is impossible that its refcount == 1, must be at - * least two. When the object is saved the storage will - * be set back to DS_MEMORY. + * If the object is destroyed since semantically it was deleted or + * replaced with something new, we don't care if there was a SAVE + * job pending for it. Anyway when the IO JOb will be created we'll get + * the pointer of the current value. * - * - What happens when keys are deleted? - * - * We simply schedule a key flush operation as usually, but when the - * IO thread will be created the object pointer will be set to NULL - * so the IO thread will know that the work to do is to delete the key - * from the disk store. + * If the object is already a REDIS_IO_SAVEINPROG object, then it is + * impossible that we get a decrRefCount() that will reach refcount of zero + * since the object is both in the dataset and in the io job entry. * * - What happens with MULTI/EXEC? * - * Good question. + * Good question. Without some kind of versioning with a global counter + * it is not possible to have trasactions on disk, but they are still + * useful since from the point of view of memory and client bugs it is + * a protection anyway. Also it's useful for WATCH. * - * - If dsSet() fails on the write thread log the error and reschedule the - * key for flush. + * Btw there is to check what happens when WATCH gets combined to keys + * that gets removed from the object cache. Should be save but better + * to check. * - * - Check why INCR will not update the LRU info for the object. + * - Check if/why INCR will not update the LRU info for the object. * * - Fix/Check the following race condition: a key gets a DEL so there is * a write operation scheduled against this key. Later the same key will @@ -105,6 +62,27 @@ * value so it will be evicted later. * * Are there other patterns like this where we load stale data? + * + * Also, make sure that key preloading is ONLY done for keys that are + * not marked as cacheKeyDoesNotExist(), otherwise, again, we can load + * data from disk that should instead be deleted. + * + * - dsSet() should use rename(2) in order to avoid corruptions. + * + * - Don't add a LOAD if there is already a LOADINPROGRESS, or is this + * impossible since anyway the io_keys stuff will work as lock? + * + * - Serialize special encoded things in a raw form. + * + * - When putting IO read operations on top of the queue, do this only if + * the already-on-top operation is not a save or if it is a save that + * is scheduled for later execution. If there is a save that is ready to + * fire, let's insert the load operation just before the first save that + * is scheduled for later exection for instance. + * + * - Support MULTI/EXEC transactions via a journal file, that is played on + * startup to check if there is cleanup to do. This way we can implement + * transactions with our simple file based KV store. */ /* Virtual Memory is composed mainly of two subsystems: @@ -129,6 +107,8 @@ */ void spawnIOThread(void); +int cacheScheduleIOPushJobs(int flags); +int processActiveIOJobs(int max); /* =================== Virtual Memory - Blocking Side ====================== */ @@ -152,6 +132,7 @@ void dsInit(void) { server.io_ready_clients = listCreate(); pthread_mutex_init(&server.io_mutex,NULL); pthread_cond_init(&server.io_condvar,NULL); + pthread_mutex_init(&server.bgsavethread_mutex,NULL); server.io_active_threads = 0; if (pipe(pipefds) == -1) { redisLog(REDIS_WARNING,"Unable to intialized DS: pipe(2): %s. Exiting." @@ -204,21 +185,21 @@ int cacheFreeOneEntry(void) { * are swappable objects */ int maxtries = 100; - if (dictSize(db->dict) == 0) continue; - for (i = 0; i < 5; i++) { + for (i = 0; i < 5 && dictSize(db->dict); i++) { dictEntry *de; double swappability; + robj keyobj; + sds keystr; if (maxtries) maxtries--; de = dictGetRandomKey(db->dict); + keystr = dictGetEntryKey(de); val = dictGetEntryVal(de); - /* Only swap objects that are currently in memory. - * - * Also don't swap shared objects: not a good idea in general and - * we need to ensure that the main thread does not touch the - * object while the I/O thread is using it, but we can't - * control other keys without adding additional mutex. */ - if (val->storage != REDIS_DS_MEMORY) { + initStaticStringObject(keyobj,keystr); + + /* Don't remove objects that are currently target of a + * read or write operation. */ + if (cacheScheduleIOGetFlags(db,&keyobj) != 0) { if (maxtries) i--; /* don't count this try */ continue; } @@ -231,10 +212,17 @@ int cacheFreeOneEntry(void) { } } if (best == NULL) { - /* FIXME: If there are objects marked as DS_DIRTY or DS_SAVING - * let's wait for this objects to be clear and retry... - * - * Object cache vm limit is considered an hard limit. */ + /* Was not able to fix a single object... we should check if our + * IO queues have stuff in queue, and try to consume the queue + * otherwise we'll use an infinite amount of memory if changes to + * the dataset are faster than I/O */ + if (listLength(server.cache_io_queue) > 0) { + redisLog(REDIS_DEBUG,"--- Busy waiting IO to reclaim memory"); + cacheScheduleIOPushJobs(REDIS_IO_ASAP); + processActiveIOJobs(1); + return REDIS_OK; + } + /* Nothing to free at all... */ return REDIS_ERR; } key = dictGetEntryKey(best); @@ -259,7 +247,72 @@ int dsCanTouchDiskStore(void) { return (server.bgsavechildpid == -1 && server.bgrewritechildpid == -1); } -/* =================== Virtual Memory - Threaded I/O ======================= */ +/* ==================== Disk store negative caching ======================== + * + * When disk store is enabled, we need negative caching, that is, to remember + * keys that are for sure *not* on the disk key-value store. + * + * This is usefuls because without negative caching cache misses will cost us + * a disk lookup, even if the same non existing key is accessed again and again. + * + * With negative caching we remember that the key is not on disk, so if it's + * not in memory and we have a negative cache entry, we don't try a disk + * access at all. + */ + +/* Returns true if the specified key may exists on disk, that is, we don't + * have an entry in our negative cache for this key */ +int cacheKeyMayExist(redisDb *db, robj *key) { + return dictFind(db->io_negcache,key) == NULL; +} + +/* Set the specified key as an entry that may possibily exist on disk, that is, + * remove the negative cache entry for this key if any. */ +void cacheSetKeyMayExist(redisDb *db, robj *key) { + dictDelete(db->io_negcache,key); +} + +/* Set the specified key as non existing on disk, that is, create a negative + * cache entry for this key. */ +void cacheSetKeyDoesNotExist(redisDb *db, robj *key) { + if (dictReplace(db->io_negcache,key,(void*)time(NULL))) { + incrRefCount(key); + } +} + +/* Remove one entry from negative cache using approximated LRU. */ +int negativeCacheEvictOneEntry(void) { + struct dictEntry *de; + robj *best = NULL; + redisDb *best_db = NULL; + time_t time, best_time = 0; + int j; + + for (j = 0; j < server.dbnum; j++) { + redisDb *db = server.db+j; + int i; + + if (dictSize(db->io_negcache) == 0) continue; + for (i = 0; i < 3; i++) { + de = dictGetRandomKey(db->io_negcache); + time = (time_t) dictGetEntryVal(de); + + if (best == NULL || time < best_time) { + best = dictGetEntryKey(de); + best_db = db; + best_time = time; + } + } + } + if (best) { + dictDelete(best_db->io_negcache,best); + return REDIS_OK; + } else { + return REDIS_ERR; + } +} + +/* ================== Disk store cache - Threaded I/O ====================== */ void freeIOJob(iojob *j) { decrRefCount(j->key); @@ -308,26 +361,32 @@ void vmThreadedIOCompletedJob(aeEventLoop *el, int fd, void *privdata, if (j->type == REDIS_IOJOB_LOAD) { /* Create the key-value pair in the in-memory database */ if (j->val != NULL) { - /* Note: the key may already be here if between the time - * this key loading was scheduled and now there was the - * need to blocking load the key for a key lookup. */ + /* Note: it's possible that the key is already in memory + * due to a blocking load operation. */ if (dbAdd(j->db,j->key,j->val) == REDIS_OK) { incrRefCount(j->val); if (j->expire != -1) setExpire(j->db,j->key,j->expire); } } else { - /* The key does not exist. Create a negative cache entry - * for this key. */ - /* FIXME: add this entry into the negative cache */ + /* Key not found on disk. If it is also not in memory + * as a cached object, nor there is a job writing it + * in background, we are sure the key does not exist + * currently. + * + * So we set a negative cache entry avoiding that the + * resumed client will block load what does not exist... */ + if (dictFind(j->db->dict,j->key->ptr) == NULL && + (cacheScheduleIOGetFlags(j->db,j->key) & + (REDIS_IO_SAVE|REDIS_IO_SAVEINPROG)) == 0) + { + cacheSetKeyDoesNotExist(j->db,j->key); + } } - /* Handle clients waiting for this key to be loaded. */ + cacheScheduleIODelFlag(j->db,j->key,REDIS_IO_LOADINPROG); handleClientsBlockedOnSwappedKey(j->db,j->key); freeIOJob(j); } else if (j->type == REDIS_IOJOB_SAVE) { - if (j->val) { - redisAssert(j->val->storage == REDIS_DS_SAVING); - j->val->storage = REDIS_DS_MEMORY; - } + cacheScheduleIODelFlag(j->db,j->key,REDIS_IO_SAVEINPROG); freeIOJob(j); } processed++; @@ -362,6 +421,8 @@ void *IOThreadEntryPoint(void *arg) { pthread_cond_wait(&server.io_condvar,&server.io_mutex); continue; } + redisLog(REDIS_DEBUG,"%ld IO jobs to process", + listLength(server.io_newjobs)); ln = listFirst(server.io_newjobs); j = ln->value; listDelNode(server.io_newjobs,ln); @@ -383,7 +444,6 @@ void *IOThreadEntryPoint(void *arg) { if (j->val) j->expire = expire; } else if (j->type == REDIS_IOJOB_SAVE) { if (j->val) { - redisAssert(j->val->storage == REDIS_DS_SAVING); dsSet(j->db,j->key,j->val); } else { dsDel(j->db,j->key); @@ -425,57 +485,86 @@ void spawnIOThread(void) { server.io_active_threads++; } -/* Wait that all the pending IO Jobs are processed */ -void waitEmptyIOJobsQueue(void) { - while(1) { +/* Wait that up to 'max' pending IO Jobs are processed by the I/O thread. + * From our point of view an IO job processed means that the count of + * server.io_processed must increase by one. + * + * If max is -1, all the pending IO jobs will be processed. + * + * Returns the number of IO jobs processed. + * + * NOTE: while this may appear like a busy loop, we are actually blocked + * by IO since we continuously acquire/release the IO lock. */ +int processActiveIOJobs(int max) { + int processed = 0; + + while(max == -1 || max > 0) { int io_processed_len; lockThreadedIO(); if (listLength(server.io_newjobs) == 0 && listLength(server.io_processing) == 0) { + /* There is nothing more to process */ unlockThreadedIO(); - return; + break; } + +#if 0 /* If there are new jobs we need to signal the thread to - * process the next one. */ + * process the next one. FIXME: drop this if useless. */ redisLog(REDIS_DEBUG,"waitEmptyIOJobsQueue: new %d, processing %d", listLength(server.io_newjobs), listLength(server.io_processing)); - /* + if (listLength(server.io_newjobs)) { pthread_cond_signal(&server.io_condvar); } - */ - /* While waiting for empty jobs queue condition we post-process some - * finshed job, as I/O threads may be hanging trying to write against - * the io_ready_pipe_write FD but there are so much pending jobs that - * it's blocking. */ +#endif + + /* Check if we can process some finished job */ io_processed_len = listLength(server.io_processed); unlockThreadedIO(); if (io_processed_len) { vmThreadedIOCompletedJob(NULL,server.io_ready_pipe_read, (void*)0xdeadbeef,0); - usleep(1000); /* 1 millisecond */ - } else { - usleep(10000); /* 10 milliseconds */ + processed++; + if (max != -1) max--; } } + return processed; } -/* Process all the IO Jobs already completed by threads but still waiting - * processing from the main thread. */ -void processAllPendingIOJobs(void) { - while(1) { +void waitEmptyIOJobsQueue(void) { + processActiveIOJobs(-1); +} + +/* Process up to 'max' IO Jobs already completed by threads but still waiting + * processing from the main thread. + * + * If max == -1 all the pending jobs are processed. + * + * The number of processed jobs is returned. */ +int processPendingIOJobs(int max) { + int processed = 0; + + while(max == -1 || max > 0) { int io_processed_len; lockThreadedIO(); io_processed_len = listLength(server.io_processed); unlockThreadedIO(); - if (io_processed_len == 0) return; + if (io_processed_len == 0) break; vmThreadedIOCompletedJob(NULL,server.io_ready_pipe_read, (void*)0xdeadbeef,0); + if (max != -1) max--; + processed++; } + return processed; +} + +void processAllPendingIOJobs(void) { + processPendingIOJobs(-1); } /* This function must be called while with threaded IO locked */ @@ -487,7 +576,21 @@ void queueIOJob(iojob *j) { spawnIOThread(); } -void dsCreateIOJob(int type, redisDb *db, robj *key, robj *val) { +/* Consume all the IO scheduled operations, and all the thread IO jobs + * so that eventually the state of diskstore is a point-in-time snapshot. + * + * This is useful when we need to BGSAVE with diskstore enabled. */ +void cacheForcePointInTime(void) { + redisLog(REDIS_NOTICE,"Diskstore: synching on disk to reach point-in-time state."); + while (listLength(server.cache_io_queue) != 0) { + cacheScheduleIOPushJobs(REDIS_IO_ASAP); + processActiveIOJobs(1); + } + waitEmptyIOJobsQueue(); + processAllPendingIOJobs(); +} + +void cacheCreateIOJob(int type, redisDb *db, robj *key, robj *val) { iojob *j; j = zmalloc(sizeof(*j)); @@ -504,94 +607,229 @@ void dsCreateIOJob(int type, redisDb *db, robj *key, robj *val) { unlockThreadedIO(); } -void cacheScheduleForFlush(redisDb *db, robj *key) { - dirtykey *dk; - dictEntry *de; - - de = dictFind(db->dict,key->ptr); - if (de) { - robj *val = dictGetEntryVal(de); - if (val->storage == REDIS_DS_DIRTY) - return; - else - val->storage = REDIS_DS_DIRTY; +/* ============= Disk store cache - Scheduling of IO operations ============= + * + * We use a queue and an hash table to hold the state of IO operations + * so that's fast to lookup if there is already an IO operation in queue + * for a given key. + * + * There are two types of IO operations for a given key: + * REDIS_IO_LOAD and REDIS_IO_SAVE. + * + * The function cacheScheduleIO() function pushes the specified IO operation + * in the queue, but avoid adding the same key for the same operation + * multiple times, thanks to the associated hash table. + * + * We take a set of flags per every key, so when the scheduled IO operation + * gets moved from the scheduled queue to the actual IO Jobs queue that + * is processed by the IO thread, we flag it as IO_LOADINPROG or + * IO_SAVEINPROG. + * + * So for every given key we always know if there is some IO operation + * scheduled, or in progress, for this key. + * + * NOTE: all this is very important in order to guarantee correctness of + * the Disk Store Cache. Jobs are always queued here. Load jobs are + * queued at the head for faster execution only in the case there is not + * already a write operation of some kind for this job. + * + * So we have ordering, but can do exceptions when there are no already + * operations for a given key. Also when we need to block load a given + * key, for an immediate lookup operation, we can check if the key can + * be accessed synchronously without race conditions (no IN PROGRESS + * operations for this key), otherwise we blocking wait for completion. */ + +#define REDIS_IO_LOAD 1 +#define REDIS_IO_SAVE 2 +#define REDIS_IO_LOADINPROG 4 +#define REDIS_IO_SAVEINPROG 8 + +void cacheScheduleIOAddFlag(redisDb *db, robj *key, long flag) { + struct dictEntry *de = dictFind(db->io_queued,key); + + if (!de) { + dictAdd(db->io_queued,key,(void*)flag); + incrRefCount(key); + return; + } else { + long flags = (long) dictGetEntryVal(de); + + if (flags & flag) { + redisLog(REDIS_WARNING,"Adding the same flag again: was: %ld, addede: %ld",flags,flag); + redisAssert(!(flags & flag)); + } + flags |= flag; + dictGetEntryVal(de) = (void*) flags; } +} + +void cacheScheduleIODelFlag(redisDb *db, robj *key, long flag) { + struct dictEntry *de = dictFind(db->io_queued,key); + long flags; - redisLog(REDIS_DEBUG,"Scheduling key %s for saving (%s)",key->ptr, - de ? "key exists" : "key does not exist"); - dk = zmalloc(sizeof(*dk)); - dk->db = db; - dk->key = key; + redisAssert(de != NULL); + flags = (long) dictGetEntryVal(de); + redisAssert(flags & flag); + flags &= ~flag; + if (flags == 0) { + dictDelete(db->io_queued,key); + } else { + dictGetEntryVal(de) = (void*) flags; + } +} + +int cacheScheduleIOGetFlags(redisDb *db, robj *key) { + struct dictEntry *de = dictFind(db->io_queued,key); + + return (de == NULL) ? 0 : ((long) dictGetEntryVal(de)); +} + +void cacheScheduleIO(redisDb *db, robj *key, int type) { + ioop *op; + long flags; + + if ((flags = cacheScheduleIOGetFlags(db,key)) & type) return; + + redisLog(REDIS_DEBUG,"Scheduling key %s for %s", + key->ptr, type == REDIS_IO_LOAD ? "loading" : "saving"); + cacheScheduleIOAddFlag(db,key,type); + op = zmalloc(sizeof(*op)); + op->type = type; + op->db = db; + op->key = key; incrRefCount(key); - dk->ctime = time(NULL); - listAddNodeTail(server.cache_flush_queue, dk); + op->ctime = time(NULL); + + /* Give priority to load operations if there are no save already + * in queue for the same key. */ + if (type == REDIS_IO_LOAD && !(flags & REDIS_IO_SAVE)) { + listAddNodeHead(server.cache_io_queue, op); + cacheScheduleIOPushJobs(REDIS_IO_ONLYLOADS); + } else { + /* FIXME: probably when this happens we want to at least move + * the write job about this queue on top, and set the creation time + * to a value that will force processing ASAP. */ + listAddNodeTail(server.cache_io_queue, op); + } } -void cacheCron(void) { +/* Push scheduled IO operations into IO Jobs that the IO thread can process. + * + * If flags include REDIS_IO_ONLYLOADS only load jobs are processed:this is + * useful since it's safe to push LOAD IO jobs from any place of the code, while + * SAVE io jobs should never be pushed while we are processing a command + * (not protected by lookupKey() that will block on keys in IO_SAVEINPROG + * state. + * + * The REDIS_IO_ASAP flag tells the function to don't wait for the IO job + * scheduled completion time, but just do the operation ASAP. This is useful + * when we need to reclaim memory from the IO queue. + */ +#define MAX_IO_JOBS_QUEUE 100 +int cacheScheduleIOPushJobs(int flags) { time_t now = time(NULL); listNode *ln; + int jobs, topush = 0, pushed = 0; + + /* Don't push new jobs if there is a threaded BGSAVE in progress. */ + if (server.bgsavethread != (pthread_t) -1) return 0; + + /* Sync stuff on disk, but only if we have less + * than MAX_IO_JOBS_QUEUE IO jobs. */ + lockThreadedIO(); + jobs = listLength(server.io_newjobs); + unlockThreadedIO(); + + topush = MAX_IO_JOBS_QUEUE-jobs; + if (topush < 0) topush = 0; + if (topush > (signed)listLength(server.cache_io_queue)) + topush = listLength(server.cache_io_queue); + + while((ln = listFirst(server.cache_io_queue)) != NULL) { + ioop *op = ln->value; + struct dictEntry *de; + robj *val; - /* Sync stuff on disk */ - while((ln = listFirst(server.cache_flush_queue)) != NULL) { - dirtykey *dk = ln->value; + if (!topush) break; + topush--; - if ((now - dk->ctime) >= server.cache_flush_delay) { - struct dictEntry *de; - robj *val; + if (op->type != REDIS_IO_LOAD && flags & REDIS_IO_ONLYLOADS) break; - redisLog(REDIS_DEBUG,"Creating IO Job to save key %s",dk->key->ptr); + /* Don't execute SAVE before the scheduled time for completion */ + if (op->type == REDIS_IO_SAVE && !(flags & REDIS_IO_ASAP) && + (now - op->ctime) < server.cache_flush_delay) break; + /* Don't add a SAVE job in the IO thread queue if there is already + * a save in progress for the same key. */ + if (op->type == REDIS_IO_SAVE && + cacheScheduleIOGetFlags(op->db,op->key) & REDIS_IO_SAVEINPROG) + { + /* Move the operation at the end of the list if there + * are other operations, so we can try to process the next one. + * Otherwise break, nothing to do here. */ + if (listLength(server.cache_io_queue) > 1) { + listDelNode(server.cache_io_queue,ln); + listAddNodeTail(server.cache_io_queue,op); + continue; + } else { + break; + } + } + + redisLog(REDIS_DEBUG,"Creating IO %s Job for key %s", + op->type == REDIS_IO_LOAD ? "load" : "save", op->key->ptr); + + if (op->type == REDIS_IO_LOAD) { + cacheCreateIOJob(REDIS_IOJOB_LOAD,op->db,op->key,NULL); + } else { /* Lookup the key, in order to put the current value in the IO - * Job and mark it as DS_SAVING. - * Otherwise if the key does not exists we schedule a disk store - * delete operation, setting the value to NULL. */ - de = dictFind(dk->db->dict,dk->key->ptr); + * Job. Otherwise if the key does not exists we schedule a disk + * store delete operation, setting the value to NULL. */ + de = dictFind(op->db->dict,op->key->ptr); if (de) { val = dictGetEntryVal(de); - redisAssert(val->storage == REDIS_DS_DIRTY); - val->storage = REDIS_DS_SAVING; } else { /* Setting the value to NULL tells the IO thread to delete * the key on disk. */ val = NULL; } - dsCreateIOJob(REDIS_IOJOB_SAVE,dk->db,dk->key,val); - listDelNode(server.cache_flush_queue,ln); - decrRefCount(dk->key); - zfree(dk); - } else { - break; /* too early */ + cacheCreateIOJob(REDIS_IOJOB_SAVE,op->db,op->key,val); } + /* Mark the operation as in progress. */ + cacheScheduleIODelFlag(op->db,op->key,op->type); + cacheScheduleIOAddFlag(op->db,op->key, + (op->type == REDIS_IO_LOAD) ? REDIS_IO_LOADINPROG : + REDIS_IO_SAVEINPROG); + /* Finally remove the operation from the queue. + * But we'll have trace of it in the hash table. */ + listDelNode(server.cache_io_queue,ln); + decrRefCount(op->key); + zfree(op); + pushed++; } + return pushed; +} + +void cacheCron(void) { + /* Push jobs */ + cacheScheduleIOPushJobs(0); /* Reclaim memory from the object cache */ while (server.ds_enabled && zmalloc_used_memory() > server.cache_max_memory) { - if (cacheFreeOneEntry() == REDIS_ERR) break; - } -} + int done = 0; -/* ============ Negative caching for diskstore objects ====================== */ -/* Since accesses to keys that don't exist with disk store cost us a disk - * access, we need to cache names of keys that do not exist but are frequently - * accessed. */ -int cacheKeyMayExist(redisDb *db, robj *key) { - /* FIXME: for now we just always return true. */ - return 1; + if (cacheFreeOneEntry() == REDIS_OK) done++; + if (negativeCacheEvictOneEntry() == REDIS_OK) done++; + if (done == 0) break; /* nothing more to free */ + } } -/* ============ Virtual Memory - Blocking clients on missing keys =========== */ +/* ========== Disk store cache - Blocking clients on missing keys =========== */ /* This function makes the clinet 'c' waiting for the key 'key' to be loaded. - * If the key is already in memory we don't need to block, regardless - * of the storage of the value object for this key: - * - * - If it's REDIS_DS_MEMORY we have the key in memory. - * - If it's REDIS_DS_DIRTY they key was modified, but still in memory. - * - if it's REDIS_DS_SAVING the key is being saved by an IO Job. When - * the client will lookup the key it will block if the key is still - * in this stage but it's more or less the best we can do. + * If the key is already in memory we don't need to block. * * FIXME: we should try if it's actually better to suspend the client * accessing an object that is being saved, and awake it only when @@ -611,6 +849,9 @@ int waitForSwappedKey(redisClient *c, robj *key) { de = dictFind(c->db->dict,key->ptr); if (de != NULL) return 0; + /* Don't wait for keys we are sure are not on disk either */ + if (!cacheKeyMayExist(c->db,key)) return 0; + /* Add the key to the list of keys this client is waiting for. * This maps clients to keys they are waiting for. */ listAddNodeTail(c->io_keys,key); @@ -632,15 +873,8 @@ int waitForSwappedKey(redisClient *c, robj *key) { listAddNodeTail(l,c); /* Are we already loading the key from disk? If not create a job */ - /* FIXME: if a given client was blocked for this key (so job already - * created) but the client was freed, there may be a job loading this - * key even if de == NULL. Does this creates some race condition? - * - * Example: after the first load the key gets a DEL that will schedule - * a write. But the write will happen later, the duplicated load will - * fire and we'll get again the key in memory. */ if (de == NULL) - dsCreateIOJob(REDIS_IOJOB_LOAD,c->db,key,NULL); + cacheScheduleIO(c->db,key,REDIS_IO_LOAD); return 1; }