Lazyfree: ability to free whole DBs in background.

Author: antirez

src/bio.c

@@ -85,6 +85,8 @@ struct bio_job {
 
 void *bioProcessBackgroundJobs(void *arg);
 void lazyfreeFreeObjectFromBioThread(robj *o);
+void lazyfreeFreeDatabaseFromBioThread(dict *ht1, dict *ht2);
+void lazyfreeFreeSlotsMapFromBioThread(zskiplist *sl);
 
 /* Make sure we have enough stack to perform all the things we do in the
  * main thread. */
@@ -187,7 +189,16 @@ void *bioProcessBackgroundJobs(void *arg) {
         } else if (type == BIO_AOF_FSYNC) {
             aof_fsync((long)job->arg1);
         } else if (type == BIO_LAZY_FREE) {
-            lazyfreeFreeObjectFromBioThread(job->arg1);
+            /* What we free changes depending on what arguments are set:
+             * arg1 -> free the object at pointer.
+             * arg2 & arg3 -> free two dictionaries (a Redis DB).
+             * only arg3 -> free the skiplist. */
+            if (job->arg1)
+                lazyfreeFreeObjectFromBioThread(job->arg1);
+            else if (job->arg2 && job->arg3)
+                lazyfreeFreeDatabaseFromBioThread(job->arg2,job->arg3);
+            else if (job->arg3)
+                lazyfreeFreeSlotsMapFromBioThread(job->arg3);
         } else {
             serverPanic("Wrong job type in bioProcessBackgroundJobs().");
         }

src/cluster.c

@@ -495,7 +495,7 @@ void clusterReset(int hard) {
     if (nodeIsSlave(myself)) {
         clusterSetNodeAsMaster(myself);
         replicationUnsetMaster();
-        emptyDb(NULL);
+        emptyDb(-1,EMPTYDB_NO_FLAGS,NULL);
     }
 
     /* Close slots, reset manual failover state. */

src/db.c

@@ -29,6 +29,7 @@
 
 #include "server.h"
 #include "cluster.h"
+#include "atomicvar.h"
 
 #include <signal.h>
 #include <ctype.h>
@@ -238,16 +239,46 @@ robj *dbUnshareStringValue(redisDb *db, robj *key, robj *o) {
     return o;
 }
 
-long long emptyDb(void(callback)(void*)) {
-    int j;
+/* Remove all keys from all the databases in a Redis server.
+ * If callback is given the function is called from time to time to
+ * signal that work is in progress.
+ *
+ * The dbnum can be -1 if all teh DBs should be flushed, or the specified
+ * DB number if we want to flush only a single Redis database number.
+ *
+ * Flags are be EMPTYDB_NO_FLAGS if no special flags are specified or
+ * EMPTYDB_ASYCN if we want the memory to be freed in a different thread
+ * and the function to return ASAP.
+ *
+ * On success the fuction returns the number of keys removed from the
+ * database(s). Otherwise -1 is returned in the specific case the
+ * DB number is out of range, and errno is set to EINVAL. */
+long long emptyDb(int dbnum, int flags, void(callback)(void*)) {
+    int j, async = (flags & EMPTYDB_ASYNC);
     long long removed = 0;
 
+    if (dbnum < -1 || dbnum >= server.dbnum) {
+        errno = EINVAL;
+        return -1;
+    }
+
     for (j = 0; j < server.dbnum; j++) {
+        if (dbnum != 1 && dbnum != j) continue;
         removed += dictSize(server.db[j].dict);
-        dictEmpty(server.db[j].dict,callback);
-        dictEmpty(server.db[j].expires,callback);
+        if (async) {
+            emptyDbAsync(&server.db[j]);
+        } else {
+            dictEmpty(server.db[j].dict,callback);
+            dictEmpty(server.db[j].expires,callback);
+        }
+    }
+    if (server.cluster_enabled) {
+        if (async) {
+            slotToKeyFlushAsync();
+        } else {
+            slotToKeyFlush();
+        }
     }
-    if (server.cluster_enabled) slotToKeyFlush();
     return removed;
 }
 
@@ -290,7 +321,7 @@ void flushdbCommand(client *c) {
 
 void flushallCommand(client *c) {
     signalFlushedDb(-1);
-    server.dirty += emptyDb(NULL);
+    server.dirty += emptyDb(-1,EMPTYDB_NO_FLAGS,NULL);
     addReply(c,shared.ok);
     if (server.rdb_child_pid != -1) {
         kill(server.rdb_child_pid,SIGUSR1);

src/debug.c

@@ -271,15 +271,15 @@ void debugCommand(client *c) {
             addReply(c,shared.err);
             return;
         }
-        emptyDb(NULL);
+        emptyDb(-1,EMPTYDB_NO_FLAGS,NULL);
         if (rdbLoad(server.rdb_filename) != C_OK) {
             addReplyError(c,"Error trying to load the RDB dump");
             return;
         }
         serverLog(LL_WARNING,"DB reloaded by DEBUG RELOAD");
         addReply(c,shared.ok);
     } else if (!strcasecmp(c->argv[1]->ptr,"loadaof")) {
-        emptyDb(NULL);
+        emptyDb(-1,EMPTYDB_NO_FLAGS,NULL);
         if (loadAppendOnlyFile(server.aof_filename) != C_OK) {
             addReply(c,shared.err);
             return;

src/lazyfree.c

@@ -1,6 +1,7 @@
 #include "server.h"
 #include "bio.h"
 #include "atomicvar.h"
+#include "cluster.h"
 
 static size_t lazyfree_objects = 0;
 pthread_mutex_t lazyfree_objects_mutex = PTHREAD_MUTEX_INITIALIZER;
@@ -75,9 +76,51 @@ int dbAsyncDelete(redisDb *db, robj *key) {
     }
 }
 
-/* Implementation of function to release a single object called from the
- * lazyfree thread from bio.c. */
+/* Empty a Redis DB asynchronously. What the function does actually is to
+ * create a new empty set of hash tables and scheduling the old ones for
+ * lazy freeing. */
+void emptyDbAsync(redisDb *db) {
+    dict *oldht1 = db->dict, *oldht2 = db->expires;
+    db->dict = dictCreate(&dbDictType,NULL);
+    db->expires = dictCreate(&keyptrDictType,NULL);
+    atomicIncr(lazyfree_objects,dictSize(oldht1),
+        &lazyfree_objects_mutex);
+    bioCreateBackgroundJob(BIO_LAZY_FREE,NULL,oldht1,oldht2);
+}
+
+/* Empty the slots-keys map of Redis CLuster by creating a new empty one
+ * and scheduiling the old for lazy freeing. */
+void slotToKeyFlushAsync(void) {
+    zskiplist *oldsl = server.cluster->slots_to_keys;
+    server.cluster->slots_to_keys = zslCreate();
+    atomicIncr(lazyfree_objects,oldsl->length,
+        &lazyfree_objects_mutex);
+    bioCreateBackgroundJob(BIO_LAZY_FREE,NULL,NULL,oldsl);
+}
+
+/* Release objects from the lazyfree thread. It's just decrRefCount()
+ * updating the count of objects to release. */
 void lazyfreeFreeObjectFromBioThread(robj *o) {
     decrRefCount(o);
     atomicDecr(lazyfree_objects,1,&lazyfree_objects_mutex);
 }
+
+/* Release a database from the lazyfree thread. The 'db' pointer is the
+ * database which was substitutied with a fresh one in the main thread
+ * when the database was logically deleted. 'sl' is a skiplist used by
+ * Redis Cluster in order to take the hash slots -> keys mapping. This
+ * may be NULL if Redis Cluster is disabled. */
+void lazyfreeFreeDatabaseFromBioThread(dict *ht1, dict *ht2) {
+    size_t numkeys = dictSize(ht1);
+    dictRelease(ht1);
+    dictRelease(ht2);
+    atomicDecr(lazyfree_objects,numkeys,&lazyfree_objects_mutex);
+}
+
+/* Release the skiplist mapping Redis Cluster keys to slots in the
+ * lazyfree thread. */
+void lazyfreeFreeSlotsMapFromBioThread(zskiplist *sl) {
+    size_t len = sl->length;
+    zslFree(sl);
+    atomicDecr(lazyfree_objects,len,&lazyfree_objects_mutex);
+}

src/replication.c

@@ -1111,7 +1111,7 @@ void readSyncBulkPayload(aeEventLoop *el, int fd, void *privdata, int mask) {
         }
         serverLog(LL_NOTICE, "MASTER <-> SLAVE sync: Flushing old data");
         signalFlushedDb(-1);
-        emptyDb(replicationEmptyDbCallback);
+        emptyDb(-1,EMPTYDB_NO_FLAGS,replicationEmptyDbCallback);
         /* Before loading the DB into memory we need to delete the readable
          * handler, otherwise it will get called recursively since
          * rdbLoad() will call the event loop to process events from time to

src/server.h

@@ -1050,6 +1050,7 @@ extern dictType shaScriptObjectDictType;
 extern double R_Zero, R_PosInf, R_NegInf, R_Nan;
 extern dictType hashDictType;
 extern dictType replScriptCacheDictType;
+extern dictType keyptrDictType;
 
 /*-----------------------------------------------------------------------------
  * Functions prototypes
@@ -1384,7 +1385,11 @@ robj *dbRandomKey(redisDb *db);
 int dbSyncDelete(redisDb *db, robj *key);
 int dbDelete(redisDb *db, robj *key);
 robj *dbUnshareStringValue(redisDb *db, robj *key, robj *o);
-long long emptyDb(void(callback)(void*));
+
+#define EMPTYDB_NO_FLAGS 0      /* No flags. */
+#define EMPTYDB_ASYNC (1<<0)    /* Reclaim memory in another thread. */
+long long emptyDb(int dbnum, int flags, void(callback)(void*));
+
 int selectDb(client *c, int id);
 void signalModifiedKey(redisDb *db, robj *key);
 void signalFlushedDb(int dbid);
@@ -1407,6 +1412,8 @@ void slotToKeyFlush(void);
 #define LAZYFREE_STEP_OOM 2     /* Free a few elements at any cost if there
                                    is something to free: we are out of memory */
 int dbAsyncDelete(redisDb *db, robj *key);
+void emptyDbAsync(redisDb *db);
+void slotToKeyFlushAsync(void);
 
 /* API to get key arguments from commands */
 int *getKeysFromCommand(struct redisCommand *cmd, robj **argv, int argc, int *numkeys);