Refuse writes if can't persist on disk.

Redis now refuses accepting write queries if RDB persistence is
configured, but RDB snapshots can't be generated for some reason.
The status of the latest background save operation is now exposed
in the INFO output as well. This fixes issue #90.

src/rdb.c

@@ -656,6 +656,7 @@ int rdbSave(char *filename) {
     redisLog(REDIS_NOTICE,"DB saved on disk");
     server.dirty = 0;
     server.lastsave = time(NULL);
+    server.lastbgsave_status = REDIS_OK;
     return REDIS_OK;
 
 werr:
@@ -1061,12 +1062,15 @@ void backgroundSaveDoneHandler(int exitcode, int bysignal) {
             "Background saving terminated with success");
         server.dirty = server.dirty - server.dirty_before_bgsave;
         server.lastsave = time(NULL);
+        server.lastbgsave_status = REDIS_OK;
     } else if (!bysignal && exitcode != 0) {
         redisLog(REDIS_WARNING, "Background saving error");
+        server.lastbgsave_status = REDIS_ERR;
     } else {
         redisLog(REDIS_WARNING,
             "Background saving terminated by signal %d", bysignal);
         rdbRemoveTempFile(server.rdb_child_pid);
+        server.lastbgsave_status = REDIS_ERR;
     }
     server.rdb_child_pid = -1;
     /* Possibly there are slaves waiting for a BGSAVE in order to be served

src/redis.c

@@ -833,6 +833,8 @@ void createSharedObjects(void) {
         "-LOADING Redis is loading the dataset in memory\r\n"));
     shared.slowscripterr = createObject(REDIS_STRING,sdsnew(
         "-BUSY Redis is busy running a script. You can only call SCRIPT KILL or SHUTDOWN NOSAVE.\r\n"));
+    shared.bgsaveerr = createObject(REDIS_STRING,sdsnew(
+        "-MISCONF Redis is configured to save RDB snapshots, but is currently not able to persist on disk. Write commands are disabled. Please check Redis logs for details about the error.\r\n"));
     shared.space = createObject(REDIS_STRING,sdsnew(" "));
     shared.colon = createObject(REDIS_STRING,sdsnew(":"));
     shared.plus = createObject(REDIS_STRING,sdsnew("+"));
@@ -1088,6 +1090,7 @@ void initServer() {
     server.stat_fork_time = 0;
     server.stat_rejected_conn = 0;
     server.unixtime = time(NULL);
+    server.lastbgsave_status = REDIS_OK;
     aeCreateTimeEvent(server.el, 1, serverCron, NULL, NULL);
     if (server.ipfd > 0 && aeCreateFileEvent(server.el,server.ipfd,AE_READABLE,
         acceptTcpHandler,NULL) == AE_ERR) oom("creating file event");
@@ -1374,6 +1377,14 @@ int processCommand(redisClient *c) {
         }
     }
 
+    /* Don't accept write commands if there are problems persisting on disk. */
+    if (server.saveparamslen > 0 && server.lastbgsave_status == REDIS_ERR &&
+        c->cmd->flags & REDIS_CMD_WRITE)
+    {
+        addReply(c, shared.bgsaveerr);
+        return REDIS_OK;
+    }
+
     /* Only allow SUBSCRIBE and UNSUBSCRIBE in the context of Pub/Sub */
     if ((dictSize(c->pubsub_channels) > 0 || listLength(c->pubsub_patterns) > 0)
         &&
@@ -1645,12 +1656,14 @@ sds genRedisInfoString(char *section) {
             "changes_since_last_save:%lld\r\n"
             "bgsave_in_progress:%d\r\n"
             "last_save_time:%ld\r\n"
+            "last_bgsave_status:%s\r\n"
             "bgrewriteaof_in_progress:%d\r\n",
             server.loading,
             server.aof_state != REDIS_AOF_OFF,
             server.dirty,
             server.rdb_child_pid != -1,
             server.lastsave,
+            server.lastbgsave_status == REDIS_OK ? "ok" : "err",
             server.aof_child_pid != -1);
 
         if (server.aof_state != REDIS_AOF_OFF) {

src/redis.h

@@ -361,8 +361,8 @@ struct sharedObjectsStruct {
     robj *crlf, *ok, *err, *emptybulk, *czero, *cone, *cnegone, *pong, *space,
     *colon, *nullbulk, *nullmultibulk, *queued,
     *emptymultibulk, *wrongtypeerr, *nokeyerr, *syntaxerr, *sameobjecterr,
-    *outofrangeerr, *noscripterr, *loadingerr, *slowscripterr, *plus,
-    *select0, *select1, *select2, *select3, *select4,
+    *outofrangeerr, *noscripterr, *loadingerr, *slowscripterr, *bgsaveerr,
+    *plus, *select0, *select1, *select2, *select3, *select4,
     *select5, *select6, *select7, *select8, *select9,
     *messagebulk, *pmessagebulk, *subscribebulk, *unsubscribebulk,
     *psubscribebulk, *punsubscribebulk, *del, *rpop, *lpop,
@@ -567,6 +567,7 @@ struct redisServer {
     char *requirepass;          /* Pass for AUTH command, or NULL */
     char *pidfile;              /* PID file path */
     int arch_bits;              /* 32 or 64 depending on sizeof(long) */
+    int cronloops;              /* Number of times the cron function run */
     /* Networking */
     int port;                   /* TCP listening port */
     char *bindaddr;             /* Bind address or NULL */
@@ -587,8 +588,6 @@ struct redisServer {
     time_t loading_start_time;
     /* Fast pointers to often looked up command */
     struct redisCommand *delCommand, *multiCommand, *lpushCommand;
-    int cronloops;                  /* Number of times the cron function run */
-    time_t lastsave;                /* Unix time of last save succeeede */
     /* Fields used only for stats */
     time_t stat_starttime;          /* Server start time */
     long long stat_numcommands;     /* Number of processed commands */
@@ -636,6 +635,8 @@ struct redisServer {
     int saveparamslen;              /* Number of saving points */
     char *rdb_filename;             /* Name of RDB file */
     int rdb_compression;            /* Use compression in RDB? */
+    time_t lastsave;                /* Unix time of last save succeeede */
+    int lastbgsave_status;          /* REDIS_OK or REDIS_ERR */
     /* Propagation of commands in AOF / replication */
     redisOpArray also_propagate;    /* Additional command to propagate. */
     /* Logging */