maxmemory fixed, we now try to release memory just before we check for the memory...

[redis.git] / src / aof.c

#include "redis.h"

#include <signal.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/time.h>
#include <sys/resource.h>
#include <sys/wait.h>

/* Called when the user switches from "appendonly yes" to "appendonly no"
 * at runtime using the CONFIG command. */
void stopAppendOnly(void) {
    flushAppendOnlyFile();
    aof_fsync(server.appendfd);
    close(server.appendfd);

    server.appendfd = -1;
    server.appendseldb = -1;
    server.appendonly = 0;
    /* rewrite operation in progress? kill it, wait child exit */
    if (server.bgsavechildpid != -1) {
        int statloc;

        if (kill(server.bgsavechildpid,SIGKILL) != -1)
            wait3(&statloc,0,NULL);
        /* reset the buffer accumulating changes while the child saves */
        sdsfree(server.bgrewritebuf);
        server.bgrewritebuf = sdsempty();
        server.bgsavechildpid = -1;
    }
}

/* Called when the user switches from "appendonly no" to "appendonly yes"
 * at runtime using the CONFIG command. */
int startAppendOnly(void) {
    server.appendonly = 1;
    server.lastfsync = time(NULL);
    server.appendfd = open(server.appendfilename,O_WRONLY|O_APPEND|O_CREAT,0644);
    if (server.appendfd == -1) {
        redisLog(REDIS_WARNING,"Used tried to switch on AOF via CONFIG, but I can't open the AOF file: %s",strerror(errno));
        return REDIS_ERR;
    }
    if (rewriteAppendOnlyFileBackground() == REDIS_ERR) {
        server.appendonly = 0;
        close(server.appendfd);
        redisLog(REDIS_WARNING,"Used tried to switch on AOF via CONFIG, I can't trigger a background AOF rewrite operation. Check the above logs for more info about the error.",strerror(errno));
        return REDIS_ERR;
    }
    return REDIS_OK;
}

/* Write the append only file buffer on disk.
 *
 * Since we are required to write the AOF before replying to the client,
 * and the only way the client socket can get a write is entering when the
 * the event loop, we accumulate all the AOF writes in a memory
 * buffer and write it on disk using this function just before entering
 * the event loop again. */
void flushAppendOnlyFile(void) {
    time_t now;
    ssize_t nwritten;

    if (sdslen(server.aofbuf) == 0) return;

    /* We want to perform a single write. This should be guaranteed atomic
     * at least if the filesystem we are writing is a real physical one.
     * While this will save us against the server being killed I don't think
     * there is much to do about the whole server stopping for power problems
     * or alike */
     nwritten = write(server.appendfd,server.aofbuf,sdslen(server.aofbuf));
     if (nwritten != (signed)sdslen(server.aofbuf)) {
        /* Ooops, we are in troubles. The best thing to do for now is
         * aborting instead of giving the illusion that everything is
         * working as expected. */
         if (nwritten == -1) {
            redisLog(REDIS_WARNING,"Exiting on error writing to the append-only file: %s",strerror(errno));
         } else {
            redisLog(REDIS_WARNING,"Exiting on short write while writing to the append-only file: %s",strerror(errno));
         }
         exit(1);
    }
    sdsfree(server.aofbuf);
    server.aofbuf = sdsempty();

    /* Don't Fsync if no-appendfsync-on-rewrite is set to yes and we have
     * childs performing heavy I/O on disk. */
    if (server.no_appendfsync_on_rewrite &&
        (server.bgrewritechildpid != -1 || server.bgsavechildpid != -1))
            return;
    /* Fsync if needed */
    now = time(NULL);
    if (server.appendfsync == APPENDFSYNC_ALWAYS ||
        (server.appendfsync == APPENDFSYNC_EVERYSEC &&
         now-server.lastfsync > 1))
    {
        /* aof_fsync is defined as fdatasync() for Linux in order to avoid
         * flushing metadata. */
        aof_fsync(server.appendfd); /* Let's try to get this data on the disk */
        server.lastfsync = now;
    }
}

sds catAppendOnlyGenericCommand(sds buf, int argc, robj **argv) {
    int j;
    buf = sdscatprintf(buf,"*%d\r\n",argc);
    for (j = 0; j < argc; j++) {
        robj *o = getDecodedObject(argv[j]);
        buf = sdscatprintf(buf,"$%lu\r\n",(unsigned long)sdslen(o->ptr));
        buf = sdscatlen(buf,o->ptr,sdslen(o->ptr));
        buf = sdscatlen(buf,"\r\n",2);
        decrRefCount(o);
    }
    return buf;
}

sds catAppendOnlyExpireAtCommand(sds buf, robj *key, robj *seconds) {
    int argc = 3;
    long when;
    robj *argv[3];

    /* Make sure we can use strtol */
    seconds = getDecodedObject(seconds);
    when = time(NULL)+strtol(seconds->ptr,NULL,10);
    decrRefCount(seconds);

    argv[0] = createStringObject("EXPIREAT",8);
    argv[1] = key;
    argv[2] = createObject(REDIS_STRING,
        sdscatprintf(sdsempty(),"%ld",when));
    buf = catAppendOnlyGenericCommand(buf, argc, argv);
    decrRefCount(argv[0]);
    decrRefCount(argv[2]);
    return buf;
}

void feedAppendOnlyFile(struct redisCommand *cmd, int dictid, robj **argv, int argc) {
    sds buf = sdsempty();
    robj *tmpargv[3];

    /* The DB this command was targetting is not the same as the last command
     * we appendend. To issue a SELECT command is needed. */
    if (dictid != server.appendseldb) {
        char seldb[64];

        snprintf(seldb,sizeof(seldb),"%d",dictid);
        buf = sdscatprintf(buf,"*2\r\n$6\r\nSELECT\r\n$%lu\r\n%s\r\n",
            (unsigned long)strlen(seldb),seldb);
        server.appendseldb = dictid;
    }

    if (cmd->proc == expireCommand) {
        /* Translate EXPIRE into EXPIREAT */
        buf = catAppendOnlyExpireAtCommand(buf,argv[1],argv[2]);
    } else if (cmd->proc == setexCommand) {
        /* Translate SETEX to SET and EXPIREAT */
        tmpargv[0] = createStringObject("SET",3);
        tmpargv[1] = argv[1];
        tmpargv[2] = argv[3];
        buf = catAppendOnlyGenericCommand(buf,3,tmpargv);
        decrRefCount(tmpargv[0]);
        buf = catAppendOnlyExpireAtCommand(buf,argv[1],argv[2]);
    } else {
        buf = catAppendOnlyGenericCommand(buf,argc,argv);
    }

    /* Append to the AOF buffer. This will be flushed on disk just before
     * of re-entering the event loop, so before the client will get a
     * positive reply about the operation performed. */
    server.aofbuf = sdscatlen(server.aofbuf,buf,sdslen(buf));

    /* If a background append only file rewriting is in progress we want to
     * accumulate the differences between the child DB and the current one
     * in a buffer, so that when the child process will do its work we
     * can append the differences to the new append only file. */
    if (server.bgrewritechildpid != -1)
        server.bgrewritebuf = sdscatlen(server.bgrewritebuf,buf,sdslen(buf));

    sdsfree(buf);
}

/* In Redis commands are always executed in the context of a client, so in
 * order to load the append only file we need to create a fake client. */
struct redisClient *createFakeClient(void) {
    struct redisClient *c = zmalloc(sizeof(*c));

    selectDb(c,0);
    c->fd = -1;
    c->querybuf = sdsempty();
    c->argc = 0;
    c->argv = NULL;
    c->bufpos = 0;
    c->flags = 0;
    /* We set the fake client as a slave waiting for the synchronization
     * so that Redis will not try to send replies to this client. */
    c->replstate = REDIS_REPL_WAIT_BGSAVE_START;
    c->reply = listCreate();
    c->watched_keys = listCreate();
    listSetFreeMethod(c->reply,decrRefCount);
    listSetDupMethod(c->reply,dupClientReplyValue);
    initClientMultiState(c);
    return c;
}

void freeFakeClient(struct redisClient *c) {
    sdsfree(c->querybuf);
    listRelease(c->reply);
    listRelease(c->watched_keys);
    freeClientMultiState(c);
    zfree(c);
}

/* Replay the append log file. On error REDIS_OK is returned. On non fatal
 * error (the append only file is zero-length) REDIS_ERR is returned. On
 * fatal error an error message is logged and the program exists. */
int loadAppendOnlyFile(char *filename) {
    struct redisClient *fakeClient;
    FILE *fp = fopen(filename,"r");
    struct redis_stat sb;
    int appendonly = server.appendonly;

    if (redis_fstat(fileno(fp),&sb) != -1 && sb.st_size == 0)
        return REDIS_ERR;

    if (fp == NULL) {
        redisLog(REDIS_WARNING,"Fatal error: can't open the append log file for reading: %s",strerror(errno));
        exit(1);
    }

    /* Temporarily disable AOF, to prevent EXEC from feeding a MULTI
     * to the same file we're about to read. */
    server.appendonly = 0;

    fakeClient = createFakeClient();
    while(1) {
        int argc, j;
        unsigned long len;
        robj **argv;
        char buf[128];
        sds argsds;
        struct redisCommand *cmd;
        int force_swapout;

        if (fgets(buf,sizeof(buf),fp) == NULL) {
            if (feof(fp))
                break;
            else
                goto readerr;
        }
        if (buf[0] != '*') goto fmterr;
        argc = atoi(buf+1);
        argv = zmalloc(sizeof(robj*)*argc);
        for (j = 0; j < argc; j++) {
            if (fgets(buf,sizeof(buf),fp) == NULL) goto readerr;
            if (buf[0] != '$') goto fmterr;
            len = strtol(buf+1,NULL,10);
            argsds = sdsnewlen(NULL,len);
            if (len && fread(argsds,len,1,fp) == 0) goto fmterr;
            argv[j] = createObject(REDIS_STRING,argsds);
            if (fread(buf,2,1,fp) == 0) goto fmterr; /* discard CRLF */
        }

        /* Command lookup */
        cmd = lookupCommand(argv[0]->ptr);
        if (!cmd) {
            redisLog(REDIS_WARNING,"Unknown command '%s' reading the append only file", argv[0]->ptr);
            exit(1);
        }
        /* Try object encoding */
        if (cmd->flags & REDIS_CMD_BULK)
            argv[argc-1] = tryObjectEncoding(argv[argc-1]);
        /* Run the command in the context of a fake client */
        fakeClient->argc = argc;
        fakeClient->argv = argv;
        cmd->proc(fakeClient);

        /* The fake client should not have a reply */
        redisAssert(fakeClient->bufpos == 0 && listLength(fakeClient->reply) == 0);

        /* Clean up, ready for the next command */
        for (j = 0; j < argc; j++) decrRefCount(argv[j]);
        zfree(argv);

        /* Handle swapping while loading big datasets when VM is on */
        force_swapout = 0;
        if ((zmalloc_used_memory() - server.vm_max_memory) > 1024*1024*32)
            force_swapout = 1;

        if (server.vm_enabled && force_swapout) {
            while (zmalloc_used_memory() > server.vm_max_memory) {
                if (vmSwapOneObjectBlocking() == REDIS_ERR) break;
            }
        }
    }

    /* This point can only be reached when EOF is reached without errors.
     * If the client is in the middle of a MULTI/EXEC, log error and quit. */
    if (fakeClient->flags & REDIS_MULTI) goto readerr;

    fclose(fp);
    freeFakeClient(fakeClient);
    server.appendonly = appendonly;
    return REDIS_OK;

readerr:
    if (feof(fp)) {
        redisLog(REDIS_WARNING,"Unexpected end of file reading the append only file");
    } else {
        redisLog(REDIS_WARNING,"Unrecoverable error reading the append only file: %s", strerror(errno));
    }
    exit(1);
fmterr:
    redisLog(REDIS_WARNING,"Bad file format reading the append only file: make a backup of your AOF file, then use ./redis-check-aof --fix <filename>");
    exit(1);
}

/* Write binary-safe string into a file in the bulkformat
 * $<count>\r\n<payload>\r\n */
int fwriteBulkString(FILE *fp, char *s, unsigned long len) {
    char cbuf[128];
    int clen;
    cbuf[0] = '$';
    clen = 1+ll2string(cbuf+1,sizeof(cbuf)-1,len);
    cbuf[clen++] = '\r';
    cbuf[clen++] = '\n';
    if (fwrite(cbuf,clen,1,fp) == 0) return 0;
    if (len > 0 && fwrite(s,len,1,fp) == 0) return 0;
    if (fwrite("\r\n",2,1,fp) == 0) return 0;
    return 1;
}

/* Write a double value in bulk format $<count>\r\n<payload>\r\n */
int fwriteBulkDouble(FILE *fp, double d) {
    char buf[128], dbuf[128];

    snprintf(dbuf,sizeof(dbuf),"%.17g\r\n",d);
    snprintf(buf,sizeof(buf),"$%lu\r\n",(unsigned long)strlen(dbuf)-2);
    if (fwrite(buf,strlen(buf),1,fp) == 0) return 0;
    if (fwrite(dbuf,strlen(dbuf),1,fp) == 0) return 0;
    return 1;
}

/* Write a long value in bulk format $<count>\r\n<payload>\r\n */
int fwriteBulkLongLong(FILE *fp, long long l) {
    char bbuf[128], lbuf[128];
    unsigned int blen, llen;
    llen = ll2string(lbuf,32,l);
    blen = snprintf(bbuf,sizeof(bbuf),"$%u\r\n%s\r\n",llen,lbuf);
    if (fwrite(bbuf,blen,1,fp) == 0) return 0;
    return 1;
}

/* Delegate writing an object to writing a bulk string or bulk long long. */
int fwriteBulkObject(FILE *fp, robj *obj) {
    /* Avoid using getDecodedObject to help copy-on-write (we are often
     * in a child process when this function is called). */
    if (obj->encoding == REDIS_ENCODING_INT) {
        return fwriteBulkLongLong(fp,(long)obj->ptr);
    } else if (obj->encoding == REDIS_ENCODING_RAW) {
        return fwriteBulkString(fp,obj->ptr,sdslen(obj->ptr));
    } else {
        redisPanic("Unknown string encoding");
    }
}

/* Write a sequence of commands able to fully rebuild the dataset into
 * "filename". Used both by REWRITEAOF and BGREWRITEAOF. */
int rewriteAppendOnlyFile(char *filename) {
    dictIterator *di = NULL;
    dictEntry *de;
    FILE *fp;
    char tmpfile[256];
    int j;
    time_t now = time(NULL);

    /* Note that we have to use a different temp name here compared to the
     * one used by rewriteAppendOnlyFileBackground() function. */
    snprintf(tmpfile,256,"temp-rewriteaof-%d.aof", (int) getpid());
    fp = fopen(tmpfile,"w");
    if (!fp) {
        redisLog(REDIS_WARNING, "Failed rewriting the append only file: %s", strerror(errno));
        return REDIS_ERR;
    }
    for (j = 0; j < server.dbnum; j++) {
        char selectcmd[] = "*2\r\n$6\r\nSELECT\r\n";
        redisDb *db = server.db+j;
        dict *d = db->dict;
        if (dictSize(d) == 0) continue;
        di = dictGetIterator(d);
        if (!di) {
            fclose(fp);
            return REDIS_ERR;
        }

        /* SELECT the new DB */
        if (fwrite(selectcmd,sizeof(selectcmd)-1,1,fp) == 0) goto werr;
        if (fwriteBulkLongLong(fp,j) == 0) goto werr;

        /* Iterate this DB writing every entry */
        while((de = dictNext(di)) != NULL) {
            sds keystr = dictGetEntryKey(de);
            robj key, *o;
            time_t expiretime;
            int swapped;

            keystr = dictGetEntryKey(de);
            o = dictGetEntryVal(de);
            initStaticStringObject(key,keystr);
            /* If the value for this key is swapped, load a preview in memory.
             * We use a "swapped" flag to remember if we need to free the
             * value object instead to just increment the ref count anyway
             * in order to avoid copy-on-write of pages if we are forked() */
            if (!server.vm_enabled || o->storage == REDIS_VM_MEMORY ||
                o->storage == REDIS_VM_SWAPPING) {
                swapped = 0;
            } else {
                o = vmPreviewObject(o);
                swapped = 1;
            }
            expiretime = getExpire(db,&key);

            /* Save the key and associated value */
            if (o->type == REDIS_STRING) {
                /* Emit a SET command */
                char cmd[]="*3\r\n$3\r\nSET\r\n";
                if (fwrite(cmd,sizeof(cmd)-1,1,fp) == 0) goto werr;
                /* Key and value */
                if (fwriteBulkObject(fp,&key) == 0) goto werr;
                if (fwriteBulkObject(fp,o) == 0) goto werr;
            } else if (o->type == REDIS_LIST) {
                /* Emit the RPUSHes needed to rebuild the list */
                char cmd[]="*3\r\n$5\r\nRPUSH\r\n";
                if (o->encoding == REDIS_ENCODING_ZIPLIST) {
                    unsigned char *zl = o->ptr;
                    unsigned char *p = ziplistIndex(zl,0);
                    unsigned char *vstr;
                    unsigned int vlen;
                    long long vlong;

                    while(ziplistGet(p,&vstr,&vlen,&vlong)) {
                        if (fwrite(cmd,sizeof(cmd)-1,1,fp) == 0) goto werr;
                        if (fwriteBulkObject(fp,&key) == 0) goto werr;
                        if (vstr) {
                            if (fwriteBulkString(fp,(char*)vstr,vlen) == 0)
                                goto werr;
                        } else {
                            if (fwriteBulkLongLong(fp,vlong) == 0)
                                goto werr;
                        }
                        p = ziplistNext(zl,p);
                    }
                } else if (o->encoding == REDIS_ENCODING_LINKEDLIST) {
                    list *list = o->ptr;
                    listNode *ln;
                    listIter li;

                    listRewind(list,&li);
                    while((ln = listNext(&li))) {
                        robj *eleobj = listNodeValue(ln);

                        if (fwrite(cmd,sizeof(cmd)-1,1,fp) == 0) goto werr;
                        if (fwriteBulkObject(fp,&key) == 0) goto werr;
                        if (fwriteBulkObject(fp,eleobj) == 0) goto werr;
                    }
                } else {
                    redisPanic("Unknown list encoding");
                }
            } else if (o->type == REDIS_SET) {
                char cmd[]="*3\r\n$4\r\nSADD\r\n";

                /* Emit the SADDs needed to rebuild the set */
                if (o->encoding == REDIS_ENCODING_INTSET) {
                    int ii = 0;
                    int64_t llval;
                    while(intsetGet(o->ptr,ii++,&llval)) {
                        if (fwrite(cmd,sizeof(cmd)-1,1,fp) == 0) goto werr;
                        if (fwriteBulkObject(fp,&key) == 0) goto werr;
                        if (fwriteBulkLongLong(fp,llval) == 0) goto werr;
                    }
                } else if (o->encoding == REDIS_ENCODING_HT) {
                    dictIterator *di = dictGetIterator(o->ptr);
                    dictEntry *de;
                    while((de = dictNext(di)) != NULL) {
                        robj *eleobj = dictGetEntryKey(de);
                        if (fwrite(cmd,sizeof(cmd)-1,1,fp) == 0) goto werr;
                        if (fwriteBulkObject(fp,&key) == 0) goto werr;
                        if (fwriteBulkObject(fp,eleobj) == 0) goto werr;
                    }
                    dictReleaseIterator(di);
                } else {
                    redisPanic("Unknown set encoding");
                }
            } else if (o->type == REDIS_ZSET) {
                /* Emit the ZADDs needed to rebuild the sorted set */
                zset *zs = o->ptr;
                dictIterator *di = dictGetIterator(zs->dict);
                dictEntry *de;

                while((de = dictNext(di)) != NULL) {
                    char cmd[]="*4\r\n$4\r\nZADD\r\n";
                    robj *eleobj = dictGetEntryKey(de);
                    double *score = dictGetEntryVal(de);

                    if (fwrite(cmd,sizeof(cmd)-1,1,fp) == 0) goto werr;
                    if (fwriteBulkObject(fp,&key) == 0) goto werr;
                    if (fwriteBulkDouble(fp,*score) == 0) goto werr;
                    if (fwriteBulkObject(fp,eleobj) == 0) goto werr;
                }
                dictReleaseIterator(di);
            } else if (o->type == REDIS_HASH) {
                char cmd[]="*4\r\n$4\r\nHSET\r\n";

                /* Emit the HSETs needed to rebuild the hash */
                if (o->encoding == REDIS_ENCODING_ZIPMAP) {
                    unsigned char *p = zipmapRewind(o->ptr);
                    unsigned char *field, *val;
                    unsigned int flen, vlen;

                    while((p = zipmapNext(p,&field,&flen,&val,&vlen)) != NULL) {
                        if (fwrite(cmd,sizeof(cmd)-1,1,fp) == 0) goto werr;
                        if (fwriteBulkObject(fp,&key) == 0) goto werr;
                        if (fwriteBulkString(fp,(char*)field,flen) == 0)
                            goto werr;
                        if (fwriteBulkString(fp,(char*)val,vlen) == 0)
                            goto werr;
                    }
                } else {
                    dictIterator *di = dictGetIterator(o->ptr);
                    dictEntry *de;

                    while((de = dictNext(di)) != NULL) {
                        robj *field = dictGetEntryKey(de);
                        robj *val = dictGetEntryVal(de);

                        if (fwrite(cmd,sizeof(cmd)-1,1,fp) == 0) goto werr;
                        if (fwriteBulkObject(fp,&key) == 0) goto werr;
                        if (fwriteBulkObject(fp,field) == 0) goto werr;
                        if (fwriteBulkObject(fp,val) == 0) goto werr;
                    }
                    dictReleaseIterator(di);
                }
            } else {
                redisPanic("Unknown object type");
            }
            /* Save the expire time */
            if (expiretime != -1) {
                char cmd[]="*3\r\n$8\r\nEXPIREAT\r\n";
                /* If this key is already expired skip it */
                if (expiretime < now) continue;
                if (fwrite(cmd,sizeof(cmd)-1,1,fp) == 0) goto werr;
                if (fwriteBulkObject(fp,&key) == 0) goto werr;
                if (fwriteBulkLongLong(fp,expiretime) == 0) goto werr;
            }
            if (swapped) decrRefCount(o);
        }
        dictReleaseIterator(di);
    }

    /* Make sure data will not remain on the OS's output buffers */
    fflush(fp);
    aof_fsync(fileno(fp));
    fclose(fp);

    /* Use RENAME to make sure the DB file is changed atomically only
     * if the generate DB file is ok. */
    if (rename(tmpfile,filename) == -1) {
        redisLog(REDIS_WARNING,"Error moving temp append only file on the final destination: %s", strerror(errno));
        unlink(tmpfile);
        return REDIS_ERR;
    }
    redisLog(REDIS_NOTICE,"SYNC append only file rewrite performed");
    return REDIS_OK;

werr:
    fclose(fp);
    unlink(tmpfile);
    redisLog(REDIS_WARNING,"Write error writing append only file on disk: %s", strerror(errno));
    if (di) dictReleaseIterator(di);
    return REDIS_ERR;
}

/* This is how rewriting of the append only file in background works:
 *
 * 1) The user calls BGREWRITEAOF
 * 2) Redis calls this function, that forks():
 *    2a) the child rewrite the append only file in a temp file.
 *    2b) the parent accumulates differences in server.bgrewritebuf.
 * 3) When the child finished '2a' exists.
 * 4) The parent will trap the exit code, if it's OK, will append the
 *    data accumulated into server.bgrewritebuf into the temp file, and
 *    finally will rename(2) the temp file in the actual file name.
 *    The the new file is reopened as the new append only file. Profit!
 */
int rewriteAppendOnlyFileBackground(void) {
    pid_t childpid;

    if (server.bgrewritechildpid != -1) return REDIS_ERR;
    if (server.vm_enabled) waitEmptyIOJobsQueue();
    if ((childpid = fork()) == 0) {
        /* Child */
        char tmpfile[256];

        if (server.vm_enabled) vmReopenSwapFile();
        close(server.fd);
        snprintf(tmpfile,256,"temp-rewriteaof-bg-%d.aof", (int) getpid());
        if (rewriteAppendOnlyFile(tmpfile) == REDIS_OK) {
            _exit(0);
        } else {
            _exit(1);
        }
    } else {
        /* Parent */
        if (childpid == -1) {
            redisLog(REDIS_WARNING,
                "Can't rewrite append only file in background: fork: %s",
                strerror(errno));
            return REDIS_ERR;
        }
        redisLog(REDIS_NOTICE,
            "Background append only file rewriting started by pid %d",childpid);
        server.bgrewritechildpid = childpid;
        updateDictResizePolicy();
        /* We set appendseldb to -1 in order to force the next call to the
         * feedAppendOnlyFile() to issue a SELECT command, so the differences
         * accumulated by the parent into server.bgrewritebuf will start
         * with a SELECT statement and it will be safe to merge. */
        server.appendseldb = -1;
        return REDIS_OK;
    }
    return REDIS_OK; /* unreached */
}

void bgrewriteaofCommand(redisClient *c) {
    if (server.bgrewritechildpid != -1) {
        addReplyError(c,"Background append only file rewriting already in progress");
        return;
    }
    if (rewriteAppendOnlyFileBackground() == REDIS_OK) {
        addReplyStatus(c,"Background append only file rewriting started");
    } else {
        addReply(c,shared.err);
    }
}

void aofRemoveTempFile(pid_t childpid) {
    char tmpfile[256];

    snprintf(tmpfile,256,"temp-rewriteaof-bg-%d.aof", (int) childpid);
    unlink(tmpfile);
}

/* A background append only file rewriting (BGREWRITEAOF) terminated its work.
 * Handle this. */
void backgroundRewriteDoneHandler(int statloc) {
    int exitcode = WEXITSTATUS(statloc);
    int bysignal = WIFSIGNALED(statloc);

    if (!bysignal && exitcode == 0) {
        int fd;
        char tmpfile[256];

        redisLog(REDIS_NOTICE,
            "Background append only file rewriting terminated with success");
        /* Now it's time to flush the differences accumulated by the parent */
        snprintf(tmpfile,256,"temp-rewriteaof-bg-%d.aof", (int) server.bgrewritechildpid);
        fd = open(tmpfile,O_WRONLY|O_APPEND);
        if (fd == -1) {
            redisLog(REDIS_WARNING, "Not able to open the temp append only file produced by the child: %s", strerror(errno));
            goto cleanup;
        }
        /* Flush our data... */
        if (write(fd,server.bgrewritebuf,sdslen(server.bgrewritebuf)) !=
                (signed) sdslen(server.bgrewritebuf)) {
            redisLog(REDIS_WARNING, "Error or short write trying to flush the parent diff of the append log file in the child temp file: %s", strerror(errno));
            close(fd);
            goto cleanup;
        }
        redisLog(REDIS_NOTICE,"Parent diff flushed into the new append log file with success (%lu bytes)",sdslen(server.bgrewritebuf));
        /* Now our work is to rename the temp file into the stable file. And
         * switch the file descriptor used by the server for append only. */
        if (rename(tmpfile,server.appendfilename) == -1) {
            redisLog(REDIS_WARNING,"Can't rename the temp append only file into the stable one: %s", strerror(errno));
            close(fd);
            goto cleanup;
        }
        /* Mission completed... almost */
        redisLog(REDIS_NOTICE,"Append only file successfully rewritten.");
        if (server.appendfd != -1) {
            /* If append only is actually enabled... */
            close(server.appendfd);
            server.appendfd = fd;
            if (server.appendfsync != APPENDFSYNC_NO) aof_fsync(fd);
            server.appendseldb = -1; /* Make sure it will issue SELECT */
            redisLog(REDIS_NOTICE,"The new append only file was selected for future appends.");
        } else {
            /* If append only is disabled we just generate a dump in this
             * format. Why not? */
            close(fd);
        }
    } else if (!bysignal && exitcode != 0) {
        redisLog(REDIS_WARNING, "Background append only file rewriting error");
    } else {
        redisLog(REDIS_WARNING,
            "Background append only file rewriting terminated by signal %d",
            WTERMSIG(statloc));
    }
cleanup:
    sdsfree(server.bgrewritebuf);
    server.bgrewritebuf = sdsempty();
    aofRemoveTempFile(server.bgrewritechildpid);
    server.bgrewritechildpid = -1;
}