void stopAppendOnly(void){
/*Called when the user switches from "appendonly yes" to "appendonly no"at runtime using the CONFIG command.*/
assert(server.aof_state == XREDIS_AOF_OFF);
/*force buffer contents to AOF file*/
flushAppendOnlyFile(1);
/*wait until disk writting is finished*/
aof_fsync(server.aof_fd);
/*set aof state*/
server.aof_fd = -1;
server.aof_selected_db = -1;
server.aof_state = XREDIS_AOF_OFF;
/*rewrite operation in progress? kill it, wait child exit*/
if(server.aof_child_pid != -1){
int statloc;
xredisLog(XREDIS_NOTICE, "killing running AOF rewrite child: %ld", (long)server.aof_child_pid);
if(kill(server.aof_child_pid, SIGKILL) != -1){
wait3(&statloc, 0, NULL);
}
/* reset the buffer accumulating changes while the child saves */
aofRewriteBufferReset(); //release rewrite buffer;
aofRemoveTempFile(server.aof_child_pid); //remove temp file;
/*change server state*/
server.aof_child_pid = -1;
server.aof_rewrite_time_start = -1;
}
}
//操作线程运行的函数。根据操作类型从任务队列中取出任务并调用相关函数执行
void *bioProcessBackgroundJobs(void *arg) {
struct bio_job *job;
unsigned long type = (unsigned long) arg;
sigset_t sigset;
/* Make the thread killable at any time, so that bioKillThreads()
* can work reliably. */
//设置属性使线程可以在任意时候被杀死
pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, NULL);
pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS, NULL);
pthread_mutex_lock(&bio_mutex[type]);
/* Block SIGALRM so we are sure that only the main thread will
* receive the watchdog signal. */
//阻塞信号量SIGALRM
sigemptyset(&sigset);
sigaddset(&sigset, SIGALRM);
if (pthread_sigmask(SIG_BLOCK, &sigset, NULL))
redisLog(REDIS_WARNING,
"Warning: can't mask SIGALRM in bio.c thread: %s", strerror(errno));
while(1) {
listNode *ln;
/* The loop always starts with the lock hold. */
//任务队列为空，等待新的任务的添加
if (listLength(bio_jobs[type]) == 0) {
//注意，wait的时候会将mutex释放，否则会有死锁
pthread_cond_wait(&bio_condvar[type],&bio_mutex[type]);
continue;
}
/* Pop the job from the queue. */
//从队列中取出一个任务
ln = listFirst(bio_jobs[type]);
job = ln->value;
/* It is now possible to unlock the background system as we know have
* a stand alone job structure to process.*/
//对bio_jobs操作结束，可以解锁
pthread_mutex_unlock(&bio_mutex[type]);
/* Process the job accordingly to its type. */
if (type == REDIS_BIO_CLOSE_FILE) {
//操作是close
close((long)job->arg1);
} else if (type == REDIS_BIO_AOF_FSYNC) {
//操作是fsync
aof_fsync((long)job->arg1);
} else {
redisPanic("Wrong job type in bioProcessBackgroundJobs().");
}
zfree(job);
/* Lock again before reiterating the loop, if there are no longer
* jobs to process we'll block again in pthread_cond_wait(). */
pthread_mutex_lock(&bio_mutex[type]);
//从队列删除执行完的任务，将pending值减1
listDelNode(bio_jobs[type],ln);
bio_pending[type]--;
}
}
/* A background append only file rewriting (BGREWRITEAOF) terminated its work.
* Handle this. */
void backgroundRewriteDoneHandler(int exitcode, int bysignal) {
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",
bysignal);
}
cleanup:
sdsfree(server.bgrewritebuf);
server.bgrewritebuf = sdsempty();
aofRemoveTempFile(server.bgrewritechildpid);
server.bgrewritechildpid = -1;
}
void *bioProcessBackgroundJobs(void *arg) {
struct bio_job *job;
unsigned long type = (unsigned long) arg;
sigset_t sigset;
/* Make the thread killable at any time, so that bioKillThreads()
* can work reliably. */
pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, NULL);
pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS, NULL);
pthread_mutex_lock(&bio_mutex[type]);
/* Block SIGALRM so we are sure that only the main thread will
* receive the watchdog signal. */
sigemptyset(&sigset);
sigaddset(&sigset, SIGALRM);
if (pthread_sigmask(SIG_BLOCK, &sigset, NULL))
serverLog(LL_WARNING,
"Warning: can't mask SIGALRM in bio.c thread: %s", strerror(errno));
while(1) {
listNode *ln;
/* The loop always starts with the lock hold. */
if (listLength(bio_jobs[type]) == 0) {
pthread_cond_wait(&bio_newjob_cond[type],&bio_mutex[type]);
continue;
}
/* Pop the job from the queue. */
ln = listFirst(bio_jobs[type]);
job = ln->value;
/* It is now possible to unlock the background system as we know have
* a stand alone job structure to process.*/
pthread_mutex_unlock(&bio_mutex[type]);
/* Process the job accordingly to its type. */
if (type == BIO_CLOSE_FILE) {
close((long)job->arg1);
} else if (type == BIO_AOF_FSYNC) {
aof_fsync((long)job->arg1);
} else {
serverPanic("Wrong job type in bioProcessBackgroundJobs().");
}
zfree(job);
/* Unblock threads blocked on bioWaitStepOfType() if any. */
pthread_cond_broadcast(&bio_step_cond[type]);
/* Lock again before reiterating the loop, if there are no longer
* jobs to process we'll block again in pthread_cond_wait(). */
pthread_mutex_lock(&bio_mutex[type]);
listDelNode(bio_jobs[type],ln);
bio_pending[type]--;
}
}
void *bioProcessBackgroundJobs(void *arg) {
struct bio_job *job;
#ifdef _WIN32
size_t type = (size_t) arg;
#else
unsigned long type = (unsigned long) arg;
#endif
sigset_t sigset;
pthread_detach(pthread_self());
pthread_mutex_lock(&bio_mutex[type]);
/* Block SIGALRM so we are sure that only the main thread will
* receive the watchdog signal. */
sigemptyset(&sigset);
sigaddset(&sigset, SIGALRM);
if (pthread_sigmask(SIG_BLOCK, &sigset, NULL))
redisLog(REDIS_WARNING,
"Warning: can't mask SIGALRM in bio.c thread: %s", strerror(errno));
while(1) {
listNode *ln;
/* The loop always starts with the lock hold. */
if (listLength(bio_jobs[type]) == 0) {
pthread_cond_wait(&bio_condvar[type],&bio_mutex[type]);
continue;
}
/* Pop the job from the queue. */
ln = listFirst(bio_jobs[type]);
job = ln->value;
/* It is now possible to unlock the background system as we know have
* a stand alone job structure to process.*/
pthread_mutex_unlock(&bio_mutex[type]);
/* Process the job accordingly to its type. */
if (type == REDIS_BIO_CLOSE_FILE) {
close((long)job->arg1);
} else if (type == REDIS_BIO_AOF_FSYNC) {
aof_fsync((long)job->arg1);
} else {
redisPanic("Wrong job type in bioProcessBackgroundJobs().");
}
zfree(job);
/* Lock again before reiterating the loop, if there are no longer
* jobs to process we'll block again in pthread_cond_wait(). */
pthread_mutex_lock(&bio_mutex[type]);
listDelNode(bio_jobs[type],ln);
bio_pending[type]--;
}
}
void *bioProcessBackgroundJobs(void *arg) {
//bioInit创建一个进程，用来刷文件。arg参数就是这个线程对应应该处理的任务号，用来索引bio_jobs[type]
struct bio_job *job;
unsigned long type = (unsigned long) arg;//实际上就是jobid。序号
sigset_t sigset;
pthread_detach(pthread_self());
pthread_mutex_lock(&bio_mutex[type]);//先锁一下，待会pthread_cond_wait
/* Block SIGALRM so we are sure that only the main thread will
* receive the watchdog signal. */
sigemptyset(&sigset);
sigaddset(&sigset, SIGALRM);
if (pthread_sigmask(SIG_BLOCK, &sigset, NULL))
redisLog(REDIS_WARNING, "Warning: can't mask SIGALRM in bio.c thread: %s", strerror(errno));
while(1) {
listNode *ln;
/* The loop always starts with the lock hold. */
if (listLength(bio_jobs[type]) == 0) {
//已经加锁了，进入等待bio_condvar[type]不为0，并立即解锁，等待。
//等其他线程pthread_cond_signal的时候，会通知这个线程，别等待了，从而再次加锁，返回。
pthread_cond_wait(&bio_condvar[type],&bio_mutex[type]);
continue;
}
/* Pop the job from the queue. */
ln = listFirst(bio_jobs[type]);//获取到了一个任务，处理值。
job = ln->value;
/* It is now possible to unlock the background system as we know have
* a stand alone job structure to process.*/
pthread_mutex_unlock(&bio_mutex[type]);
//根据不同的任务类型，做响应的清理。
/* Process the job accordingly to its type. */
if (type == REDIS_BIO_CLOSE_FILE) {
close((long)job->arg1);//关闭文件。
} else if (type == REDIS_BIO_AOF_FSYNC) {
aof_fsync((long)job->arg1);//同步刷新数据。
} else {
redisPanic("Wrong job type in bioProcessBackgroundJobs().");
}
zfree(job);
/* Lock again before reiterating the loop, if there are no longer
* jobs to process we'll block again in pthread_cond_wait(). */
pthread_mutex_lock(&bio_mutex[type]);
listDelNode(bio_jobs[type],ln);
bio_pending[type]--;//递减这种类型的挂起计数。
}
}
/* Returns 1 or 0 for success/failure. */
static size_t rioFileWrite(rio *r, const void *buf, size_t len) {
size_t retval;
retval = fwrite(buf,len,1,r->io.file.fp);
r->io.file.buffered += len;
if (r->io.file.autosync &&
r->io.file.buffered >= r->io.file.autosync)
{
aof_fsync(fileno(r->io.file.fp));
r->io.file.buffered = 0;
}
return retval;
}
/* Returns 1 or 0 for success/failure.
*
* 将长度为 len 的内容 buf 写入到文件 r 中。
*
* 成功返回 1 ，失败返回 0 。
*/
static size_t rioFileWrite(rio *r, const void *buf, size_t len)
{
size_t retval;
retval = fwrite(buf,len,1,r->io.file.fp);
r->io.file.buffered += len;
// 检查写入的字节数，看是否需要执行自动 sync
if (r->io.file.autosync &&
r->io.file.buffered >= r->io.file.autosync)
{
fflush(r->io.file.fp);
aof_fsync(fileno(r->io.file.fp));
r->io.file.buffered = 0;
}
return retval;
}
/* 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;
}
}
void *bioProcessBackgroundJobs(void *arg) {
struct bio_job *job;
#ifdef _WIN32
size_t type = (size_t) arg;
#else
unsigned long type = (unsigned long) arg;
#endif
pthread_detach(pthread_self());
pthread_mutex_lock(&bio_mutex[type]);
while(1) {
listNode *ln;
/* The loop always starts with the lock hold. */
if (listLength(bio_jobs[type]) == 0) {
pthread_cond_wait(&bio_condvar[type],&bio_mutex[type]);
continue;
}
/* Pop the job from the queue. */
ln = listFirst(bio_jobs[type]);
job = ln->value;
/* It is now possible to unlock the background system as we know have
* a stand alone job structure to process.*/
pthread_mutex_unlock(&bio_mutex[type]);
/* Process the job accordingly to its type. */
if (type == REDIS_BIO_CLOSE_FILE) {
close((long)(size_t)job->arg1);
} else if (type == REDIS_BIO_AOF_FSYNC) {
aof_fsync((long)(size_t)job->arg1);
} else {
redisPanic("Wrong job type in bioProcessBackgroundJobs().");
}
zfree(job);
/* Lock again before reiterating the loop, if there are no longer
* jobs to process we'll block again in pthread_cond_wait(). */
pthread_mutex_lock(&bio_mutex[type]);
listDelNode(bio_jobs[type],ln);
bio_pending[type]--;
}
}
/* Called when the user switches from "appendonly yes" to "appendonly no"
* at runtime using the CONFIG command. */
void stopAppendOnly(void) {
flushAppendOnlyFile(1);
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.bgrewritechildpid != -1) {
int statloc;
if (kill(server.bgrewritechildpid,SIGKILL) != -1)
wait3(&statloc,0,NULL);
/* reset the buffer accumulating changes while the child saves */
sdsfree(server.bgrewritebuf);
server.bgrewritebuf = sdsempty();
server.bgrewritechildpid = -1;
}
}
/* Called when the user switches from "appendonly yes" to "appendonly no"
* at runtime using the CONFIG command. */
void stopAppendOnly(void) {
redisAssert(server.aof_state != REDIS_AOF_OFF);
flushAppendOnlyFile(1);
aof_fsync(server.aof_fd);
close(server.aof_fd);
server.aof_fd = -1;
server.aof_selected_db = -1;
server.aof_state = REDIS_AOF_OFF;
/* rewrite operation in progress? kill it, wait child exit */
if (server.aof_child_pid != -1) {
int statloc;
redisLog(REDIS_NOTICE,"Killing running AOF rewrite child: %ld",
(long) server.aof_child_pid);
if (kill(server.aof_child_pid,SIGUSR1) != -1)
wait3(&statloc,0,NULL);
/* reset the buffer accumulating changes while the child saves */
aofRewriteBufferReset();
aofRemoveTempFile(server.aof_child_pid);
server.aof_child_pid = -1;
server.aof_rewrite_time_start = -1;
}
}
/* Write a sequence of commands able to fully rebuild the dataset into
* "filename". Used both by REWRITEAOF and BGREWRITEAOF.
*
* In order to minimize the number of commands needed in the rewritten
* log Redis uses variadic commands when possible, such as RPUSH, SADD
* and ZADD. However at max REDIS_AOF_REWRITE_ITEMS_PER_CMD items per time
* are inserted using a single command. */
int rewriteAppendOnlyFile(char *filename) {
dictIterator *di = NULL;
dictEntry *de;
rio aof;
FILE *fp;
char tmpfile[256];
int j;
long long now = mstime();
/* 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, "Opening the temp file for AOF rewrite in rewriteAppendOnlyFile(): %s", strerror(errno));
return REDIS_ERR;
}
rioInitWithFile(&aof,fp);
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 = dictGetSafeIterator(d);
if (!di) {
fclose(fp);
return REDIS_ERR;
}
/* SELECT the new DB */
if (rioWrite(&aof,selectcmd,sizeof(selectcmd)-1) == 0) goto werr;
if (rioWriteBulkLongLong(&aof,j) == 0) goto werr;
/* Iterate this DB writing every entry */
while((de = dictNext(di)) != NULL) {
sds keystr;
robj key, *o;
long long expiretime;
keystr = dictGetKey(de);
o = dictGetVal(de);
initStaticStringObject(key,keystr);
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 (rioWrite(&aof,cmd,sizeof(cmd)-1) == 0) goto werr;
/* Key and value */
if (rioWriteBulkObject(&aof,&key) == 0) goto werr;
if (rioWriteBulkObject(&aof,o) == 0) goto werr;
} else if (o->type == REDIS_LIST) {
if (rewriteListObject(&aof,&key,o) == 0) goto werr;
} else if (o->type == REDIS_SET) {
if (rewriteSetObject(&aof,&key,o) == 0) goto werr;
} else if (o->type == REDIS_ZSET) {
if (rewriteSortedSetObject(&aof,&key,o) == 0) goto werr;
} else if (o->type == REDIS_HASH) {
if (rewriteHashObject(&aof,&key,o) == 0) goto werr;
} else {
redisPanic("Unknown object type");
}
/* Save the expire time */
if (expiretime != -1) {
char cmd[]="*3\r\n$9\r\nPEXPIREAT\r\n";
/* If this key is already expired skip it */
if (expiretime < now) continue;
if (rioWrite(&aof,cmd,sizeof(cmd)-1) == 0) goto werr;
if (rioWriteBulkObject(&aof,&key) == 0) goto werr;
if (rioWriteBulkLongLong(&aof,expiretime) == 0) goto werr;
}
}
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;
}
/* 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.
*
* About the 'force' argument:
*
* When the fsync policy is set to 'everysec' we may delay the flush if there
* is still an fsync() going on in the background thread, since for instance
* on Linux write(2) will be blocked by the background fsync anyway.
* When this happens we remember that there is some aof buffer to be
* flushed ASAP, and will try to do that in the serverCron() function.
*
* However if force is set to 1 we'll write regardless of the background
* fsync. */
void flushAppendOnlyFile(int force) {
ssize_t nwritten;
int sync_in_progress = 0;
if (sdslen(server.aof_buf) == 0) return;
if (server.aof_fsync == AOF_FSYNC_EVERYSEC)
sync_in_progress = bioPendingJobsOfType(REDIS_BIO_AOF_FSYNC) != 0;
if (server.aof_fsync == AOF_FSYNC_EVERYSEC && !force) {
/* With this append fsync policy we do background fsyncing.
* If the fsync is still in progress we can try to delay
* the write for a couple of seconds. */
if (sync_in_progress) {
if (server.aof_flush_postponed_start == 0) {
/* No previous write postponinig, remember that we are
* postponing the flush and return. */
server.aof_flush_postponed_start = server.unixtime;
return;
} else if (server.unixtime - server.aof_flush_postponed_start < 2) {
/* We were already waiting for fsync to finish, but for less
* than two seconds this is still ok. Postpone again. */
return;
}
/* Otherwise fall trough, and go write since we can't wait
* over two seconds. */
server.aof_delayed_fsync++;
redisLog(REDIS_NOTICE,"Asynchronous AOF fsync is taking too long (disk is busy?). Writing the AOF buffer without waiting for fsync to complete, this may slow down Redis.");
}
}
/* If you are following this code path, then we are going to write so
* set reset the postponed flush sentinel to zero. */
server.aof_flush_postponed_start = 0;
/* 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.aof_fd,server.aof_buf,sdslen(server.aof_buf));
if (nwritten != (signed)sdslen(server.aof_buf)) {
/* 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 (nwritten=%ld, "
"expected=%ld)",
strerror(errno),
(long)nwritten,
(long)sdslen(server.aof_buf));
if (ftruncate(server.aof_fd, server.aof_current_size) == -1) {
redisLog(REDIS_WARNING, "Could not remove short write "
"from the append-only file. Redis may refuse "
"to load the AOF the next time it starts. "
"ftruncate: %s", strerror(errno));
}
}
exit(1);
}
server.aof_current_size += nwritten;
/* Re-use AOF buffer when it is small enough. The maximum comes from the
* arena size of 4k minus some overhead (but is otherwise arbitrary). */
if ((sdslen(server.aof_buf)+sdsavail(server.aof_buf)) < 4000) {
sdsclear(server.aof_buf);
} else {
sdsfree(server.aof_buf);
server.aof_buf = sdsempty();
}
/* Don't fsync if no-appendfsync-on-rewrite is set to yes and there are
* children doing I/O in the background. */
if (server.aof_no_fsync_on_rewrite &&
(server.aof_child_pid != -1 || server.rdb_child_pid != -1))
return;
/* Perform the fsync if needed. */
if (server.aof_fsync == AOF_FSYNC_ALWAYS) {
/* aof_fsync is defined as fdatasync() for Linux in order to avoid
* flushing metadata. */
aof_fsync(server.aof_fd); /* Let's try to get this data on the disk */
server.aof_last_fsync = server.unixtime;
} else if ((server.aof_fsync == AOF_FSYNC_EVERYSEC &&
server.unixtime > server.aof_last_fsync)) {
if (!sync_in_progress) aof_background_fsync(server.aof_fd);
server.aof_last_fsync = server.unixtime;
}
}
/* A background append only file rewriting (BGREWRITEAOF) terminated its work.
* Handle this. */
void backgroundRewriteDoneHandler(int exitcode, int bysignal) {
if (!bysignal && exitcode == 0) {
int newfd, oldfd;
char tmpfile[256];
long long now = ustime();
redisLog(REDIS_NOTICE,
"Background AOF rewrite terminated with success");
/* Flush the differences accumulated by the parent to the
* rewritten AOF. */
snprintf(tmpfile,256,"temp-rewriteaof-bg-%d.aof",
(int)server.aof_child_pid);
newfd = open(tmpfile,O_WRONLY|O_APPEND);
if (newfd == -1) {
redisLog(REDIS_WARNING,
"Unable to open the temporary AOF produced by the child: %s", strerror(errno));
goto cleanup;
}
if (aofRewriteBufferWrite(newfd) == -1) {
redisLog(REDIS_WARNING,
"Error trying to flush the parent diff to the rewritten AOF: %s", strerror(errno));
close(newfd);
goto cleanup;
}
redisLog(REDIS_NOTICE,
"Parent diff successfully flushed to the rewritten AOF (%lu bytes)", aofRewriteBufferSize());
/* The only remaining thing to do is to rename the temporary file to
* the configured file and switch the file descriptor used to do AOF
* writes. We don't want close(2) or rename(2) calls to block the
* server on old file deletion.
*
* There are two possible scenarios:
*
* 1) AOF is DISABLED and this was a one time rewrite. The temporary
* file will be renamed to the configured file. When this file already
* exists, it will be unlinked, which may block the server.
*
* 2) AOF is ENABLED and the rewritten AOF will immediately start
* receiving writes. After the temporary file is renamed to the
* configured file, the original AOF file descriptor will be closed.
* Since this will be the last reference to that file, closing it
* causes the underlying file to be unlinked, which may block the
* server.
*
* To mitigate the blocking effect of the unlink operation (either
* caused by rename(2) in scenario 1, or by close(2) in scenario 2), we
* use a background thread to take care of this. First, we
* make scenario 1 identical to scenario 2 by opening the target file
* when it exists. The unlink operation after the rename(2) will then
* be executed upon calling close(2) for its descriptor. Everything to
* guarantee atomicity for this switch has already happened by then, so
* we don't care what the outcome or duration of that close operation
* is, as long as the file descriptor is released again. */
if (server.aof_fd == -1) {
/* AOF disabled */
/* Don't care if this fails: oldfd will be -1 and we handle that.
* One notable case of -1 return is if the old file does
* not exist. */
oldfd = open(server.aof_filename,O_RDONLY|O_NONBLOCK);
} else {
/* AOF enabled */
oldfd = -1; /* We'll set this to the current AOF filedes later. */
}
/* Rename the temporary file. This will not unlink the target file if
* it exists, because we reference it with "oldfd". */
if (rename(tmpfile,server.aof_filename) == -1) {
redisLog(REDIS_WARNING,
"Error trying to rename the temporary AOF file: %s", strerror(errno));
close(newfd);
if (oldfd != -1) close(oldfd);
goto cleanup;
}
if (server.aof_fd == -1) {
/* AOF disabled, we don't need to set the AOF file descriptor
* to this new file, so we can close it. */
close(newfd);
} else {
/* AOF enabled, replace the old fd with the new one. */
oldfd = server.aof_fd;
server.aof_fd = newfd;
if (server.aof_fsync == AOF_FSYNC_ALWAYS)
aof_fsync(newfd);
else if (server.aof_fsync == AOF_FSYNC_EVERYSEC)
aof_background_fsync(newfd);
server.aof_selected_db = -1; /* Make sure SELECT is re-issued */
aofUpdateCurrentSize();
server.aof_rewrite_base_size = server.aof_current_size;
/* Clear regular AOF buffer since its contents was just written to
* the new AOF from the background rewrite buffer. */
sdsfree(server.aof_buf);
server.aof_buf = sdsempty();
}
server.aof_lastbgrewrite_status = REDIS_OK;
redisLog(REDIS_NOTICE, "Background AOF rewrite finished successfully");
/* Change state from WAIT_REWRITE to ON if needed */
if (server.aof_state == REDIS_AOF_WAIT_REWRITE)
server.aof_state = REDIS_AOF_ON;
/* Asynchronously close the overwritten AOF. */
if (oldfd != -1) bioCreateBackgroundJob(REDIS_BIO_CLOSE_FILE,(void*)(long)oldfd,NULL,NULL);
redisLog(REDIS_VERBOSE,
"Background AOF rewrite signal handler took %lldus", ustime()-now);
} else if (!bysignal && exitcode != 0) {
server.aof_lastbgrewrite_status = REDIS_ERR;
redisLog(REDIS_WARNING,
"Background AOF rewrite terminated with error");
} else {
server.aof_lastbgrewrite_status = REDIS_ERR;
redisLog(REDIS_WARNING,
"Background AOF rewrite terminated by signal %d", bysignal);
}
cleanup:
aofRewriteBufferReset();
aofRemoveTempFile(server.aof_child_pid);
server.aof_child_pid = -1;
server.aof_rewrite_time_last = time(NULL)-server.aof_rewrite_time_start;
server.aof_rewrite_time_start = -1;
/* Schedule a new rewrite if we are waiting for it to switch the AOF ON. */
if (server.aof_state == REDIS_AOF_WAIT_REWRITE)
server.aof_rewrite_scheduled = 1;
}
/* 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 = dictGetSafeIterator(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 */
char cmd[]="*4\r\n$4\r\nZADD\r\n";
if (o->encoding == REDIS_ENCODING_ZIPLIST) {
unsigned char *zl = o->ptr;
unsigned char *eptr, *sptr;
unsigned char *vstr;
unsigned int vlen;
long long vll;
double score;
eptr = ziplistIndex(zl,0);
redisAssert(eptr != NULL);
sptr = ziplistNext(zl,eptr);
redisAssert(sptr != NULL);
while (eptr != NULL) {
redisAssert(ziplistGet(eptr,&vstr,&vlen,&vll));
score = zzlGetScore(sptr);
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 (vstr != NULL) {
if (fwriteBulkString(fp,(char*)vstr,vlen) == 0)
goto werr;
} else {
if (fwriteBulkLongLong(fp,vll) == 0)
goto werr;
}
zzlNext(zl,&eptr,&sptr);
}
} else if (o->encoding == REDIS_ENCODING_SKIPLIST) {
zset *zs = o->ptr;
dictIterator *di = dictGetIterator(zs->dict);
dictEntry *de;
while((de = dictNext(di)) != NULL) {
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 {
redisPanic("Unknown sorted set encoding");
}
} 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;
}
void *bioProcessBackgroundJobs(void *arg) {
struct bio_job *job;
unsigned long type = (unsigned long) arg;
sigset_t sigset;
/* Make the thread killable at any time, so that bioKillThreads()
* can work reliably. */
/**
pthread_setcancelstate()函数用来设置当前线程的“可取消性”状态，并且将先前的状态返回到oldstate引用中。
“可取消性”状态的合法值分别是：PTHREAD_CANCEL_ENABLE 和 PTHREAD_CANCEL_DISABLE。
这个函数还可以查询当前线程的“可取消性”状态，即把第一个参数设为NULL。
*/
pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, NULL);
/**
pthread_setcanceltype() 函数用来设置当前线程的“可取消类型”，并且将先前的类型返回到oldtype引用中。
“可取消类型”的合法值分别是：
PTHREAD_CANCEL_DEFERRED ：线程接收到取消操作后，直到运行到“可取消点”后取消。
PTHREAD_CANCEL_ASYNCHRONOUS ：线程接收到取消操作后，立即取消。
*/
pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS, NULL);
pthread_mutex_lock(&bio_mutex[type]);
/* Block SIGALRM so we are sure that only the main thread will
* receive the watchdog signal. */
sigemptyset(&sigset);
sigaddset(&sigset, SIGALRM);
/**
在多线程的程序里，希望只在主线程中处理信号，可以使用
函数：
int pthread_sigmask (int how,
const sigset_t *set,
sigset_t *oset)
用作在主调线程里控制信号掩码。
How:
SIG_BLOCK: 结果集是当前集合参数集的并集
SIG_UNBLOCK: 结果集是当前集合参数集的差集
SIG_SETMASK: 结果集是由参数集指向的集
*/
if (pthread_sigmask(SIG_BLOCK, &sigset, NULL))
redisLog(REDIS_WARNING,
"Warning: can't mask SIGALRM in bio.c thread: %s", strerror(errno));
while(1) {
listNode *ln;
/* The loop always starts with the lock hold. */
if (listLength(bio_jobs[type]) == 0) {
/**
条件变量是利用线程间共享的全局变量进行同步的一种机制，主要包括两个动作：一个线程等待"条件变量的条件成立"而挂起；另一个线程使"条件成立"（给出条件成立信号）。
为了防止竞争，条件变量的使用总是和一个互斥锁结合在一起。
*/
pthread_cond_wait(&bio_condvar[type],&bio_mutex[type]);
continue;
}
/* Pop the job from the queue. */
ln = listFirst(bio_jobs[type]);
job = ln->value;
/* It is now possible to unlock the background system as we know have
* a stand alone job structure to process.*/
pthread_mutex_unlock(&bio_mutex[type]);
/* Process the job accordingly to its type. */
if (type == REDIS_BIO_CLOSE_FILE) {
close((long)job->arg1);
} else if (type == REDIS_BIO_AOF_FSYNC) {
aof_fsync((long)job->arg1);
} else {
redisPanic("Wrong job type in bioProcessBackgroundJobs().");
}
zfree(job);
/* Lock again before reiterating the loop, if there are no longer
* jobs to process we'll block again in pthread_cond_wait(). */
pthread_mutex_lock(&bio_mutex[type]);
listDelNode(bio_jobs[type],ln);
bio_pending[type]--;
}
}
/* 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.
*
* About the 'force' argument:
*
* When the fsync policy is set to 'everysec' we may delay the flush if there
* is still an fsync() going on in the background thread, since for instance
* on Linux write(2) will be blocked by the background fsync anyway.
* When this happens we remember that there is some aof buffer to be
* flushed ASAP, and will try to do that in the serverCron() function.
*
* However if force is set to 1 we'll write regardless of the background
* fsync. */
#define AOF_WRITE_LOG_ERROR_RATE 30 /* Seconds between errors logging. */
void flushAppendOnlyFile(int force) {
ssize_t nwritten;
int sync_in_progress = 0;
if (sdslen(server.aof_buf) == 0) return;
if (server.aof_fsync == AOF_FSYNC_EVERYSEC)
sync_in_progress = bioPendingJobsOfType(REDIS_BIO_AOF_FSYNC) != 0;
if (server.aof_fsync == AOF_FSYNC_EVERYSEC && !force) {
/* With this append fsync policy we do background fsyncing.
* If the fsync is still in progress we can try to delay
* the write for a couple of seconds. */
if (sync_in_progress) {
if (server.aof_flush_postponed_start == 0) {
/* No previous write postponinig, remember that we are
* postponing the flush and return. */
server.aof_flush_postponed_start = server.unixtime;
return;
} else if (server.unixtime - server.aof_flush_postponed_start < 2) {
/* We were already waiting for fsync to finish, but for less
* than two seconds this is still ok. Postpone again. */
return;
}
/* Otherwise fall trough, and go write since we can't wait
* over two seconds. */
server.aof_delayed_fsync++;
redisLog(REDIS_NOTICE,"Asynchronous AOF fsync is taking too long (disk is busy?). Writing the AOF buffer without waiting for fsync to complete, this may slow down Redis.");
}
}
/* If you are following this code path, then we are going to write so
* set reset the postponed flush sentinel to zero. */
server.aof_flush_postponed_start = 0;
/* 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.aof_fd,server.aof_buf,sdslen(server.aof_buf));
if (nwritten != (signed)sdslen(server.aof_buf)) {
static time_t last_write_error_log = 0;
int can_log = 0;
/* Limit logging rate to 1 line per AOF_WRITE_LOG_ERROR_RATE seconds. */
if ((server.unixtime - last_write_error_log) > AOF_WRITE_LOG_ERROR_RATE) {
can_log = 1;
last_write_error_log = server.unixtime;
}
/* Lof the AOF write error and record the error code. */
if (nwritten == -1) {
if (can_log) {
redisLog(REDIS_WARNING,"Error writing to the AOF file: %s",
strerror(errno));
server.aof_last_write_errno = errno;
}
} else {
if (can_log) {
redisLog(REDIS_WARNING,"Short write while writing to "
"the AOF file: (nwritten=%lld, "
"expected=%lld)",
(long long)nwritten,
(long long)sdslen(server.aof_buf));
}
if (ftruncate(server.aof_fd, server.aof_current_size) == -1) {
if (can_log) {
redisLog(REDIS_WARNING, "Could not remove short write "
"from the append-only file. Redis may refuse "
"to load the AOF the next time it starts. "
"ftruncate: %s", strerror(errno));
}
} else {
/* If the ftrunacate() succeeded we can set nwritten to
* -1 since there is no longer partial data into the AOF. */
nwritten = -1;
}
server.aof_last_write_errno = ENOSPC;
}
/* Handle the AOF write error. */
if (server.aof_fsync == AOF_FSYNC_ALWAYS) {
/* We can't recover when the fsync policy is ALWAYS since the
* reply for the client is already in the output buffers, and we
* have the contract with the user that on acknowledged write data
* is synched on disk. */
redisLog(REDIS_WARNING,"Can't recover from AOF write error when the AOF fsync policy is 'always'. Exiting...");
exit(1);
} else {
/* Recover from failed write leaving data into the buffer. However
* set an error to stop accepting writes as long as the error
* condition is not cleared. */
server.aof_last_write_status = REDIS_ERR;
/* Trim the sds buffer if there was a partial write, and there
* was no way to undo it with ftruncate(2). */
if (nwritten > 0) {
server.aof_current_size += nwritten;
sdsrange(server.aof_buf,nwritten,-1);
}
return; /* We'll try again on the next call... */
}
} else {
/* Successful write(2). If AOF was in error state, restore the
* OK state and log the event. */
if (server.aof_last_write_status == REDIS_ERR) {
redisLog(REDIS_WARNING,
"AOF write error looks solved, Redis can write again.");
server.aof_last_write_status = REDIS_OK;
}
}
server.aof_current_size += nwritten;
/* Re-use AOF buffer when it is small enough. The maximum comes from the
* arena size of 4k minus some overhead (but is otherwise arbitrary). */
if ((sdslen(server.aof_buf)+sdsavail(server.aof_buf)) < 4000) {
sdsclear(server.aof_buf);
} else {
sdsfree(server.aof_buf);
server.aof_buf = sdsempty();
}
/* Don't fsync if no-appendfsync-on-rewrite is set to yes and there are
* children doing I/O in the background. */
if (server.aof_no_fsync_on_rewrite &&
(server.aof_child_pid != -1 || server.rdb_child_pid != -1))
return;
/* Perform the fsync if needed. */
if (server.aof_fsync == AOF_FSYNC_ALWAYS) {
/* aof_fsync is defined as fdatasync() for Linux in order to avoid
* flushing metadata. */
aof_fsync(server.aof_fd); /* Let's try to get this data on the disk */
server.aof_last_fsync = server.unixtime;
} else if ((server.aof_fsync == AOF_FSYNC_EVERYSEC &&
server.unixtime > server.aof_last_fsync)) {
if (!sync_in_progress) aof_background_fsync(server.aof_fd);
server.aof_last_fsync = server.unixtime;
}
}
