文章目录
- redis 的持久化机制
- RDB
- 定时生成RDB文件
- 后台生成RDB文件
- 生成RDB文件
- 将redis数据写入RDB文件中
- 对每个键值对的写入
redis 的持久化机制
redis有两种持久化机制，RDB && AOF，关于其概念在我的redis系列里都有，这里就不再赘述啦
RDB
RDB的执行有两种流程，一种是在配置文件中设置每n个键被修改就触发一次RDB快照，一种是通过bigsave命令。
定时生成RDB文件
RDB 通过 serverCron 函数实现定时生成 RDB 文件的任务，让我们来看一下：
代码语言：javascript复制/* This is our timer interrupt, called server.hz times per second.
* Here is where we do a number of things that need to be done asynchronously.
* For instance:
*
* - Active expired keys collection (it is also performed in a lazy way on
* lookup).
* - Software watchdog.
* - Update some statistic.
* - Incremental rehashing of the DBs hash tables.
* - Triggering BGSAVE / AOF rewrite, and handling of terminated children.
* - Clients timeout of different kinds.
* - Replication reconnection.
* - Many more...
*
* Everything directly called here will be called server.hz times per second,
* so in order to throttle execution of things we want to do less frequently
* a macro is used: run_with_period(milliseconds) { .... }
*/
int serverCron(struct aeEventLoop *eventLoop, long long id, void *clientData) {
int j;
UNUSED(eventLoop);
UNUSED(id);
UNUSED(clientData);
/* Software watchdog: deliver the SIGALRM that will reach the signal
* handler if we don't return here fast enough. */
if (server.watchdog_period) watchdogScheduleSignal(server.watchdog_period);
/* Update the time cache. */
updateCachedTime(1);
server.hz = server.config_hz;
/* Adapt the server.hz value to the number of configured clients. If we have
* many clients, we want to call serverCron() with an higher frequency. */
if (server.dynamic_hz) {
while (listLength(server.clients) / server.hz >
MAX_CLIENTS_PER_CLOCK_TICK)
{
server.hz *= 2;
if (server.hz > CONFIG_MAX_HZ) {
server.hz = CONFIG_MAX_HZ;
break;
}
}
}
run_with_period(100) {
trackInstantaneousMetric(STATS_METRIC_COMMAND,server.stat_numcommands);
trackInstantaneousMetric(STATS_METRIC_NET_INPUT,
server.stat_net_input_bytes);
trackInstantaneousMetric(STATS_METRIC_NET_OUTPUT,
server.stat_net_output_bytes);
}
/* We have just LRU_BITS bits per object for LRU information.
* So we use an (eventually wrapping) LRU clock.
*
* Note that even if the counter wraps it's not a big problem,
* everything will still work but some object will appear younger
* to Redis. However for this to happen a given object should never be
* touched for all the time needed to the counter to wrap, which is
* not likely.
*
* Note that you can change the resolution altering the
* LRU_CLOCK_RESOLUTION define. */
server.lruclock = getLRUClock();
/* Record the max memory used since the server was started. */
if (zmalloc_used_memory() > server.stat_peak_memory)
server.stat_peak_memory = zmalloc_used_memory();
run_with_period(100) {
/* Sample the RSS and other metrics here since this is a relatively slow call.
* We must sample the zmalloc_used at the same time we take the rss, otherwise
* the frag ratio calculate may be off (ratio of two samples at different times) */
server.cron_malloc_stats.process_rss = zmalloc_get_rss();
server.cron_malloc_stats.zmalloc_used = zmalloc_used_memory();
/* Sampling the allcator info can be slow too.
* The fragmentation ratio it'll show is potentically more accurate
* it excludes other RSS pages such as: shared libraries, LUA and other non-zmalloc
* allocations, and allocator reserved pages that can be pursed (all not actual frag) */
zmalloc_get_allocator_info(&server.cron_malloc_stats.allocator_allocated,
&server.cron_malloc_stats.allocator_active,
&server.cron_malloc_stats.allocator_resident);
/* in case the allocator isn't providing these stats, fake them so that
* fragmention info still shows some (inaccurate metrics) */
if (!server.cron_malloc_stats.allocator_resident) {
/* LUA memory isn't part of zmalloc_used, but it is part of the process RSS,
* so we must desuct it in order to be able to calculate correct
* "allocator fragmentation" ratio */
size_t lua_memory = lua_gc(server.lua,LUA_GCCOUNT,0)*1024LL;
server.cron_malloc_stats.allocator_resident = server.cron_malloc_stats.process_rss - lua_memory;
}
if (!server.cron_malloc_stats.allocator_active)
server.cron_malloc_stats.allocator_active = server.cron_malloc_stats.allocator_resident;
if (!server.cron_malloc_stats.allocator_allocated)
server.cron_malloc_stats.allocator_allocated = server.cron_malloc_stats.zmalloc_used;
}
/* We received a SIGTERM, shutting down here in a safe way, as it is
* not ok doing so inside the signal handler. */
if (server.shutdown_asap) {
if (prepareForShutdown(SHUTDOWN_NOFLAGS) == C_OK) exit(0);
serverLog(LL_WARNING,"SIGTERM received but errors trying to shut down the server, check the logs for more information");
server.shutdown_asap = 0;
}
/* Show some info about non-empty databases */
run_with_period(5000) {
for (j = 0; j < server.dbnum; j ) {
long long size, used, vkeys;
size = dictSlots(server.db[j].dict);
used = dictSize(server.db[j].dict);
vkeys = dictSize(server.db[j].expires);
if (used || vkeys) {
serverLog(LL_VERBOSE,"DB %d: %lld keys (%lld volatile) in %lld slots HT.",j,used,vkeys,size);
/* dictPrintStats(server.dict); */
}
}
}
/* Show information about connected clients */
if (!server.sentinel_mode) {
run_with_period(5000) {
serverLog(LL_DEBUG,
"%lu clients connected (%lu replicas), %zu bytes in use",
listLength(server.clients)-listLength(server.slaves),
listLength(server.slaves),
zmalloc_used_memory());
}
}
/* We need to do a few operations on clients asynchronously. */
clientsCron();
/* Handle background operations on Redis databases. */
databasesCron();
/* Start a scheduled AOF rewrite if this was requested by the user while
* a BGSAVE was in progress. */
if (!hasActiveChildProcess() &&
server.aof_rewrite_scheduled)
{
rewriteAppendOnlyFileBackground();
}
/* Check if a background saving or AOF rewrite in progress terminated. */
if (hasActiveChildProcess() || ldbPendingChildren())
{
checkChildrenDone();
} else {
/* If there is not a background saving/rewrite in progress check if
* we have to save/rewrite now. */
for (j = 0; j < server.saveparamslen; j ) {
struct saveparam *sp = server.saveparams j;
/* Save if we reached the given amount of changes,
* the given amount of seconds, and if the latest bgsave was
* successful or if, in case of an error, at least
* CONFIG_BGSAVE_RETRY_DELAY seconds already elapsed. */
if (server.dirty >= sp->changes &&
server.unixtime-server.lastsave > sp->seconds &&
(server.unixtime-server.lastbgsave_try >
CONFIG_BGSAVE_RETRY_DELAY ||
server.lastbgsave_status == C_OK))
{
serverLog(LL_NOTICE,"%d changes in %d seconds. Saving...",
sp->changes, (int)sp->seconds);
rdbSaveInfo rsi, *rsiptr;
rsiptr = rdbPopulateSaveInfo(&rsi);
rdbSaveBackground(server.rdb_filename,rsiptr);
break;
}
}
/* Trigger an AOF rewrite if needed. */
if (server.aof_state == AOF_ON &&
!hasActiveChildProcess() &&
server.aof_rewrite_perc &&
server.aof_current_size > server.aof_rewrite_min_size)
{
long long base = server.aof_rewrite_base_size ?
server.aof_rewrite_base_size : 1;
long long growth = (server.aof_current_size*100/base) - 100;
if (growth >= server.aof_rewrite_perc) {
serverLog(LL_NOTICE,"Starting automatic rewriting of AOF on %lld%% growth",growth);
rewriteAppendOnlyFileBackground();
}
}
}
/* AOF postponed flush: Try at every cron cycle if the slow fsync
* completed. */
if (server.aof_flush_postponed_start) flushAppendOnlyFile(0);
/* AOF write errors: in this case we have a buffer to flush as well and
* clear the AOF error in case of success to make the DB writable again,
* however to try every second is enough in case of 'hz' is set to
* an higher frequency. */
run_with_period(1000) {
if (server.aof_last_write_status == C_ERR)
flushAppendOnlyFile(0);
}
/* Clear the paused clients flag if needed. */
clientsArePaused(); /* Don't check return value, just use the side effect.*/
/* Replication cron function -- used to reconnect to master,
* detect transfer failures, start background RDB transfers and so forth. */
run_with_period(1000) replicationCron();
/* Run the Redis Cluster cron. */
run_with_period(100) {
if (server.cluster_enabled) clusterCron();
}
/* Run the Sentinel timer if we are in sentinel mode. */
if (server.sentinel_mode) sentinelTimer();
/* Cleanup expired MIGRATE cached sockets. */
run_with_period(1000) {
migrateCloseTimedoutSockets();
}
/* Stop the I/O threads if we don't have enough pending work. */
stopThreadedIOIfNeeded();
/* Resize tracking keys table if needed. This is also done at every
* command execution, but we want to be sure that if the last command
* executed changes the value via CONFIG SET, the server will perform
* the operation even if completely idle. */
if (server.tracking_clients) trackingLimitUsedSlots();
/* Start a scheduled BGSAVE if the corresponding flag is set. This is
* useful when we are forced to postpone a BGSAVE because an AOF
* rewrite is in progress.
*
* Note: this code must be after the replicationCron() call above so
* make sure when refactoring this file to keep this order. This is useful
* because we want to give priority to RDB savings for replication. */
if (!hasActiveChildProcess() &&
server.rdb_bgsave_scheduled &&
(server.unixtime-server.lastbgsave_try > CONFIG_BGSAVE_RETRY_DELAY ||
server.lastbgsave_status == C_OK))
{
rdbSaveInfo rsi, *rsiptr;
rsiptr = rdbPopulateSaveInfo(&rsi);
if (rdbSaveBackground(server.rdb_filename,rsiptr) == C_OK)
server.rdb_bgsave_scheduled = 0;
}
/* Fire the cron loop modules event. */
RedisModuleCronLoopV1 ei = {REDISMODULE_CRON_LOOP_VERSION,server.hz};
moduleFireServerEvent(REDISMODULE_EVENT_CRON_LOOP,
0,
&ei);
server.cronloops ;
return 1000/server.hz;
}后台生成RDB文件
rdb 通过 rdbSaveBackground 函数负责在后台生成 RDB 文件（bigsave的底层也是这个），创建一个子进程（前面那个函数最终也会调用到这里），由子进程将数据快照保存到磁盘中，父进程继续该干嘛干嘛。
代码语言：javascript复制int rdbSaveBackground(char *filename, rdbSaveInfo *rsi) {
pid_t childpid;
if (hasActiveChildProcess()) return C_ERR;
server.dirty_before_bgsave = server.dirty;
server.lastbgsave_try = time(NULL);
openChildInfoPipe();
if ((childpid = redisFork()) == 0) {
int retval;
/* Child */
redisSetProcTitle("redis-rdb-bgsave");
redisSetCpuAffinity(server.bgsave_cpulist);
retval = rdbSave(filename,rsi);
if (retval == C_OK) {
sendChildCOWInfo(CHILD_INFO_TYPE_RDB, "RDB");
}
exitFromChild((retval == C_OK) ? 0 : 1);
} else {
/* Parent */
if (childpid == -1) {
closeChildInfoPipe();
server.lastbgsave_status = C_ERR;
serverLog(LL_WARNING,"Can't save in background: fork: %s",
strerror(errno));
return C_ERR;
}
serverLog(LL_NOTICE,"Background saving started by pid %d",childpid);
server.rdb_save_time_start = time(NULL);
server.rdb_child_pid = childpid;
server.rdb_child_type = RDB_CHILD_TYPE_DISK;
return C_OK;
}
return C_OK; /* unreached */
}生成RDB文件
上面的函数最终会执行如下代码（这个代码属于save命令，后面再说关于这个命令）：
代码语言：javascript复制/* Save the DB on disk. Return C_ERR on error, C_OK on success. */
int rdbSave(char *filename, rdbSaveInfo *rsi) {
char tmpfile[256];
char cwd[MAXPATHLEN]; /* Current working dir path for error messages. */
FILE *fp;
rio rdb;
int error = 0;
snprintf(tmpfile,256,"temp-%d.rdb", (int) getpid());
fp = fopen(tmpfile,"w");
if (!fp) {
char *cwdp = getcwd(cwd,MAXPATHLEN);
serverLog(LL_WARNING,
"Failed opening the RDB file %s (in server root dir %s) "
"for saving: %s",
filename,
cwdp ? cwdp : "unknown",
strerror(errno));
return C_ERR;
}
rioInitWithFile(&rdb,fp);
startSaving(RDBFLAGS_NONE);
if (server.rdb_save_incremental_fsync)
rioSetAutoSync(&rdb,REDIS_AUTOSYNC_BYTES);
if (rdbSaveRio(&rdb,&error,RDBFLAGS_NONE,rsi) == C_ERR) {
errno = error;
goto werr;
}
/* Make sure data will not remain on the OS's output buffers */
if (fflush(fp) == EOF) goto werr;
if (fsync(fileno(fp)) == -1) goto werr;
if (fclose(fp) == EOF) goto werr;
/* Use RENAME to make sure the DB file is changed atomically only
* if the generate DB file is ok. */
if (rename(tmpfile,filename) == -1) {
char *cwdp = getcwd(cwd,MAXPATHLEN);
serverLog(LL_WARNING,
"Error moving temp DB file %s on the final "
"destination %s (in server root dir %s): %s",
tmpfile,
filename,
cwdp ? cwdp : "unknown",
strerror(errno));
unlink(tmpfile);
stopSaving(0);
return C_ERR;
}
serverLog(LL_NOTICE,"DB saved on disk");
server.dirty = 0;
server.lastsave = time(NULL);
server.lastbgsave_status = C_OK;
stopSaving(1);
return C_OK;
werr:
serverLog(LL_WARNING,"Write error saving DB on disk: %s", strerror(errno));
fclose(fp);
unlink(tmpfile);
stopSaving(0);
return C_ERR;
}如果在生产环节中直接使用save，会导致主进程长时间阻塞，所以不应在生产环节中使用该命令。
将redis数据写入RDB文件中
上面那个函数最终乎调用到这个函数（真实一环扣一环呀）：
代码语言：javascript复制/* Produces a dump of the database in RDB format sending it to the specified
* Redis I/O channel. On success C_OK is returned, otherwise C_ERR
* is returned and part of the output, or all the output, can be
* missing because of I/O errors.
*
* When the function returns C_ERR and if 'error' is not NULL, the
* integer pointed by 'error' is set to the value of errno just after the I/O
* error. */
int rdbSaveRio(rio *rdb, int *error, int rdbflags, rdbSaveInfo *rsi) {
dictIterator *di = NULL;
dictEntry *de;
char magic[10];
int j;
uint64_t cksum;
size_t processed = 0;
if (server.rdb_checksum)
rdb->update_cksum = rioGenericUpdateChecksum;
snprintf(magic,sizeof(magic),"REDISd",RDB_VERSION);
if (rdbWriteRaw(rdb,magic,9) == -1) goto werr;
if (rdbSaveInfoAuxFields(rdb,rdbflags,rsi) == -1) goto werr;
if (rdbSaveModulesAux(rdb, REDISMODULE_AUX_BEFORE_RDB) == -1) goto werr;
for (j = 0; j < server.dbnum; j ) {
redisDb *db = server.db j;
dict *d = db->dict;
if (dictSize(d) == 0) continue;
di = dictGetSafeIterator(d);
/* Write the SELECT DB opcode */
if (rdbSaveType(rdb,RDB_OPCODE_SELECTDB) == -1) goto werr;
if (rdbSaveLen(rdb,j) == -1) goto werr;
/* Write the RESIZE DB opcode. */
uint64_t db_size, expires_size;
db_size = dictSize(db->dict);
expires_size = dictSize(db->expires);
if (rdbSaveType(rdb,RDB_OPCODE_RESIZEDB) == -1) goto werr;
if (rdbSaveLen(rdb,db_size) == -1) goto werr;
if (rdbSaveLen(rdb,expires_size) == -1) goto werr;
/* Iterate this DB writing every entry */
while((de = dictNext(di)) != NULL) {
sds keystr = dictGetKey(de);
robj key, *o = dictGetVal(de);
long long expire;
initStaticStringObject(key,keystr);
expire = getExpire(db,&key);
if (rdbSaveKeyValuePair(rdb,&key,o,expire) == -1) goto werr;
/* When this RDB is produced as part of an AOF rewrite, move
* accumulated diff from parent to child while rewriting in
* order to have a smaller final write. */
if (rdbflags & RDBFLAGS_AOF_PREAMBLE &&
rdb->processed_bytes > processed AOF_READ_DIFF_INTERVAL_BYTES)
{
processed = rdb->processed_bytes;
aofReadDiffFromParent();
}
}
dictReleaseIterator(di);
di = NULL; /* So that we don't release it again on error. */
}
/* If we are storing the replication information on disk, persist
* the script cache as well: on successful PSYNC after a restart, we need
* to be able to process any EVALSHA inside the replication backlog the
* master will send us. */
if (rsi && dictSize(server.lua_scripts)) {
di = dictGetIterator(server.lua_scripts);
while((de = dictNext(di)) != NULL) {
robj *body = dictGetVal(de);
if (rdbSaveAuxField(rdb,"lua",3,body->ptr,sdslen(body->ptr)) == -1)
goto werr;
}
dictReleaseIterator(di);
di = NULL; /* So that we don't release it again on error. */
}
if (rdbSaveModulesAux(rdb, REDISMODULE_AUX_AFTER_RDB) == -1) goto werr;
/* EOF opcode */
if (rdbSaveType(rdb,RDB_OPCODE_EOF) == -1) goto werr;
/* CRC64 checksum. It will be zero if checksum computation is disabled, the
* loading code skips the check in this case. */
cksum = rdb->cksum;
memrev64ifbe(&cksum);
if (rioWrite(rdb,&cksum,8) == 0) goto werr;
return C_OK;
werr:
if (error) *error = errno;
if (di) dictReleaseIterator(di);
return C_ERR;
}对每个键值对的写入
好家伙，又继续下放。在上面的函数中，最终会调用到 rdbSaveKeyValuePair 函数，将每一个键值对写入到RDB文件中：
代码语言：javascript复制/* Save a key-value pair, with expire time, type, key, value.
* On error -1 is returned.
* On success if the key was actually saved 1 is returned, otherwise 0
* is returned (the key was already expired). */
int rdbSaveKeyValuePair(rio *rdb, robj *key, robj *val, long long expiretime) {
int savelru = server.maxmemory_policy & MAXMEMORY_FLAG_LRU;
int savelfu = server.maxmemory_policy & MAXMEMORY_FLAG_LFU;
/* Save the expire time */
if (expiretime != -1) {
if (rdbSaveType(rdb,RDB_OPCODE_EXPIRETIME_MS) == -1) return -1;
if (rdbSaveMillisecondTime(rdb,expiretime) == -1) return -1;
}
/* Save the LRU info. */
if (savelru) {
uint64_t idletime = estimateObjectIdleTime(val);
idletime /= 1000; /* Using seconds is enough and requires less space.*/
if (rdbSaveType(rdb,RDB_OPCODE_IDLE) == -1) return -1;
if (rdbSaveLen(rdb,idletime) == -1) return -1;
}
/* Save the LFU info. */
if (savelfu) {
uint8_t buf[1];
buf[0] = LFUDecrAndReturn(val);
/* We can encode this in exactly two bytes: the opcode and an 8
* bit counter, since the frequency is logarithmic with a 0-255 range.
* Note that we do not store the halving time because to reset it
* a single time when loading does not affect the frequency much. */
if (rdbSaveType(rdb,RDB_OPCODE_FREQ) == -1) return -1;
if (rdbWriteRaw(rdb,buf,1) == -1) return -1;
}
/* Save type, key, value */
if (rdbSaveObjectType(rdb,val) == -1) return -1;
if (rdbSaveStringObject(rdb,key) == -1) return -1;
if (rdbSaveObject(rdb,val,key) == -1) return -1;
/* Delay return if required (for testing) */
if (server.rdb_key_save_delay)
usleep(server.rdb_key_save_delay);
return 1;
}1、如果设置了过期时间，则写入 RDB_OPCODE_EXPIRETIME 标志和时间戳。 2、如果redis内存淘汰策略使用的是LRU算法和LFU算法，则记录键的空闲时间和LFU计数。 3、写入RDB键值对标志，再写入键内容
加载部分就不写了吧。。。
