前些天一台redis机器硬盘写满了,主要是由于程序bug导致备份量激增,而恰好监控程序的通知机制也罢工了,于是第一次体验到了redis的罢工(只读不写)。 现在我们来看下在磁盘写满后redis的处理机制: save流程:serverCron-rdbSaveBackground-rdbSave save后
前些天一台redis机器硬盘写满了,主要是由于程序bug导致备份量激增,而恰好监控程序的通知机制也罢工了,于是第一次体验到了redis的罢工(只读不写)。
现在我们来看下在磁盘写满后redis的处理机制:受其影响,processCommand和luaRedisGenericCommand中判断如果是写操作,则直接返回REDIS_OK,而没有实际写入
1.rdbSave所有的写出错都会返回REDIS_ERR
int rdbSave(char *filename) { dictIterator *di = NULL; dictEntry *de; char tmpfile[256]; char magic[10]; int j; long long now = mstime(); FILE *fp; rio rdb; uint64_t cksum; snprintf(tmpfile,256,"temp-%d.rdb", (int) getpid()); fp = fopen(tmpfile,"w"); if (!fp) { redisLog(REDIS_WARNING, "Failed opening .rdb for saving: %s", strerror(errno)); return REDIS_ERR; } rioInitWithFile(&rdb,fp); if (server.rdb_checksum) rdb.update_cksum = rioGenericUpdateChecksum; snprintf(magic,sizeof(magic),"REDIS%04d",REDIS_RDB_VERSION); if (rdbWriteRaw(&rdb,magic,9) == -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); if (!di) { fclose(fp); return REDIS_ERR; } /* Write the SELECT DB opcode */ if (rdbSaveType(&rdb,REDIS_RDB_OPCODE_SELECTDB) == -1) goto werr; if (rdbSaveLen(&rdb,j) == -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,now) == -1) goto werr; } dictReleaseIterator(di); } di = NULL; /* So that we don't release it again on error. */ /* EOF opcode */ if (rdbSaveType(&rdb,REDIS_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; /* 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) { redisLog(REDIS_WARNING,"Error moving temp DB file on the final destination: %s", strerror(errno)); unlink(tmpfile); return REDIS_ERR; } redisLog(REDIS_NOTICE,"DB saved on disk"); server.dirty = 0; server.lastsave = time(NULL); server.lastbgsave_status = REDIS_OK; return REDIS_OK; werr: fclose(fp); unlink(tmpfile); redisLog(REDIS_WARNING,"Write error saving DB on disk: %s", strerror(errno)); if (di) dictReleaseIterator(di); return REDIS_ERR; }
2.rdbSaveBackground中,如果子进程调用rdbsave返回REDIS_ERR,那么子进程exit(1)
int rdbSaveBackground(char *filename) { pid_t childpid; long long start; if (server.rdb_child_pid != -1) return REDIS_ERR; server.dirty_before_bgsave = server.dirty; server.lastbgsave_try = time(NULL); start = ustime(); if ((childpid = fork()) == 0) { int retval; /* Child */ closeListeningSockets(0); redisSetProcTitle("redis-rdb-bgsave"); retval = rdbSave(filename); if (retval == REDIS_OK) { size_t private_dirty = zmalloc_get_private_dirty(); if (private_dirty) { redisLog(REDIS_NOTICE, "RDB: %zu MB of memory used by copy-on-write", private_dirty/(1024*1024)); } } exitFromChild((retval == REDIS_OK) ? 0 : 1); //进程退出时返回0/1 } else { /* Parent */ server.stat_fork_time = ustime()-start; if (childpid == -1) { server.lastbgsave_status = REDIS_ERR; redisLog(REDIS_WARNING,"Can't save in background: fork: %s", strerror(errno)); return REDIS_ERR; } redisLog(REDIS_NOTICE,"Background saving started by pid %d",childpid); server.rdb_save_time_start = time(NULL); server.rdb_child_pid = childpid; updateDictResizePolicy(); return REDIS_OK; } return REDIS_OK; /* unreached */ }
/* Check if a background saving or AOF rewrite in progress terminated. */ if (server.rdb_child_pid != -1 || server.aof_child_pid != -1) { int statloc; pid_t pid; if ((pid = wait3(&statloc,WNOHANG,NULL)) != 0) { int exitcode = WEXITSTATUS(statloc); int bysignal = 0; if (WIFSIGNALED(statloc)) bysignal = WTERMSIG(statloc); if (pid == server.rdb_child_pid) { backgroundSaveDoneHandler(exitcode,bysignal); //根据bgsave子进程的exitcode以及是否由信号结束的标签进行后续处理 } else if (pid == server.aof_child_pid) { backgroundRewriteDoneHandler(exitcode,bysignal); } else { redisLog(REDIS_WARNING, "Warning, detected child with unmatched pid: %ld", (long)pid); } updateDictResizePolicy(); } }
void backgroundSaveDoneHandler(int exitcode, int bysignal) { if (!bysignal && exitcode == 0) { redisLog(REDIS_NOTICE, "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; //状态转换 } else { mstime_t latency; redisLog(REDIS_WARNING, "Background saving terminated by signal %d", bysignal); latencyStartMonitor(latency); rdbRemoveTempFile(server.rdb_child_pid); latencyEndMonitor(latency); latencyAddSampleIfNeeded("rdb-unlink-temp-file",latency); /* SIGUSR1 is whitelisted, so we have a way to kill a child without * tirggering an error conditon. */ if (bysignal != SIGUSR1) server.lastbgsave_status = REDIS_ERR; } server.rdb_child_pid = -1; server.rdb_save_time_last = time(NULL)-server.rdb_save_time_start; server.rdb_save_time_start = -1; /* Possibly there are slaves waiting for a BGSAVE in order to be served * (the first stage of SYNC is a bulk transfer of dump.rdb) */ updateSlavesWaitingBgsave((!bysignal && exitcode == 0) ? REDIS_OK : REDIS_ERR); }
/* Don't accept write commands if there are problems persisting on disk * and if this is a master instance. */ if (((server.stop_writes_on_bgsave_err && server.saveparamslen > 0 && server.lastbgsave_status == REDIS_ERR) || server.aof_last_write_status == REDIS_ERR) && server.masterhost == NULL && (c->cmd->flags & REDIS_CMD_WRITE || c->cmd->proc == pingCommand)) { flagTransaction(c); if (server.aof_last_write_status == REDIS_OK) addReply(c, shared.bgsaveerr); else addReplySds(c, sdscatprintf(sdsempty(), "-MISCONF Errors writing to the AOF file: %s\r\n", strerror(server.aof_last_write_errno))); return REDIS_OK; }
/* Write commands are forbidden against read-only slaves, or if a * command marked as non-deterministic was already called in the context * of this script. */ if (cmd->flags & REDIS_CMD_WRITE) { if (server.lua_random_dirty) { luaPushError(lua, "Write commands not allowed after non deterministic commands"); goto cleanup; } else if (server.masterhost && server.repl_slave_ro && !server.loading && !(server.lua_caller->flags & REDIS_MASTER)) { luaPushError(lua, shared.roslaveerr->ptr); goto cleanup; } else if (server.stop_writes_on_bgsave_err && server.saveparamslen > 0 && server.lastbgsave_status == REDIS_ERR) { luaPushError(lua, shared.bgsaveerr->ptr); goto cleanup; } } cleanup: /* Clean up. Command code may have changed argv/argc so we use the * argv/argc of the client instead of the local variables. */ for (j = 0; j < c->argc; j++) { robj *o = c->argv[j]; /* Try to cache the object in the cached_objects array. * The object must be small, SDS-encoded, and with refcount = 1 * (we must be the only owner) for us to cache it. */ if (j < LUA_CMD_OBJCACHE_SIZE && o->refcount == 1 && o->encoding == REDIS_ENCODING_RAW && sdslen(o->ptr) <= LUA_CMD_OBJCACHE_MAX_LEN) { struct sdshdr *sh = (void*)(((char*)(o->ptr))-(sizeof(struct sdshdr))); if (cached_objects[j]) decrRefCount(cached_objects[j]); cached_objects[j] = o; cached_objects_len[j] = sh->free + sh->len; } else { decrRefCount(o); } } if (c->argv != argv) { zfree(c->argv); argv = NULL; } if (raise_error) { /* If we are here we should have an error in the stack, in the * form of a table with an "err" field. Extract the string to * return the plain error. */ lua_pushstring(lua,"err"); lua_gettable(lua,-2); return lua_error(lua); } return 1;