/* 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.aof_rewrite_buf.
* 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.aof_rewrite_buf 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;
long long start;
if (server.aof_child_pid != -1) return REDIS_ERR;
start = ustime();
if ((childpid = fork()) == 0) {
char tmpfile[256];
/* Child */
closeListeningSockets(0);
redisSetProcTitle("redis-aof-rewrite");
snprintf(tmpfile,256,"temp-rewriteaof-bg-%d.aof", (int) getpid());
if (rewriteAppendOnlyFile(tmpfile) == REDIS_OK) {
size_t private_dirty = zmalloc_get_private_dirty();
if (private_dirty) {
redisLog(REDIS_NOTICE,
"AOF rewrite: %zu MB of memory used by copy-on-write",
private_dirty/(1024*1024));
}
exitFromChild(0);
} else {
exitFromChild(1);
}
} else {
/* Parent */
server.stat_fork_time = ustime()-start;
server.stat_fork_rate = (double) zmalloc_used_memory() * 1000000 / server.stat_fork_time / (1024*1024*1024); /* GB per second. */
latencyAddSampleIfNeeded("fork",server.stat_fork_time/1000);
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.aof_rewrite_scheduled = 0;
server.aof_rewrite_time_start = time(NULL);
server.aof_child_pid = 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.aof_rewrite_buf will start
* with a SELECT statement and it will be safe to merge. */
server.aof_selected_db = -1;
replicationScriptCacheFlush();
return REDIS_OK;
}
return REDIS_OK; /* unreached */
}
// This function is meant to be an exact replica of the fork() child path in rdbSaveToSlavesSockets
int do_socketSave2(int *fds, int numfds, uint64_t *clientids)
{
#ifndef NO_QFORKIMPL
int retval;
rio slave_sockets;
server.rdb_child_pid = GetCurrentProcessId();
rioInitWithFdset(&slave_sockets,fds,numfds);
zfree(fds);
// On Windows we haven't duplicated the listening sockets so we shouldn't close them
#ifndef _WIN32
closeListeningSockets(0);
#endif
redisSetProcTitle("redis-rdb-to-slaves");
retval = rdbSaveRioWithEOFMark(&slave_sockets,NULL);
if (retval == REDIS_OK && rioFlush(&slave_sockets) == 0)
retval = REDIS_ERR;
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));
}
/* If we are returning OK, at least one slave was served
* with the RDB file as expected, so we need to send a report
* to the parent via the pipe. The format of the message is:
*
* <len> <slave[0].id> <slave[0].error> ...
*
* len, slave IDs, and slave errors, are all uint64_t integers,
* so basically the reply is composed of 64 bits for the len field
* plus 2 additional 64 bit integers for each entry, for a total
* of 'len' entries.
*
* The 'id' represents the slave's client ID, so that the master
* can match the report with a specific slave, and 'error' is
* set to 0 if the replication process terminated with a success
* or the error code if an error occurred. */
void *msg = zmalloc(sizeof(uint64_t)*(1+2*numfds));
uint64_t *len = msg;
uint64_t *ids = len+1;
int j, msglen;
*len = numfds;
for (j = 0; j < numfds; j++) {
*ids++ = clientids[j];
*ids++ = slave_sockets.io.fdset.state[j];
}
/* Write the message to the parent. If we have no good slaves or
* we are unable to transfer the message to the parent, we exit
* with an error so that the parent will abort the replication
* process with all the childre that were waiting. */
msglen = sizeof(uint64_t)*(1+2*numfds);
if (*len == 0 ||
write(server.rdb_pipe_write_result_to_parent,msg,msglen)
!= msglen)
{
retval = REDIS_ERR;
}
}
return retval;
#endif
return REDIS_OK;
}