When we upload many imgs to zimg server , and Why zimg Server return "Interner error " some times. about zimg HOT 3 OPEN

2015/01/24 02:51:51:389148 [DEBUG] ============post_request_cb() DONE!===============
2015/01/24 02:51:52:289019 [DEBUG] Method: 2
2015/01/24 02:51:52:289188 [DEBUG] evblen = 4365752
2015/01/24 02:51:52:294174 [DEBUG] rmblen = 4365752
2015/01/24 02:51:52:294251 [DEBUG] Begin to Save Image...
2015/01/24 02:51:52:294297 [DEBUG] Begin to Caculate MD5...
2015/01/24 02:51:52:315560 [DEBUG] md5: bc28b588de9b62973beeeeb36c2764ff
2015/01/24 02:51:52:321705 [DEBUG] key: bc28b588de9b62973beeeeb36c2764ff is not exist!
2015/01/24 02:51:52:321813 [DEBUG] exist_db not found. Begin to Save File.
2015/01/24 02:51:52:770086 [DEBUG] Failed to execute save [bc28b588de9b62973beeeeb36c2764ff] to ssdb.
2015/01/24 02:51:52:770220 [DEBUG] save_img_db failed.
2015/01/24 02:51:52:770269 [DEBUG] Image Save Failed!
2015/01/24 02:51:52:770311 [ERROR] 192.168.1.17 fail post save
2015/01/24 02:51:52:770356 [DEBUG] post_error_list[0]: Internal error.
2015/01/24 02:51:52:770475 [DEBUG] ret_str_unformat: {"ret":false,"error":{"code":0,"message":"Internal error."}}
2015/01/24 02:51:52:770565 [DEBUG] ============post_request_cb() ERROR!===============
2015/01/24 02:51:53:875783 [DEBUG] Method: 2
2015/01/24 02:51:53:875918 [DEBUG] evblen = 4234265
2015/01/24 02:51:53:880753 [DEBUG] rmblen = 4234265
2015/01/24 02:51:53:880828 [DEBUG] Begin to Save Image...
2015/01/24 02:51:53:880873 [DEBUG] Begin to Caculate MD5...
2015/01/24 02:51:53:901451 [DEBUG] md5: 4221cc63b2add09eb27ff420013e2553
2015/01/24 02:51:53:921534 [DEBUG] key: 4221cc63b2add09eb27ff420013e2553 is not exist!
2015/01/24 02:51:53:921644 [DEBUG] exist_db not found. Begin to Save File.
2015/01/24 02:51:54:051808 [DEBUG] Succeed to save [4221cc63b2add09eb27ff420013e2553] to ssdb. length = [4234265].
2015/01/24 02:51:54:051926 [DEBUG] save_img_db succ.
2015/01/24 02:51:54:051976 [INFO] 192.168.1.17 succ post pic:4221cc63b2add09eb27ff420013e2553 size:4234265
2015/01/24 02:51:54:052039 [DEBUG] ret_str_unformat: {"ret":true,"info":{"md5":"4221cc63b2add09eb27ff420013e2553","size":4234265}}
2015/01/24 02:51:54:052116 [DEBUG] ============post_request_cb() DONE!=============== 

LOG_PRINT(LOG_DEBUG, "Failed to execute save [%s] to ssdb: %s", cache_key, r->str);