Is conventional wisdom about the mechanism of red-eye reduction flawed?

As an example for a typical explanation about red-eye reduction pre-flashes, the description in the Metz SCA3202-M7 flash adapter manual states

Red eyes are always the result of a physical effect. This arises whenever a person looks more or less straight into the camera, the ambient light is relatively dark and the flash unit is mounted on or directly next to the camera. The flash unit illuminates the back of the eyes, revealing the blood filled retina through the pupil. This is recorded by the camera as a red spot in the eyes.

The red-eye reduction function brings about a significant improvement in this respect. When this facility is used the flash unit triggers, prior to shutter operation, a few weakly visible preflashes which are followed by the main flash. These preflashes induce the pupils to close down, thereby diminishing the red-eye effect.”

So here are three flash photographs of my eye taken with one self-timer, distance probably 8m. Focus to approx half the camera distance

Focus on camera

Focus quite near

There is no significant difference in iris size: if any, there is a small overall reduction throughout the (chronologically sorted) sequence with photographs taken with a distance of about 1sec.

Nevertheless the last image not even looking in the direction of the camera (with the reflexes from the flash being almost or entirely off the pupil) clearly has the strongest red-eye, followed by the first image.

The middle image, in spite of having the flash reflex basically straight in the pupil, clearly has a minimal amount of red-eye.

What gives? The typical description of the red-eye effect strangely does not take into account that the eye is an optical system designed to create a sharp image of what you are looking at on the retina. If there is no overlap of the image of the flash on the retina and the image of the camera’s entrance pupil (the aperture as viewed through the front lens), no retina area lit by the flash will be visible from the camera’s entrance pupil and consequently the sensor.

So the main objective of a pre-flash to me appears to be making the eye focus on flash and camera so that their respective images on the retina are sharp and disparate. While reducing the iris size would also help by increasing the eye’s depth of focus (and thus decreasing blurring of the retina images), the effect seems minor compared to what the focus reflex can achieve here even with comparatively wide pupil.

So contrary to conventional wisdom, staring straight and focusedly at camera/flash (or a birdie waved at same distance) will do most of the work even without preflash. An urgently blinking self-timer lamp should be almost equally effective for red-eye prevention as a pre-flash.

Now the people writing about cameras and designing red-eye reduction systems know their place inside out optics. It seems preposterous to assume that they of all people would not consider the implications of the eye being an imaging device after which cameras have been modeled complete with lens, aperture, and sensor surface. And money is riding on it: basically every camera review tests for red-eye.

What am I overlooking?

New ecommerce site for wearables, question about products names

Hi guys,
I'm setting my e-commerce site for wearables.

I have different products, that are kind of similar
so, for example, watches for kids

I will start with 3 models, that are kind of similar on functionality, but different look.

Now how do I name them?

By the reference the Chinese manufacturer gives them?… XCYY-34

Or should I come with a name for the product?… CoolWatch misty


MySQL crashing at about 70k open files

Server running community 8.0.14, we hit the number of open files a few days ago, so I increased the limit but after a while the server crashed with this in the error log:

InnoDB: We intentionally generate a memory trap. InnoDB: Submit a detailed bug report to InnoDB: If you get repeated assertion failures or crashes, even InnoDB: immediately after the mysqld startup, there may be InnoDB: corruption in the InnoDB tablespace. Please refer to InnoDB: InnoDB: about forcing recovery. 03:07:21 UTC - mysqld got signal 6 ; This could be because you hit a bug. It is also possible that this binary or one of the libraries it was linked against is corrupt, improperly built, or misconfigured. This error can also be caused by malfunctioning hardware. Attempting to collect some information that could help diagnose the problem. As this is a crash and something is definitely wrong, the information collection process might fail.  key_buffer_size=8388608 read_buffer_size=131072 max_used_connections=221 max_threads=1000 thread_count=4 connection_count=3 It is possible that mysqld could use up to key_buffer_size + (read_buffer_size + sort_buffer_size)*max_threads = 403301 K  bytes of memory Hope that's ok; if not, decrease some variables in the equation.  Thread pointer: 0x7f9200000b20 Attempting backtrace. You can use the following information to find out where mysqld died. If you see no messages after this, something went terribly wrong... stack_bottom = 7fd571ceaca0 thread_stack 0x46000 /usr/sbin/mysqld(my_print_stacktrace(unsigned char*, unsigned long)+0x3d) [0x561bdb69757d] /usr/sbin/mysqld(handle_fatal_signal+0x423) [0x561bda8277c3] /lib/x86_64-linux-gnu/ [0x7fe5095f6890] /lib/x86_64-linux-gnu/ [0x7fe507981e97] /lib/x86_64-linux-gnu/ [0x7fe507983801] /usr/sbin/mysqld(ut_dbg_assertion_failed(char const*, char const*, unsigned long)+0x2d5) [0x561bdb94d2c5] /usr/sbin/mysqld(+0x1fe243c) [0x561bdb94f43c] /usr/sbin/mysqld(mem_heap_create_block_func(mem_block_info_t*, unsigned long, unsigned long)+0x9ba) [0x561bdb95638a] /usr/sbin/mysqld(mem_heap_add_block(mem_block_info_t*, unsigned long)+0x72) [0x561bdb956562] /usr/sbin/mysqld(trx_undo_update_rec_get_update(unsigned char const*, dict_index_t*, unsigned long, unsigned long, unsigned long, unsigned long, trx_t*, mem_block_info_t*, upd_t**, lob::undo_vers_t*, type_cmpl_t&)+0x1926) [0x561bdb924896] /usr/sbin/mysqld(row_purge_step(que_thr_t*)+0x845) [0x561bdb8b7ad5] /usr/sbin/mysqld(que_run_threads(que_thr_t*)+0x997) [0x561bdb859597] /usr/sbin/mysqld(srv_worker_thread()+0x29d) [0x561bdb8e85bd] /usr/sbin/mysqld(std::thread::_State_impl<std::thread::_Invoker<std::tuple<Runnable, void (*)()> > >::_M_run()+0x63) [0x561bdb759883] /usr/lib/x86_64-linux-gnu/ [0x7fe5083a757f] /lib/x86_64-linux-gnu/ [0x7fe5095eb6db] /lib/x86_64-linux-gnu/ [0x7fe507a6488f]  Trying to get some variables. Some pointers may be invalid and cause the dump to abort. Query (0): Connection ID (thread ID): 0 Status: NOT_KILLED  The manual page at contains information that should help you find out what is causing the crash. 2019-01-27T03:07:37.554520Z 0 [System] [MY-010116] [Server] /usr/sbin/mysqld (mysqld 8.0.14) starting as process 56489  InnoDB: Progress in percents: 1InnoDB MEMCACHED: Memcached uses atomic increment  2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 1002019-01-27T03:12:07.973920Z 0 [System] [MY-010229] [Server] Starting crash recovery... 2019-01-27T03:12:07.982255Z 0 [System] [MY-010232] [Server] Crash recovery finished. 2019-01-27T03:12:10.581437Z 0 [Warning] [MY-010068] [Server] CA certificate ca.pem is self signed. 2 

The machine is a 2x Xeon E5-2680v4 – 28c/56t – 2.4GHz /3.3GHz with 512GB RAM, configuration file:

server-id = 1 log-bin   = /var/lib/mysql-binlogs/web07 relay-log = web07-relay-bin  binlog_expire_logs_seconds = 259200  open_files_limit = 10000 max_connections = 1000  innodb_flush_method=O_DIRECT innodb_flush_log_at_trx_commit=0 innodb_log_file_size=38G  innodb_buffer_pool_size=300G innodb_buffer_pool_instances=64  join_buffer_size=5M tmp_table_size=1G max_heap_table_size=512M skip_name_resolve=1  table_open_cache=20000  sql-mode="ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION,NO_AUTO_VALUE_ON_ZERO"  relay-log-recovery=1  default-authentication-plugin=mysql_native_password 

After that crash, the server crashes again if I don’t restart it when the open files become too many (every about 24 hours), this is now for example:

$   mysql -e "show global status like 'open_%';" +--------------------------+-------+ | Variable_name            | Value | +--------------------------+-------+ | Open_files               | 62507 | | Open_streams             | 0     | | Open_table_definitions   | 1843  | | Open_tables              | 18779 | | Opened_files             | 71902 | | Opened_table_definitions | 3168  | | Opened_tables            | 18803 | +--------------------------+-------+ 

While I was writing this question, the server crashed:

2019-01-29T22:27:51.031406Z 54298197 [ERROR] [MY-013132] [Server] The table '/tmp/#sql9ae8_33c8655_13' is full!

2019-01-29T22:28:01.844610Z 54321796 [ERROR] [MY-013132] [Server] The table '/tmp/#sql9ae8_33ce284_1' is full!

How can I debug why there are so many open files? The traffic is high but usually there are no more than 10 connections open, so why the temporary tables are not closed?

enter image description here