MySQL: many Sleep processes I've queried SHOW processlist as root after a server restert, and got a long list of Sleep threads:

+-----+-------------+-----------------+---------+---------+------+-------+------------------+
| Id  | User        | Host            | db      | Command | Time | State | Info             |
+-----+-------------+-----------------+---------+---------+------+-------+------------------+
| 217 | root        | localhost       | masters | Sleep   |  371 |       | NULL             |
| 251 | mastersuser | localhost:50883 | masters | Sleep   |  297 |       | NULL             |
| 252 | mastersuser | localhost:50884 | masters | Sleep   |  297 |       | NULL             |
| 253 | mastersuser | localhost:50885 | masters | Sleep   |  297 |       | NULL             |
| 254 | mastersuser | localhost:50891 | masters | Sleep   |  296 |       | NULL             |
| 261 | mastersuser | localhost:50897 | masters | Sleep   |  281 |       | NULL             |
| 260 | mastersuser | localhost:50896 | masters | Sleep   |  281 |       | NULL             |
| 262 | mastersuser | localhost:50899 | masters | Sleep   |  281 |       | NULL             |
| 263 | mastersuser | localhost:50900 | masters | Sleep   |  280 |       | NULL             |
| 272 | mastersuser | localhost:50908 | masters | Sleep   |  263 |       | NULL             |
| 273 | mastersuser | localhost:50909 | masters | Sleep   |  263 |       | NULL             |
| 274 | mastersuser | localhost:50911 | masters | Sleep   |  263 |       | NULL             |
| 275 | mastersuser | localhost:50912 | masters | Sleep   |  263 |       | NULL             |
| 287 | mastersuser | localhost:52434 | masters | Sleep   |  242 |       | NULL             |
| 288 | mastersuser | localhost:52435 | masters | Sleep   |  242 |       | NULL             |
| 289 | mastersuser | localhost:52436 | masters | Sleep   |  242 |       | NULL             |
| 290 | mastersuser | localhost:52437 | masters | Sleep   |  242 |       | NULL             |
| 296 | mastersuser | localhost:52445 | masters | Sleep   |  233 |       | NULL             |
| 298 | mastersuser | localhost:52446 | masters | Sleep   |  232 |       | NULL             |
| 299 | mastersuser | localhost:52447 | masters | Sleep   |  232 |       | NULL             |
| 300 | mastersuser | localhost:52448 | masters | Sleep   |  232 |       | NULL             |
| 301 | mastersuser | localhost:52449 | masters | Sleep   |  231 |       | NULL             |
| 308 | mastersuser | localhost:52453 | masters | Sleep   |  219 |       | NULL             |
| 315 | mastersuser | localhost:52457 | masters | Sleep   |  210 |       | NULL             |
| 316 | mastersuser | localhost:52458 | masters | Sleep   |  210 |       | NULL             |
| 317 | mastersuser | localhost:52459 | masters | Sleep   |  210 |       | NULL             |
| 319 | mastersuser | localhost:52460 | masters | Sleep   |  210 |       | NULL             |
| 330 | mastersuser | localhost:52468 | masters | Sleep   |  196 |       | NULL             |
| 331 | mastersuser | localhost:52469 | masters | Sleep   |  196 |       | NULL             |
...
| 436 | mastersuser | localhost:52547 | masters | Sleep   |   47 |       | NULL             |
| 468 | root        | localhost       | masters | Query   |    0 | NULL  | SHOW processlist |
+-----+-------------+-----------------+---------+---------+------+-------+------------------+


After a while, the sleep processes are gone.

Should I regard this as a problem?
To me, it seems like an application connecting using the 'mastersuser' account is not properly closing connections, so yes I'd say it's a problem. They likely disappear after reaching the wait_timeout or interactive_timeout setting.