killall requires strict match, i.e. "clickhouse-server" not
"clickhouse":
2021-12-03 05:24:56 + env kill -- -21700
2021-12-03 05:24:56 kill: (-21700): No such process
2021-12-03 05:24:56 + killall clickhouse
2021-12-03 05:24:56 clickhouse: no process found
2021-12-03 05:24:56 + echo Servers stopped.
2021-12-03 05:24:56 Servers stopped.
2021-12-03 05:24:56 + analyze_queries
$ tail -n1 *-server-log.log
==> left-server-log.log <==
2021.12.03 05:26:59.530647 [ 450 ] {} <Trace> SystemLog (system.asynchronous_metric_log): Flushed system log up to offset 1668052
==> right-server-log.log <==
2021.12.03 05:27:20.873136 [ 466 ] {} <Trace> SystemLog (system.metric_log): Flushed system log up to offset 9605
==> setup-server-log.log <==
2021.12.03 02:47:14.844395 [ 96 ] {} <Information> Application: Child process exited normally with code 0.
As you can see killall instantly fails with no such process, while this
cannot be true since it was there, and also according to logs there were
messages after running analyze_queries() from compare.sh
This should fix problems like in [1].
[1]: https://clickhouse-test-reports.s3.yandex.net/32080/344298f4037f88b114b8e798bb30036b24be8f16/performance_comparison/report.html#fail1
Recently (#32094) test database had been overlapped, and random prefix
for database had been increased from 6 to 8.
But actually 6 bytes for random prefix should be enough (with existing
alphabet (0-9a-z) it is 36**6=2'176'782'336), and the real reason of
this overlap is that random generator by default uses shared state [1]:
The functions supplied by this module are actually bound methods of
a hidden instance of the random.Random class. You can instantiate your
own instances of Random to get generators that don’t share state.
[1]: https://docs.python.org/3/library/random.html
I've played a little bit with random in python, and using default random
generator it generates non-unique strings pretty fast, just in a few
runs, but using SystemRandom (that uses /dev/urandom) it takes ~1 minute.
Test:
```sh
$ while /tmp/test.py | LANG=c sort -S5G | LANG=c uniq -d | tee /dev/stderr | wc -l | fgrep -q -x -c 0; do :; done
```
```python
#!/usr/bin/env python3
import multiprocessing
import string
import random
def random_str(length=6):
alphabet = string.ascii_lowercase + string.digits
return ''.join(random.SystemRandom().choice(alphabet) for _ in range(length))
def worker(_):
print(random_str())
with multiprocessing.Pool(processes=2) as pool:
pool.map(worker, range(0, int(10e3)))
```
So let's switch to SystemRandom and use 6-byte prefix.
