Bug #20629 DBD::mysql::db do failes when too many concurrenct connections

Description:
When we run a benchmark script which need for the PT Workshop. It gives an error with too many concurrent connections.

How to repeat:
# perl benchmark-sql.pl --flush=0 -c 1 -n 10000 --schema=world -e "select 1"
Total Time is: 1.0333
Number of Iterations: 10000
Number of Clients: 1

  #   Time/Query  Total Time  Query
 ---  ----------  ----------  -----
  1.     0.00010     1.03315  select 1

  1. select 1

# perl benchmark-sql.pl --flush=0 -c 5 -n 2000 --schema=world -e "select 1"
ERROR processing SQL statement #1:

select 1

DBD::mysql::db do failed: Lost connection to MySQL server during query at benchmark-sql.pl line 132.
 at benchmark-sql.pl line 132
        eval {...} called at benchmark-sql.pl line 132

# perl benchmark-sql.pl --flush=0 -c 25 -n 400 --schema=world -e "select 1"
DBD::mysql::db do failed: Lost connection to MySQL server during query at benchmark-sql.pl line 112.
 at benchmark-sql.pl line 112

We were able to reproduce on different machines, on linux, win...

Thank you for a problem report. Plwase, specify the exact version of DBD::mysql used.

perl -MDBD::mysql -e 'print "$DBD::mysql::VERSION\n";'
2.9004

But in the Workshop yesterday we downloaded the newest version from the web I think...

I installed now the brand new DBI and DBD and it still fails:

# perl --version

This is perl, v5.8.6 built for i586-linux-thread-multi
...

# perl -MDBI -e'print "$DBI::VERSION\n";'
1.51

# perl -MDBD::mysql -e'print "$DBD::mysql::VERSION\n";'
3.0006

Please, try with -n 100. Check max_connections setting on all the MySQL servers you had used. It is 100 by default...

No difference changing -n to 100. As soon as I set -c bigger than 1 it becomes unstable. As bigger as -c is as more unstable it gets and above -c 8 or 16 it does not work anymore.
I have the intention that when I set the thread_cache > 0 it is a little more stable. But only a little...

I can try it also on my Windows. But only if it realy helps you (win igigit!)...

Verified just as described with your test script, with 5.0.25-BK and DBD::mysql 3.0006 on Linux:

openxs@suse:~/dbs/5.0> perl benchmark-sql.pl --user=root --host='127.0.0.1' --f
lush=0 -c 5 -n 10 --schema=test -e "select 1"
DBD::mysql::db do failed: Lost connection to MySQL server during query at benchm
ark-sql.pl line 112.
 at benchmark-sql.pl line 112
openxs@suse:~/dbs/5.0> perl benchmark-sql.pl --user=root --host='127.0.0.1' --f
lush=0 -c 5 -n 1 --schema=test -e "select 1"
Total Time is: 0.1550
Number of Iterations: 1
Number of Clients: 5

  #   Time/Query  Total Time  Query
 ---  ----------  ----------  -----
  1.     0.03097     0.15484  select 1

  1. select 1

openxs@suse:~/dbs/5.0> perl benchmark-sql.pl --user=root --host='127.0.0.1' --f
lush=0 -c 5 -n 2 --schema=test -e "select 1"
DBD::mysql::db do failed: Lost connection to MySQL server during query at benchm
ark-sql.pl line 112.
 at benchmark-sql.pl line 112
openxs@suse:~/dbs/5.0> perl benchmark-sql.pl --user=root --host='127.0.0.1' --f
lush=0 -c 1 -n 2 --schema=test -e "select 1"
Total Time is: 0.0068
Number of Iterations: 2
Number of Clients: 1

  #   Time/Query  Total Time  Query
 ---  ----------  ----------  -----
  1.     0.00338     0.00676  select 1

  1. select 1

openxs@suse:~/dbs/5.0> perl benchmark-sql.pl --user=root --host='127.0.0.1' --f
lush=0 -c 1 -n 200 --schema=test -e "select 1"
Total Time is: 0.1830
Number of Iterations: 200
Number of Clients: 1

  #   Time/Query  Total Time  Query
 ---  ----------  ----------  -----
  1.     0.00091     0.18290  select 1

  1. select 1

openxs@suse:~/dbs/5.0> perl benchmark-sql.pl --user=root --host='127.0.0.1' --f
lush=0 -c 2 -n 200 --schema=test -e "select 1"
Total Time is: 0.4189
Number of Iterations: 200
Number of Clients: 2

  #   Time/Query  Total Time  Query
 ---  ----------  ----------  -----
  1.     0.00105     0.41879  select 1

  1. select 1

openxs@suse:~/dbs/5.0> perl benchmark-sql.pl --user=root --host='127.0.0.1' --f
lush=0 -c 5 -n 200 --schema=test -e "select 1"
ERROR processing SQL statement #1:

select 1

DBD::mysql::db do failed: Lost connection to MySQL server during query at benchm
ark-sql.pl line 132.
 at benchmark-sql.pl line 132
        eval {...} called at benchmark-sql.pl line 132

Thank you for the report.

We don't work on DBD::mysql bugs anymore. All its bugs should go to CPAN: https://rt.cpan.org/Public/Dist/Display.html?Name=DBD-mysql

I re-submitted your report to https://rt.cpan.org/Public/Bug/Display.html?id=83520
Please subscribe to the new report on CPAN and work with DBD::mysql developers in case if they need additional details.

I did not find a way to re-send attached test case privately. Please, remove all sensitive data and attach it to CPAN yourself.