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Possible linux tuning for high/constant load connections

OpenLdap software community,

I would like to request your experience for some issue I'm facing trying 
to use jmeter for testing openldap load test.

I made a script that keeps around 10 simultaneous thread connections 
with a ramp time of 1 second. I also use a csv file with the records 
filters so the bind+search+unbind always pass by all records existent in 
the DB.

The issue I'm facing is that after sometime I see some connections being 
refused(no bind) but after sometime the connections start to be accepted 

Analyzing the logs and everything else I could notice the following 
things happening in the system :

1) I see that all connections are accept by the openldap machine and 
then the TIME_WAIT connections start to increase(what make sense);
[root@brtldp11 ~]# netstat -an --protocol=inet -t|wc -l
11636  (around this)

2) After normally the  number of connections(ESTABLISHED, TIME_WAIT, 
etc) increase to values normally over 12,000 then it start to reduce;

3) When these connections start to reduce then I start to see after 
sometime in the output error for jmeter connections ;
<sample t="177" lt="0" ts="1251214974190" s="false" lb="LDAP Bind" 
rc="800" rm="javax.naming.CommunicationException: 
[Root exception is java.net.ConnectException: Cannot assign requested 
address]" tn="Thread Group1 1-2" dt="text" by="409">
&lt;responsemessage&gt;javax.naming.CommunicationException: [Root exception is java.net.ConnectException: Cannot 
assign requested address]&lt;/responsemessage&gt;

4) Also start to see at syslog(LOG4) for openldap(loglevel 2) messages 
like below :
Aug 25 12:42:59 brtldp11 slapd[2720]: connection_read(27): no connection!
Aug 25 12:42:59 brtldp11 slapd[2720]: connection_read(43): no connection!
Aug 25 12:42:59 brtldp11 slapd[2720]: connection_read(28): no connection!
Aug 25 12:42:59 brtldp11 slapd[2720]: connection_read(40): no connection!
Aug 25 12:43:00 brtldp11 slapd[2720]: connection_read(37): no connection!
Aug 25 12:43:00 brtldp11 slapd[2720]: connection_read(30): no connection!
Aug 25 12:43:01 brtldp11 slapd[2720]: connection_read(23): no connection!
Aug 25 12:43:02 brtldp11 slapd[2720]: connection_read(36): no connection!
Aug 25 12:43:02 brtldp11 slapd[2720]: connection_read(41): no connection!

5) The netstat results decrease and all start over again until behavior 
follows all steps again.
[root@brtldp11 ~]# netstat -an --protocol=inet -t|wc -l

I tried to check all tuning parameter I knew and I could not find 
explanation. Some parameters are :
[root@brtldp11 ~]# cat /proc/sys/net/ipv4/ip_local_port_range
32768   61000

[root@brtldp11 ~]# ulimit -a
core file size          (blocks, -c) 0
data seg size           (kbytes, -d) unlimited
scheduling priority             (-e) 0
file size               (blocks, -f) unlimited
pending signals                 (-i) 196607
max locked memory       (kbytes, -l) 32
max memory size         (kbytes, -m) unlimited
open files                      (-n) 65535
pipe size            (512 bytes, -p) 8
POSIX message queues     (bytes, -q) 819200
real-time priority              (-r) 0
stack size              (kbytes, -s) 10240
cpu time               (seconds, -t) unlimited
max user processes              (-u) 196607
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited

I can be sure the test is trying to behave as expected since if I check 
the ESTABLISHED connections I can see the simultaneous connections I 
expect. Like :

[root@brtldp11 ~]# grep ESTA* log1.txt |wc -l

Like I configured in the test for around 10 simultaneous connections 
with 1 second ramp. This was not supposed to be a so high load test but 
this strange behavior is happening.

Even with this small number of connections I have this issue and then 
time by time there are some connections refused. Also when I see this 
situation I try to call ldapsearch and I saw :

[root@brtldp12 jakarta-jmeter-2.3.4]#
[root@brtldp12 jakarta-jmeter-2.3.4]# time ldapsearch -LLL -x -D 
"cn=admin,ou=CONTENT,o=domain,c=fr" -w secret -b 
"ou=CONTENT,o=domain,c=fr" -H ldap:// 
ldap_sasl_bind(SIMPLE): Can't contact LDAP server (-1)

real    0m0.059s
user    0m0.000s
sys     0m0.023s

Running after some seconds I can recover data from this query.

Any ideas? Can this be some openldap configuration? Anyone already 
configured some heavy load test and OS tuning for openldap?

Best Regards,