slapd 100% CPU usage !

[Jehan PROCACCIA <Jehan.Procaccia@int-evry.fr>]

Hello

I am running openldap 2.1.9, with bdb-backend (4.1.24). After starting 
slapd, it takes nearly all the CPU usage :-( .

$ top
CPU states: 50.1% user, 49.8% system,  0.0% nice,  0.0% idle
Mem:   255300K av,  246444K used,    8856K free,       0K shrd,   19044K 
buff
Swap:  265032K av,   30992K used,  234040K free                  124604K 
cached

  PID USER     PRI  NI  SIZE  RSS SHARE STAT %CPU %MEM   TIME COMMAND
 1939 ldap      25   0  4260 4260  3080 R    96.0  1.6   5:43 slapd

I am wondering what slapd is doing so I run a strace:

$ strace -p 1939
sched_yield()                           = 0
sched_yield()                           = 0
sched_yield()                           = 0
....
infinite lines like these .

I did recreate my base from a ldif file (extracted with slapcat from a 
2.0.25 openldap ldbm with berkeley database) and inserted with slapadd .

As it first took nearly an hour to do the slapadd, I did as recommended 
in the list, create a DB_CONFIG file to optimise slapadd operation:

[root@corbeau /var/lib/ldap/int]
$ cat DB_CONFIG
#set the logfile size to 100MB.
set_lg_max 104857600
#set the in-memory log buffer size
set_lg_bsize 262144
#temporary while we're slapadding the database
set_flags DB_TXN_NOSYNC
#set the (per db?) cachesize to 0GB + X bytes, split into N pieces of memory
set_cachesize 0 209715200 2

Now I wonder if my problems comes from here ? I also see that we can put 
these BDB options in slapd.conf file (cachesize <integer>, checkpoint 
<kbyte> <min> , dbnosync ..) however they doesn't seem to be taken into 
account while slapadding !? I really needed to create the DB_CONFIG file 
to reduce time of insertion from 50 minutes to 45 seconds !.

What causes slapd to use 100% of CPU?
How should I optimize BDB performance (from DB_CONFIG file or slapd.conf) ?
Are the problems link ?

thanks.