serious concurrecy problem openldap on redhat AS

[Maxi lubian <maxi.lubian@it.gu.se>]

Hello!

We are experience serious problems with our OpenLDAP on our
Linux Redhat AS EE 3.0.
We run an openldap v 2.0.27 on a dual machine with 2.5 GB memory.

We have 80.000 entries in a ldbm backend database and cant make
search and modify cuncurrently. This causes serious problems when large
reads are made that take aprox 4-5 min. During those reads we cant make any
writes and the client that tries to do so hangs until the read is finished.


We tried with "concurrency" and the "threads" directives in the 
slapd.conf but with no reslut

The slapd.conf file
--------------------------------------------------------
# See slapd.conf(5) for details on configuration options.
# This file should NOT be world readable.
#
include         /etc/openldap/schema/core.schema
include         /etc/openldap/schema/cosine.schema
include         /etc/openldap/schema/inetorgperson.schema
include         /etc/openldap/schema/nis.schema
include         /etc/openldap/schema/eduperson.schema
include         /etc/openldap/schema/noreduperson.schema

# Define global ACLs to disable default read access.

# Do not enable referrals until AFTER you have a working directory
# service AND an understanding of referrals.
#referral       ldap://root.openldap.org

#loglevel 256
loglevel 0
sizelimit 950000

concurrency 25
threads 25

pidfile         /var/run/slapd.pid
argsfile        /etc/openldap/slapd.args

TLSVerifyClient         no
TLSCipherSuite          HIGH:MEDIUM: +TLSv1 +SSLv2 +SSLv3
TLSCertificateFile      /etc/openldap/ldap.crt
TLSCertificateKeyFile   /etc/openldap/ldap.key
TLSCACertificateFile    /etc/openldap/CA.crt

#DB def
database        ldbm
suffix          "dc=mydomain,dc=com"
rootdn          "cn=adm,dc=mydomain,dc=com"
rootpw          xxxxxxxxxxx
directory       /data/openldap/ldap-gu

cachesize   1000000
dbcachesize 1020000000


index   objectClass,member,norEduPersonNIN     eq
index   uid,cn,sn,givenName,mail,description,o,ou eq,sub


access filter ....
--------------------------------------------------------------------------------
end


We have also checked the slapd for linked in libraries and that pthread 
lib  was included.
checked that openldap is compiled with --with-thead flag, which it was.

linked libraies:
]# ldd /usr/sbin/slapd
       libsasl.so.7 => /usr/lib/libsasl.so.7 (0x0020a000)
       libkrb5.so.3 => /usr/kerberos/lib/libkrb5.so.3 (0x00df5000)
       libk5crypto.so.3 => /usr/kerberos/lib/libk5crypto.so.3 (0x00111000)
       libcom_err.so.3 => /usr/kerberos/lib/libcom_err.so.3 (0x00efe000)
       libssl.so.4 => /lib/libssl.so.4 (0x00bda000)
       libcrypto.so.4 => /lib/libcrypto.so.4 (0x00216000)
       libcrypt.so.1 => /lib/libcrypt.so.1 (0x00121000)
       libnsl.so.1 => /lib/libnsl.so.1 (0x009ba000)
       libresolv.so.2 => /lib/libresolv.so.2 (0x004ba000)
       libdl.so.2 => /lib/libdl.so.2 (0x00b0f000)
       libpthread.so.0 => /lib/tls/libpthread.so.0 (0x0046f000)
       libltdl.so.3 => /usr/lib/libltdl.so.3 (0x0032d000)
       libwrap.so.0 => /usr/lib/libwrap.so.0 (0x00d87000)
       libc.so.6 => /lib/tls/libc.so.6 (0x00334000)
       libgdbm.so.2 => /usr/lib/libgdbm.so.2 (0x00f2e000)
       libpam.so.0 => /lib/libpam.so.0 (0x00c49000)
       libgssapi_krb5.so.2 => /usr/kerberos/lib/libgssapi_krb5.so.2 
(0x00ada000)
       libz.so.1 => /usr/lib/libz.so.1 (0x009a5000)
       /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x00d39000)
       liblaus.so.1 => /lib/liblaus.so.1 (0x00f0b000)


We hope that somebody knows a solution or had experienced the same 
problem. I read the openldap lits archives but found only a problem with 
concurrency in openldap2.0.21.. Not in later versions... Is this a 
problem och have we misconfiured our openldap /Linux environment?

Hope any has the the time to answer och look into it.

Best regards Maximiliano