some entry lost in openldap (ITS#458)

[zhangby@chinaren.com]

Full_Name: zhang ben yu
Version: 1.2.7 release
OS: linux (kernel 2.2.10)
URL: ftp://ftp.openldap.org/incoming/
Submission from: (NULL) (202.106.6.245)


1.hardware: 1G mem, PIIIXeon, if anything else need to be known, please ask;
2.config file(slapd.conf):
#
# See slapd.conf(5) for details on configuration options.
# This file should NOT be world readable.
#
include         /usr/local/etc/openldap/slapd.at.conf
include         /usr/local/etc/openldap/slapd.oc.conf
schemacheck     off
pidfile         /usr/local/var/slapd.pid
argsfile        /usr/local/var/slapd.args

#######################################################################
# ldbm database definitions
#######################################################################

database        ldbm
#suffix         "dc=your-domain, dc=com"
suffix          "o=XXX, c=XX"
directory       /opt/ldap/db
#readonly on
#rootdn         "cn=root, dc=your-domain, dc=com"
rootdn          "cn=root, o=xxx, c=xx"
rootpw          xxx
# cleartext passwords, especially for the rootdn, should
# be avoid.  See slapd.conf(5) for details.
#defaultaccess   read
defaultaccess   none
access to dn=".*,c=XXX"
        by addr=127\.0\.0\.1 read
        by dn="cn=root, o=xxx, c=XX" write
        by * none
cachesize       100000
dbcachesize     10000000
index   cn      pres,eq,approx,sub
index   pwd     eq
index   objectclass     pres,eq
index   reg_host        pres,eq
index   mailmessagestore        pres,eq
#end
for some reason, I use xxx to replace something:-)

3.some description:
the openldap stores millions of users' information, including cn, pwd, mail,etc.
There are some C programs to search and modify the ldbm through API.
It works well most time,but yesterday an emergency happened. the programs cannot
get some users' information ; I tried ldapsearch , nothing return. Then I use
ldbmcat id2entry.dbb > some_file ; there is nothing about them. At last I tried
to use ldapadd to add the 'lost'information, but it said them exist. So I think
the ldbm file corrupted. 
Any Idea? Any suggestion? Why this happened? How to prevent it? How to deal with
it?
very urgency!
thanks!!