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Re: Help: Slow LDAP search with high %iowait
Hi,
Victor <victorfuman@yahoo.com> writes:
> Would you folks mind sharing some thoughts/ideas on this? Thanks a lot!
>
>
> --- On Mon, 9/8/08, Victor <victorfuman@yahoo.com> wrote:
>
>> From: Victor <victorfuman@yahoo.com>
>> Subject: Help: Slow LDAP search with high %iowait
>> To: openldap-technical@openldap.org
>> Date: Monday, September 8, 2008, 5:35 PM
>> Hi ,
>>
>> I did quite a bit reading and research before I send email
>> to this list for help. If I have missed some basic concepts
>> here, please execuse my ignorance. Thanks for your help and
>> time in advance.
did you read
http://www.openldap.org/faq/data/cache/1075.html
>> 1. Summary
>> The initial search in my prototyping with OpenLDAP (slapd +
>> BDB) seemed to be slow. What is the reason and How could I
>> fix it?
>>
>> 2. Configuration
>> 2.1 Environment
>> Linux CentOS, 1 hard disk (therefore unfortunately the BDB
>> transaction logs and database files are written to the same
>> disk), 120GB disk space (80% unused), 1GB RAM, reserved for
>> this prototyping, OpenLDAP 2.3.39 with default BDB
>> installation
add more RAM to your machine
>> 2.2 slapd.conf (modified trivially for discussion
>> purpose)
>> # global configuration
>> loglevel 0
>>
>> # BDB
>> database bdb
>> suffix "dc=test,dc=dummy,dc=com"
>> rootdn
>> "cn=Manager,dc=test,dc=dummy,dc=com"
>> # Cleartext passwords, especially for the rootdn, should
>> # be avoid. See slappasswd(8) and slapd.conf(5) for
>> details.
>> # Use of strong authentication encouraged.
>> rootpw secret
>> # The database directory MUST exist prior to running slapd
>> AND
>> # should only be accessible by the slapd and slap tools.
>> # Mode 700 recommended.
>> directory /usr/local/var/openldap-data
>> #Other DB configuration
>> idlcachesize 60000
>> cachesize 20000
increase cachesize, add dncachsize, man slapd-bdb(5)
>> # Indices to maintain
>> # the indexes are to support search in first name, last
>> name and email for both exact match and wild cards in the
>> end
>> index objectClass eq
>> index gn pres,eq,sub
>> index sn pres,eq,sub
>> index mail pres,eq,sub
>>
>> 2.3 DB_CONFIG (for BDB)
>> set_cachesize 0 52428800 1
>> set_lg_bsize 2097512
>> set_flags DB_LOG_AUTOREMOVE
>> set_lg_regionmax 262144
increase cachesize
>> 2.4 Data setup
>> 2 million records (users with gn, sn, email, mobile, street
>> address, etc. in the BDB; all records are indexed using the
>> index in the above slapd.conf; grouped by the first
>> character of lastName. For example,
>> dn: ou=Z,dc=test,dc=dummy,dc=com
>> objectclass: organizationalUnit
>> ou: Z
>
>> Sample LDIF entry:
>> #Directory Entry
>> dn:
>> uid=ABCDEFGHIJKLMNOPQRSTUVWXYZ123459,ou=F,dc=test,dc=dummy,dc=com
>> objectclass: top
>> objectclass: person
>> objectclass: organizationalPerson
>> objectclass: inetOrgPerson
>> uid: ABCDEFGHIJKLMNOPQRSTUVWXYZ123459
>> ...... (details omitted)
What is the size of id2entry.bdb and all indexed >attribute>.bdb
>> 3. Symptom/Problem
>>
>> It was very slow in the first (fresh) search if I searched
>> by wildcard firstname only like "Larry*" (which
>> returned 478 entries/users). The response time was generally
>> higher than 5 seconds Depending the count of records found,
>> the response time might exceed 20 or even 50 seconds. During
>> the search, the "iostat" result showed +95%
>> %iowait, await was much higher that svctm, the device %util
>> was over 96%. Here is the "iostat" output:
This might depend on disk type, PATA vs. SATA, read ahead abilities
and so on.
>> However, The subsequent search (using the exact search
>> criteria) is much faster (within 200ms). I believe it is
>> because of the cache.
200 ms is not fast enough, depending on network and server load,
respose values of 4 to 10 ms are reasonable.
-Dieter
--
Dieter Klünter | Systemberatung
http://www.dpunkt.de/buecher/2104.html
GPG Key ID:8EF7B6C6
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