Generally the advice is:
* autotune everything * handtune everything.
IMO, autotuning is better (but I did write it, so I'm biased), and don't touch the "split" because we've seen lots of communication issues and challenges trying to educate about how the query processing works in the server core.
I can write a longer piece of how all the query server layers fit together and what each tuning does, but I won't be able to for a few weeks (I'm traveling).
On 17 Jul 2019, at 02:30, Paul Whitney paul.whitney@chesapeake-it.com wrote:
Hi Mark,
What I was referring to is:
"nsslapd-cache-autosize-split The value sets the percentage of RAM that is used for the database cache. The remaining percentage is used for the entry cache. More than 512 MB RAM database cache do not improve the performance. Therefore, the database cache is limited to 512 MB." - https://access.redhat.com/documentation/en-us/red_hat_directory_server/10/ht... Then further down is a table that tops off at 512MB for dbcache in the same document. But even further down it contradicts by suggesting the results of the dbmon.sh script can provide insight into how much more the dbcache can be to improve performance with the 2.2% free example. All these tuning features are great, but gets confusing when trying to mix and match the best combination of settings. I did go over your recommendations and have settled for now on increasing the dbcache to 5GB. Our consumers are configured with 64GB and the masters 128GB. While the percentage of free space in the dbcache is not optimal (more than 12%), we are achieving a hit ratio of 99%.
It's confusing because we never explain how queries and cache's affect each other in a coherent document ... :) Which is tottaly our fault.
summary version - dbcache will cache the raw pages for bdb (IE indexes, serialised entry pages etc).
entry cahce is deserialised entries in a seperate hashmap internal to the server.
So entries go through:
BDB -> dbcache -> entrycache -> entries in results etc.
You generally want to cache more in the entrycache because the deserialisation between dbcachce -> entrycache is really expensive.
If your entrycache is sized properly, the dbcacche ends up caching index pages instead. This goes through:
BDB -> dbcache -> IDL -> Query processing
There is a "slight" cost from dbccache -> IDL, but not enough to justify a cacche.
So your dbccache becomes an index cache effectively, and as a result, generally is "smaller" because IDLs are very very small - you can probably size what a dbcache should be by listing the content in var/lib/dirsrv/slapd-instance/db/userRoot/*.db, excluding "id2entry". Then add maybe 50% or so to get some breathing room.
You can size your entrycache by looking at the size of the id2entry file, and again, add a bit extra fro breathing room and struct overheads.
Hope that helps - perhaps a future autotuning will do this same process.
Paul M. Whitney, RHCSA, CISSP Chesapeake IT Consulting, Inc. 2680 Tobacco Rd Chesapeake Beach, MD 20732
Work: 443-492-2872 Cell: 410.493.9448 Email: paul.whitney@chesapeake-it.com CONFIDENTIALITY NOTICE The information contained in this facsimile or electronic message is confidential information intended for the use of the individual or entity named above. If the reader of this message is not the intended recipient, or an employee or agent responsible for delivering this facsimile message to the intended recipient, you are hereby notified that any dissemination, or copying of this communication is strictly prohibited. If this message contains non-public personal information about any consumer or customer of the sender or intended recipient, you are further prohibited under penalty of law from using or disclosing the information to any third party by provisions of the federal Gramm-Leach-Bliley Act. If you have received this facsimile or electronic message in error, please immediately notify us by telephone and return or destroy the original message to assure that it is not read, copied, or distributed by others.
From: Mark Reynolds mreynolds@redhat.com Sent: Tuesday, July 16, 2019 9:30 AM To: General discussion list for the 389 Directory server project.; Paul Whitney Subject: Re: [389-users] Recommended SLAPD cache sizes
Hi Paul,
On 7/16/19 9:16 AM, Paul Whitney wrote:
Is there some formula or recommendation on determining what would be the optimal cache settings for a directory server (389-ds of course) with following sizes? I looked at the DS 10 Admin Guide online and am getting conflicting information. But the manual shows a table and suggests that the max size for the cn=config dbcache is 512MB.
There is no limit on the cache size value besides what you are limited to by a unsigned long integer. Do you have a link to where it says 512 MB is a maximum?
But I tried with 5GB and it appears to work fine with it, although over time start to see negative values (prob not enough cache) and roevicts while running the dbmon.sh script.
__db files = ~6GB groupRoot = 1.5GB userRoot = 20GB
What values would yield best performance for:
cn=config dbcache? currently set to 5GB but are still seeing lots of roevicts. As much
userRoot entry cache? currently set to 21GB (hit ratio so far at 95%)
groupRoot entry cache? currently set to 2GB (hit ration so far at 96%)
Virtual machine configured with 8CPU, 128GB RAM. Load is in the low 20's with occasional spikes to high 20's.
If you have 128 GB available to you then I would continue to increase the cache sizes until you get to 99% hit ratio for the two entry caches, and the db cache. Also make sure the DN and NDN caches also have a 99% cache hit ratio:
https://access.redhat.com/documentation/en-us/red_hat_directory_server/10/ht...
https://www.port389.org/docs/389ds/design/normalized-dn-cache.html
I would also look into running the DB on a RAM disk since you have the resources to do so:
https://access.redhat.com/documentation/en-us/red_hat_directory_server/10/ht...
HTH, Mark
Paul M. Whitney, RHCSA, CISSP Chesapeake IT Consulting, Inc. 2680 Tobacco Rd Chesapeake Beach, MD 20732
Work: 443-492-2872 Cell: 410.493.9448 Email: paul.whitney@chesapeake-it.com CONFIDENTIALITY NOTICE The information contained in this facsimile or electronic message is confidential information intended for the use of the individual or entity named above. If the reader of this message is not the intended recipient, or an employee or agent responsible for delivering this facsimile message to the intended recipient, you are hereby notified that any dissemination, or copying of this communication is strictly prohibited. If this message contains non-public personal information about any consumer or customer of the sender or intended recipient, you are further prohibited under penalty of law from using or disclosing the information to any third party by provisions of the federal Gramm-Leach-Bliley Act. If you have received this facsimile or electronic message in error, please immediately notify us by telephone and return or destroy the original message to assure that it is not read, copied, or distributed by others.
389-users mailing list -- 389-users@lists.fedoraproject.org
To unsubscribe send an email to 389-users-leave@lists.fedoraproject.org
Fedora Code of Conduct: https://docs.fedoraproject.org/en-US/project/code-of-conduct/
List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines
List Archives: https://lists.fedoraproject.org/archives/list/389-users@lists.fedoraproject....
--
389 Directory Server Development Team
389-users mailing list -- 389-users@lists.fedoraproject.org To unsubscribe send an email to 389-users-leave@lists.fedoraproject.org Fedora Code of Conduct: https://docs.fedoraproject.org/en-US/project/code-of-conduct/ List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines List Archives: https://lists.fedoraproject.org/archives/list/389-users@lists.fedoraproject....
— Sincerely,
William Brown
Senior Software Engineer, 389 Directory Server SUSE Labs
389-users@lists.fedoraproject.org
-
William Brown