Windl, Ulrich wrote:

Hi again!

I've implemented a Nagios compatible monitor for the MDB freespace, but I'm trying to understand: The "unused pages" are non-fragmented, obviously The "free pages" may be scattered all over, but are completely free May there exist partially free pages that are not accounted in the monitor info?

No. There is no such thing as a partially free page.

Also for a huge change request are contiguous pages needed, or is only the number of available pages important?

Does MDB care about fragmentation at all?

LMDB is a key/value store, large values are stored on contiguous pages. Fragmentation will affect the search for contiguous pages for large values.

back-mdb may change multiple underlying records for a given LDAP modification. Indices are small, and unaffected by fragmentation. Other things may have varying sizes.

Kind regards, Ulrich Windl

...

-----Original Message----- From: Howard Chu hyc@symas.com Sent: Friday, April 25, 2025 6:16 PM To: Windl, Ulrich u.windl@ukr.de; openldap-technical@openldap.org Subject: [EXT] Re: MDB monitoring: How many free pages actually?

Windl, Ulrich wrote:

...

Hi,

Considering this monitoring information, I wonder:

olmMDBPagesMax: 12800 olmMDBPagesUsed: 9229 olmMDBPagesFree: 3810

...

Is the number of actual free pages 12800 - 9229 + 3810, i.e. "unallocated

(12800 - 9229)" plus "usable" (3810)?

Yes. "Pages Free" are used pages that are reusable.

...

How many free pages are needed before updates stop working?

That depends on the size of an update.

-- -- Howard Chu CTO, Symas Corp. http://www.symas.com Director, Highland Sun http://highlandsun.com/hyc/ Chief Architect, OpenLDAP http://www.openldap.org/project/

From: Clément OUDOT clem.oudot@gmail.com Sent: Wednesday, June 18, 2025 10:41 AM To: Windl, Ulrich u.windl@ukr.de Cc: openldap-technical@openldap.org Subject: [EXT] Re: Re: MDB monitoring: How many free pages actually?

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Le mar. 17 juin 2025 à 09:50, Windl, Ulrich <u.windl@ukr.demailto:u.windl@ukr.de> a écrit : Hi again!

I've implemented a Nagios compatible monitor for the MDB freespace, but I'm trying to understand: The "unused pages" are non-fragmented, obviously The "free pages" may be scattered all over, but are completely free May there exist partially free pages that are not accounted in the monitor info? Also for a huge change request are contiguous pages needed, or is only the number of available pages important?

Does MDB care about fragmentation at all?

Hello Ulrich,

you can also give a look to this Nagios plugin: https://ltb-project.org/documentation/check_lmdb_usage.html

It uses mdb_stats command. [Windl, Ulrich] I wanted to try that first, too, but in SLES15 SP6 that command isn’t available…

Clément.