What were you trying to do that didn't work?

When nsslapd-mdb-max-dbs is set to 0, DS autotunes number of sub-dbs, but it's not optimal, as it prevents creating new backends.

What is the impact of this issue to you?

Please provide the package NVR for which the bug is seen:

389-ds-base-2.5.2-2.el9_5.x86_64

How reproducible is this bug?:

Always

Steps to reproduce

1. Create a new instance with the MDB backend and default suffix
2. Set autotuning for mdb-max-dbs and restart the server

   dsconf localhost backend config set --mdb-max-dbs 0
   dsctl localhost restart
   

3. Check that MDB environment was created with max database instances=128 and check that 36 instances were consumed (1 by __DBNAMES, 4 by @long-entryrdn, ancestorid, id2entry, replication_changelog, and 31 by default indexes).

   dbscan -D mdb -S /var/lib/dirsrv/slapd-localhost/db/ | grep 'Database entries:'
   

4. Create new backend and restart the server to recalculate the number of max dbs

   for i in $(seq 1 20); do dsconf localhost backend create --suffix=dc=test$i --be-name=test$i --create-suffix --create-entries; dsctl localhost restart; grep instances /var/log/dirsrv/slapd-localhost/errors | tail -n 1; dbscan -D mdb -S /var/lib/dirsrv/slapd-localhost/db/ | grep 'Database entries:'; done
   

Expected results

nsslapd-mdb-max-dbs is correctly recalculated and has enough free dbs to create new backend.

Actual results

It fails to add 4th backend, as it's not enough free entries (131-106=25, but at least 35 is required for a new backend).

# for i in $(seq 1 20); do dsconf localhost backend create --suffix=dc=test$i --be-name=test$i --create-suffix --create
-entries; dsctl localhost restart; grep instances /var/log/dirsrv/slapd-localhost/errors | tail -n 1; dbscan -D mdb -S /var/lib/dirsrv/slapd-lo
calhost/db/ | grep 'Database entries:'; done
The database was sucessfully created
Instance "localhost" has been restarted
[22/Oct/2024:07:32:49.915157748 -0400] - INFO - dbmdb_make_env - MDB environment created with max database instances=128.
Database entries: 71
free(): invalid pointer
The database was sucessfully created
Instance "localhost" has been restarted
[22/Oct/2024:07:32:53.742132637 -0400] - INFO - dbmdb_make_env - MDB environment created with max database instances=131.
Database entries: 106
free(): invalid pointer
Error: -1 - Can't contact LDAP server - [] - add_ext_s((dn: dc=test3
dc: test3
description: dc=test3
objectclass: top
objectclass: domain

,),{'serverctrls': None, 'clientctrls': None, 'escapehatch': 'i am sure'}) on instance localhost