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(ITS#7567) Alias dereferencing slowness

Full_Name: Luca Scamoni
Version: 2.4.35
OS: Linux
URL: ftp://www.sys-net.it/alias-deref-ITS2.tar.gz
Submission from: (NULL) (

Investigating alias dereferencing slowness on a customer production system I
came upon a suspect behaviour with back-hdb/bdb.
It seems that slapd, when dereferencing, instead of looking for the exact
aliased DN, starts scanning more entries than needed (at least this is what I
can tell looking to the logs set to log anything)
On the customer system, with over 700,000 entries, the time taken to perform a
simple search with alias dereferencing for a single entry, takes as much as
performing a full ldapsearch of the entire ldap tree.
To reproduce I created a small testcase (that I can't upload because there's no
space left on ftp.openldap.org/incoming). The test case contains also the log
and the operations performed on test data to show the issue.
I tested with openldap 2.4.23, 2.4.31 and 2.4.35. The issue is present in all
versions but seems to manifest itself only with back-bdb/hdb. Back-mdb seems not
to show the issue (even looking at the logs) but right now, moving to back-mdb
is not something the customer is ready to take.