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(ITS#6396) slow reads on slaves after many changes in master

Full_Name: Rolandas Naujikas
Version: 2.4.19
OS: FreeBSD 7.1
URL: ftp://ftp.openldap.org/incoming/
Submission from: (NULL) (

We have a setup of 3 slapd: 2 of them running in mirror mode and last one as a
read-only slave. All entries could fit in the cache (my goal is good read

Usually when master receive only small changes (modify + several adds) - read
performance is OK.

When I do ~5% content change (doing a lot of deletes and adds in short period),
then read performance drops sharply - on master not so much (2x), on slaves
10-20x. In the same time CPU load on slaves when doing read is becoming high
(almost 100%), on master - normal.

It rests in such situation until I restart slave instances, after that all such
performance problems disappears.

By comparison version 2.4.16 didn't show such behavior and for some time (until
2.4.19 was not declared stable) we used this older version.