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

[quanah@zimbra.com]

--On Monday, November 23, 2009 9:02 AM +0000 rolnas@gmail.com wrote:

> Full_Name: Rolandas Naujikas
> Version: 2.4.19
> OS: FreeBSD 7.1
> URL: ftp://ftp.openldap.org/incoming/
> Submission from: (NULL) (217.147.36.211)
>
>
> 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 performance).
>
> 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.
>

Can you reproduce this behavior with current CVS checkout of the 
OPENLDAP_REL_ENG_2_4 branch?  I'll note that the entry cache has been 
broken for most of RE2.4, and it is specifically fixed in CVS and will be 
in the upcoming 2.4.20 release.

You fail to note in this ITS any of the following information, which would 
be useful:

(a) Total number of entries in the database

>From slapd.conf/cn=config:

(b) cachesize
(c) idlcachesize
(d) dncachesize

>From the BDB database:

(e) output of du -c -h *.bdb in the database directory
(f) Contents of your DB_CONFIG file


Thanks,
Quanah

--

Quanah Gibson-Mount
Principal Software Engineer
Zimbra, Inc
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