slapadd performance degradation from 2.3.43 to 2.4.12

[Ralf Haferkamp <rhafer@suse.de>]

Hi,

While doing a few slapadd testruns comparing the RE23 with the RE24 version I 
ran into a strange issue. I ran test with different LDIFs (100k, 500k and 
1000k Entries) and especially with the 500k and 1000k LDIF, slapadd from 
2.3.43 was significantly faster than the 2.4.12 version.

2.3.43 loaded the 500k database in 13m54s while it took 33m49s with 2.4.12.
The 1000k testcase to 29m41s on 2.3 (still faster than the 500k on 2.4). I 
didn't finish the 2.4 run with the 1000k database I stopped it after about an 
hour.

I used exactly the same configuration on exactly the same hardware/os for the 
tests (a HP Proliant DL 580 G3 with 4 3.33GHz Xeons, 8GB of RAM, SLES10-SP2, 
ext3 filesystem). BerkelyDB Version was 4.5.20 with the following DB_CONFIG:

set_cachesize 0 4294967295 1
set_lg_regionmax 262144
set_lg_bsize 2097152

cachesize in slapd.conf was large enough to hold the entire database and tool-
threads was set to 4.

I did some profiling (with valgrinds callgrind tool) to find out where all the 
time is spend and it revealed that 2.4 spend a significantly larger amount of 
systime in the pwrite() function than 2.3. Most of that seemed to come from 
the bdb_tool_trickle_task() that calls libdb's memp_trickle() function.
Just to verify this I ran a testbuild with the trickle_task disabled(). And 
slapadd's performance was back to a normal level, comparable to the 2.3.43 
release.

AFAIK the trickle_task() was introduced into 2.4 to increase slapadd 
throughput but has exactly the opposite effect on my test system. Did anybody 
else make similar experiences? Or do you see anything thats obviously wrong 
with my testcases?

-- 
Ralf