slapd memory usage

["A. Schulze" <sca@andreasschulze.de>]

Hello,

A friend told me about his findings on slapd memory usage.

setup:
	openldap-2.4.47
	back_mdb
	slapd running as PID 1 inside a docker container
	docker host and docker conatiner based on Debian 9 / 64 bit

finding:
	with minimal / trivial data slapd consume happily 20% of available phys. memory:

# top -p $( pidof slapd)
top - 21:47:10 up 10 days, 10 min,  5 users,  load average: 0,06, 0,08, 0,09
Tasks:   1 total,   0 running,   1 sleeping,   0 stopped,   0 zombie
%Cpu(s):  0,9 us,  0,5 sy,  0,0 ni, 97,2 id,  1,3 wa,  0,0 hi,  0,1 si,  0,0 st
KiB Mem :  3926252 total,   142672 free,  1517516 used,  2266064 buff/cache
KiB Swap:   975868 total,   913316 free,    62552 used.  2065320 avail Mem 

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND                                  
 2604 165534    20   0 1039308 732000   5628 S   0,0 18,6   0:00.38 slapd  

workaround:
	https://discuss.linuxcontainers.org/t/empty-openldap-slapd-consuming-800-mb-memory-on-lxc-solved/1022
	-> limit open files to 1024

# top -p $( pidof slapd)
top - 21:49:16 up 10 days, 12 min,  5 users,  load average: 0,07, 0,11, 0,10
Tasks:   1 total,   0 running,   1 sleeping,   0 stopped,   0 zombie
%Cpu(s):  1,7 us,  0,6 sy,  0,0 ni, 90,6 id,  7,1 wa,  0,0 hi,  0,0 si,  0,0 st
KiB Mem :  3926252 total,   863500 free,   796492 used,  2266260 buff/cache
KiB Swap:   975868 total,   913320 free,    62548 used.  2786248 avail Mem 

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND                                  
 2993 165534    20   0   48864   7820   5684 S   0,0  0,2   0:00.01 slapd

as far as I can tell from a short test there are no functional drawbacks.

Any idea why the memory usage is so different?

Andreas