Re: Slapd running very slow

[Geoff Swan <gswan3@bigpond.net.au>]

On 2015-04-22 6:04 AM, Howard Chu wrote:
> Brian Reichert wrote:
>> On Tue, Apr 21, 2015 at 08:23:31AM -0700, Quanah Gibson-Mount wrote:
>>> --On Tuesday, April 21, 2015 11:54 AM -0400 Brian Reichert
>>> <reichert@numachi.com> wrote:
>>>> What does your config file look like?
>>>>
>>>> In particular, what does this setting look like for you:
>>>>
>>>>   # Threads - four per CPU
>>>>   threads 8
>>>
>>> According to his summary, he's using 48 threads.
>>
>> Thanks for pointing that out; I should finish my coffee before
>> posting. :)
>>
>>> 4 per CPU/core was a good
>>> rule of thumb with bdb/hdb.  So far in playing with back-mdb, it's
>>> seemed
>>> closer to 2 per CPU/core for me in benchmarking.
Interesting. What is the relationship between the number of threads and
the number of concurrent bind operations?
If I have, say, 500 clients wanting access to perform simple
authentication/bind and perform some read/write operation, how is this
usually handled within slapd?

>>
>> Useful to note.  Has this detail ended up in any docs yet?
>
> No, nor should it. Performance depends on system environment and
> workload - the right value is one that each site must discover for
> themselves in their own deployment.
>

Are there any clues about key factors affecting this? Linux, in this
case, has vm.swappiness set to 10, vm.dirty_ratio at 12 and
vm.dirty_background at 3. However I've noticed that when dirty pages are
flushed to disc, the system stalls. And that operation appears to take a
relatively long time. Disc write speed should be close to 130MB/s (file
copy, dd test etc) however it appears to be much slower than this with
the page flush.