Re: (ITS#6243) back-monitor fails to report entry cache usage

[masarati@aero.polimi.it]

>
>
> --On August 5, 2009 7:17:43 PM +0000 masarati@aero.polimi.it wrote:
>
>>> This may be specific to glued databases (databases rooted at "").
>>
>> The problem could be partially addressed by telling back-bdb (who's
>> maintaining this data in the monitor backend) to check subordinates as
>> soon as it discovers it's a glue instance.  However, this poses two
>> different problems:
>>
>> - is the aggregate information resulting from adding all glued databases
>> cache usage still useful?
>>
>> - what happens if heterogeneous databases are glued?  Significantly,
>> what
>> if the superior database is not bdb/hdb?
>>
>> Probably, the monitor database should also present subordinate databases
>> as separate entries.
>
> Interestingly, in my case, there's only one real database in play for the
> glue as it is, since it's rooted at "".  All other database definitions
> come before it (cn=config, cn=accesslog, cn=monitor).

but... are you actually gluing something?  In any case, this is not
specific to the case of empty suffix in the glue database.  I could easily
reproduce it with a "normal" glued setup, and I was about to start fixing
things when the two above questions came to my mind.

> I'm also curious why back-monitor develops stats for the other caches but
> specifically not for entry cache.

I haven't looked in detail, but it makes sense that some operation occurs
within the glue database which requires caching something, but not
entries.

- The entry cache monitor shows the value of bdb->bi_cache.c_cursize;

- the DN cache monitor shows the value of bdb->bi_cache.c_eiused, which
should be the number of entryinfo structures used;

- the IDL cache monitor shows the value of bdb->bi_idl_cache_size.

In my very simple tests, I only saw something populating the DN cache,
which means some internal operation required to allocate some entryinfo
structures that remain 'round.

In any case, it's only showing information related to its database
structure, it is by no means collecting info from the glued databases.

p.