[lisp-snmp] Weak hashtables for OIDs

[John F. <jf...@ms...>]

Dear Chun Tian,

"Chun Tian (binghe)" <bin...@gm...> writes:
> 在 2009-5-11，10:42， John Fremlin 写道：
[...]
>> "Chun Tian (binghe)" <bin...@gm...> writes:
>> [...]
>>> Using a "weak hash table" as a cache for holding SIMPLE-OID instances
>>> which already created in current lisp image, so that few SIMPLE-OID
>>> created when repeat do SNMP-WALK on same MIB node. The key of this
>>> hash table would be a "oid number list" as a list, and the value
>>> would
>>> be the correspond SIMPLE-OID instance.
>>>
>>> Since "weak hash table" is not in CL standard, I'll support only a
>>> few
>>> implementations included at least LispWorks, AllegroCL and SBCL, and
>>> make a new "ASN.1 feature" (OID-CACHE) for this work. Do you think
>>> this features would be useful for you?
>>
>> I think this might be a bad idea and probably will decrease
>> performance
>> on our workload, as we have many OIDs that are never seen again, so
>> putting them into a weak hash-table just causes more problems for the
>> garbage collector (they are difficult to implement efficiently).
>
> OK ... so you don't need it in case you have so many one-time OIDs.

I tried this idea out.

It seems it saved about 10% of memory on Allegro, but did not make any
difference to the speed of our (rather bad) benchmark. 

Maybe it will help, maybe not ;-)

Anyway, here is the patch to use trivial-garbage which has portable weak
hashtables.

(It also fixes some wrong references to #+asn.1-yacc instead of
#+asn.1-features:cl-yacc)