[Serusers] SER usrloc caching, was: SER Reports "out of memory"

[Greger V. Teigre]

Zeus Ng wrote:
> If implemented properly, usrloc cache will no doubt help scaling SER.
> My arguments mainly focus on the DB RW issue. People can decide if
> pure DB usrloc is best for them or not. See inline for comments.
>
>> -----Original Message-----
>
>>> If we are to use pure DB only usrloc. That problem will not happen.
>>
>> Yes, I believe this is the same problem Karl pointed out? In
>> itself it poses
>> an issue, but I think the broader scalability impact is more
>> important.
>>
>
> For me, integrity is much more important than scalability.

Yes, one have to start with integrity as it cannot be sacrificed...

>>> a UA does a REGISTER request every 5 minutes. The REGISTER
>> request will
>>> always behave the same.
>>
>> Well, if the cached usrloc is the same as in the REGISTER
>> request, you don't
>> need to write, do you? This should have a huge impact on the
>> number of
>> necessary writes as without a cache, you must write every time.
>>
>
> How about expire time? Even though contact and receive IP are the
> same, expire time will almost always be different. You can't ignore
> that, can you? Also, if a user has two UA and they register to two
> different SER instances, how are we going to sync the cache without
> writing to DB.

Good points! I forgot about expire time.

>>> For other requests, there is always a DB read within
>>> that 5 minutes interval to populate the cache. Only subsequence
>>> requests
>>> go
>>> through the cache. You may have a difference call patten
>> but I find rarely
>>> two INVITEs to the same UA within 5 minutes interval. After that 5
>>> minutes,
>>> the cache becomes invalid and a DB read is required. Using
>> cache saves
>>> nothing on DB read here. (Obviously you can argue about longer time
>>> between
>>> REGISTER request or contact rarely change with hardphone
>> but the same
>>> principle applies)
>>
>> I'm not sure I understand. The point here is to look at the
>> lifetime of the
>> usrloc, which arguably is (in most cases) far longer than
>> five minutes. I
>> don't follow you in that the cache is invalid after five minutes?!
>>
>
> The life time of UA and it's contact IP may be very long but the life
> time of a register request is limited. The 5 minutes is just an
> example to illustrate that once that register expired, the record
> should not be trust anymore. Only the new register request, with new
> expire time should be used. This is what I mean invalid cache.

Yes, I get it now that I was reminded about the expire time. Valid 
arguments.

>>> Besides, I have good experience with MySQL caching
>>> results. So, DB lookup on every SIP request with proper DB
>> tunning can
>>> achieve similar result.
>>
>> That IS a good point.  However, most of the overhead is not
>> in the actual
>> lookup, but in the call to mysql.  I'm not sure what that
>> overhead is, if it
>
> On local DB server, the overhead is minimal. Unlike PHP, SER opens the
> connection at start up and close it at shutdown. Only the request and
> result go through UNIX socket for each query. This reduce the
> overhead of connect and disconnect which could be heavy. With remote
> DB, the over head is TCP. By using MySQL replication, SER can query
> local DB and leave the TCP overhead to MySQL itself. Going via slow
> WAN link is another issue.

Yes, I guess the iptel guys have some real-life measures they can use in 
deciding upon the best scheme.

Hopefully you're already developed code can be combined with Jan's work. 
Seems like you have spent some time thinking about this. :-D
g-)