1 Jun
2005
1 Jun
'05
12:17 a.m.
Zeus Ng wrote:
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.
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.
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-)
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.
For me, integrity is much more important than scalability.
Yes, one have to start with integrity as it cannot be sacrificed...
-----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.
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.
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?!
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