31 May
2005
31 May
'05
11:48 a.m.
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.
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.
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.
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.
-----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 is very low, you're point hits the "let each
system do what
it's best at..."
More or less.
Zeus