[Serusers] SER data model discussion - developers please read
Greger V. Teigre
greger at teigre.com
Mon Dec 3 10:25:31 CET 2007
Dear Mahatma,
If you want to engage the developers, you will have to subscribe to
serdev, as many of the developers don't follow serusers.
I have not participated in SER's 2.0 data model, but my initial take on
your suggestion is the following:
With all respect, I believe you may have misunderstood what Tom is
addressing in his discussion. He targets a generic database model built
around attribute value pairs. This is not the case for SER, on the
contrary, SER's new data model is much sounder from a db perspective
(than 0.8 and 0..9) and is built around the uid and did as unique
identifiers. Queries will through joins across the tables construct the
needed data in a very efficient manner, as uid and did are indexed and
where the queries will use uid and did in the where clause. Without
having checked, I assume the tables have been normalized just as they
should (i.e. splitting them up).
The attribute-value pairs you are referring to are not part of the core
data model (which Tom covers), but rather attributes that may be loaded
and made available in ser.cfg through a query created to retrieve the
attributes-value pairs. Without creating a limited set of attributes
that can be supported in ser.cfg, the generic avpairs cannot be avoided.
However, the queries that retrieve avpairs do not use the semantic of
the avpairs to select which avpairs to load, ALL avpairs belonging to a
specific uid and did are loaded at the same time.
Also, I'm afraid this statement is wrong: "It's a better idea from a
database architecture and performance perspective to keep adding columns
into that table for data that has a 1 to 1 relationship with a user."
This is exactly how you should not do it if you have complex data
relationships that need to be represented and retrieved without
duplicating data.
Does this answer alleviate your fears?
If not, please subscribe to serdev and post your comment there to engage
people closer to the design of the database.
g-)
X Z wrote:
> Hi All,
> This is specifically for the SER/OpenSER developers, but I'm not a
> serdev list member so I'm posting here.
>
> I've been using SER since version 0.8.X and I'm still running 0.8.14
> production for my company PBX to this day.
>
> I was very excited as version 2 became a release candidate and I
> downloaded it for testing. I was pretty disappointed with one aspect
> of the new data model and I'm requesting that the developers consider
> a further revision on the data model.
>
> Basically, taking all fields out of the subscriber table like
> Last_name, first_name, email, timezone, rpid/asserted identity, etc,
> etc is not the greatest idea. It's a better idea from a database
> architecture and performance perspective to keep adding columns into
> that table for data that has a 1 to 1 relationship with a user, and
> that is common in > 90% of SER's use cases ( i.e. corporate,
> carrier/VSP.) I would suggest adding voicemail_password, and maybe
> every other field that is being added into the default attributes
> script that I saw in CVS recently. If you already know what attributes
> a user has (and they have a 1 to 1 relationship), then its far better
> from a db performance perspective to keep these attributes in the user
> table. I know that the code becomes more complicated, but I think it
> may be a tradeoff worth discussing.
>
> See this discussion (
> http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:10678084117056
> ) between Oracle users and Tom, (an Oracle engineer/architect.) The
> full text of this discussion is very informative and I highly
> recommend people read it through.
>
> Tom's conclusion is that the type of data model being discussed, and
> now being used in SER fails for all but the most trivial of
> applications. Maybe SER *by itself* qualifies as "trivial" from a
> database architect's perspective, but think about things like Asterisk
> integration, which is quite common. You quickly run into some very
> nasty queries . . .
>
> Please note that I am not a software developer nor a database
> engineer, just a user who reads a lot, so I'm open to being the
> ignorant one here, but I thought that this should be discussed among
> users and developers.
>
> Thanks for considering,
> Mahatma
>
> http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:10678084117056
> <http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:10678084117056>
>
>
> The following is an excerpt from the above link:
>
> Here is a excerpt from my forthcoming book where I talk about this (and show you how
> ugly, hard and inefficient queries against your very flexible model will be)
>
>
>
>
> (2)Do not use Generic Data Models
>
> Frequently I see applications built on a generic data model for "maximum flexibility" or
> applications built in ways that prohibit performance. Many times - these are one in the
>
> same thing! For example, it is well known you can represent any object in a database
> using just four tables:
>
> Create table objects ( oid int primary key, name varchar2(255) );
>
> Create table attributes
>
> ( attrId int primary key, attrName varchar2(255),
> datatype varchar2(25) );
>
> Create table object_Attributes
> ( oid int, attrId int, value varchar2(4000),
> primary key(oid,attrId) );
>
> Create table Links ( oid1 int, oid2 int,
>
> primary key (oid1, oid2) );
>
>
> That's it - no more CREATE TABLE for me! I can fill the attributes table up with rows
> like this:
>
> insert into attributes values ( 1, 'DATE_OF_BIRTH', 'DATE' );
>
> insert into attributes values ( 2, 'FIRST_NAME', 'STRING' );
> insert into attributes values ( 3, 'LAST_NAME', 'STRING' );
> commit;
>
>
> And now I'm ready to create a PERSON record:
>
>
> insert into objects values ( 1, 'PERSON' );
> insert into object_Attributes values( 1, 1, '15-mar-1965' );
> insert into object_Attributes values( 1, 2, 'Thomas' );
> insert into object_Attributes values( 1, 3, 'Kyte' );
>
> commit;
>
> insert into objects values ( 2, 'PERSON' );
> insert into object_Attributes values( 2, 1, '21-oct-1968' );
> insert into object_Attributes values( 2, 2, 'John' );
> insert into object_Attributes values( 2, 3, 'Smith' );
>
> commit;
>
> And since I'm good at SQL, I can even query this record up to get the FIRST_NAME and
> LAST_NAME of all PERSON records:
>
> ops$tkyte at ORA920> select
> max( decode(attrName, 'FIRST_NAME', value, null )) first_name,
>
> 2 max( decode( attrName, 'LAST_NAME', value, null ) ) last_name
> 3 from objects, object_attributes, attributes
> 4 where attributes.attrName in ( 'FIRST_NAME', 'LAST_NAME' )
>
> 5 and object_attributes.attrId = attributes.attrId
> 6 and object_attributes.oid = objects.oid
> 7 and objects.name <http://objects.name> = 'PERSON'
> 8 group by objects.oid
>
> 9 /
>
> FIRST_NAME LAST_NAME
> -------------------- --------------------
> Thomas Kyte
> John Smith
>
>
> Looks great, right? I mean, the developers don't have to create tables anymore, we can
>
> add columns at the drop of a hat (just requires an insert into the ATTRIBUTES table). The
> developers can do whatever they want and the DBA can't stop them. This is ultimate
> "flexibility". I've seen people try to build entire systems on this model.
>
>
> But, how does it perform? Miserably, terribly, horribly. A simple "select first_name,
> last_name from person" query is transformed into a 3-table join with aggregates and all.
> Further, if the attributes are "NULLABLE" - that is, there might not be a row in
>
> OBJECT_ATTRIBUTES for some attributes, you may have to outer join instead of just joining
> which in some cases can remove more optimal query plans from consideration.
>
> Writing queries might look pretty straightforward, but it's impossible to do in a
>
> performant fashion. For example, if we wanted to get everyone that was born in MARCH or
> has a LAST_NAME = 'SMITH', we could simply take the query from above and just wrap an
> inline view around that:
>
>
>
> ops$tkyte at ORA920> select *
> 2 from (
> 3 select
> max(decode(attrName, 'FIRST_NAME', value, null)) first_name,
> 4 max(decode(attrName, 'LAST_NAME', value, null)) last_name,
>
> 5 max(decode(attrName, 'DATE_OF_BIRTH', value, null))
> date_of_birth
> 6 from objects, object_attributes, attributes
> 7 where attributes.attrName
> in ( 'FIRST_NAME',
> 'LAST_NAME', 'DATE_OF_BIRTH' )
> 8 and object_attributes.attrId = attributes.attrId
> 9 and object_attributes.oid = objects.oid
>
> 10 and objects.name <http://objects.name> = 'PERSON'
> 11 group by objects.oid
> 12 )
> 13 where last_name = 'Smith'
> 14 or date_of_birth like '%-mar-%'
>
> 15 /
>
> FIRST_NAME LAST_NAME DATE_OF_BIRTH
> -------------------- -------------------- --------------------
> Thomas Kyte 15-mar-1965
> John Smith 21-oct-1968
>
>
> So, it looks "easy" to query, but think about the performance! If you had a couple
> thousand OBJECT records, and a couple tens of thousands of OBJECT_ATTRIBUTES - Oracle
> would have to process the entire inner group by query first and then apply the WHERE
>
> clause.
>
> This is not a made up data model, one that I crafted just to make a point. This is an
> actual data model that I've seen people try to use. Their goal is ultimate flexibility.
> They don't know what OBJECTS they need, they don't know what ATTRIBUTES they will have.
>
> Well - that is what the database was written for in the first place: Oracle implemented
> this thing called SQL to define OBJECTS and ATTRIBUTES and lets you use SQL to query
> them. You are trying to put a generic layer on top of a generic layer - and it fails each
>
> and every time except for the most trivial of applications.
>
>
> ------------------------------------------------------------------------
>
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>
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