[Serusers] SER data model discussion - developers please read
Jiri Kuthan
jiri at iptel.org
Tue Dec 4 00:30:59 CET 2007
At 18:05 03/12/2007, X Z wrote:
>Hello serdev list,
>
>Please see the thread below started on serusers list.
>
>I do understand the power and design of the new data model and that it does allow the SER Core functionality to be very efficient.
>
>In addition, I definitely agree that of all the scenarios below, data duplication is the best of the undesirable options.
>
>The undesirable options being:
>1. The old data model that didn't support avpairs sufficiently,
>2. The new data model that introduces very inefficient joins and ugly SQL queries in order to create a view to integrate with Asterisk or any other third party application
>3. The new data model that works very well for SER core functionality PLUS a "subscriber" table that includes user data which may duplicated in the avpairs tables.
>
>I wasn't suggesting that the avpairs model was bad, just that the result of the data model as it stands makes it inefficient to integrate with other apps data models (like Asterisk for example.)
>
>I might also suggest that the subscriber table comes back into the core code in an expanded form that covers a high percentage of integration use cases, and that triggers get added in to populate the data which would be duplicated. Users can simply opt to not populate the subscriber table at all and the triggers can be disabled as a db installation option.
The trouble is everyone would wish to have his own subscriber table.
One with call-forwarding, someone else with credit-card number, the other
with subscriber's age, etc. That's clearly a ticket for problems -- we
would have as many data model forks as SER uses outthere.
We could keep at least the codebase under such a model still quite stable
by allowing to interpret any column in the credentials table as AVPs to
be loaded along with credentials. That would be a minor code change, which
would remain stable, and address the desires to load a user record with
all possible stuff. However, migrations of data on any changes would be
sort of painful.
Also for those, who think they need to do something very customized, there
is the db_ops module.
>The great advantage to this is that new users don't have to reinvent the wheel when they want to integrate SER with third party apps to create an "overall system" as sip at arcdiv says below.
>
>I'd be happy to propose a table structure and triggers if this idea gains traction with the development team. We could begin a discussion in the serusers list as to what people would like to see in this table.
>
>I guess I'm suggesting that SER core is great, but coming from the user base, I'd like to see a few more considerations going into how SER will be used. I'm guessing that a vast majority of users will not be using it completely stand alone. Everyone is trying to add value-added services like voicemail, presence, a web interface for users and admin management, etc., etc. Can we come up with a reference model for this and included it in the repository?
Exactly this type of things is what the current data model allows to do easily:
whatever new stuff you have, you are not going to change your data structuctre
and depart from what anyone else is having.
>I think it's very interesting that sip at ardev is commenting that he has to do more modifications to use the new version than he had to do before.
I'm interested in that too and I'm frankly curious what those are.
>I would hope that the development roadmap has improvements in core functionality AND functionality that helps users actually use SER (like simpler integrations and fewer custom mods). Making software simpler to implement always helps encourage adoption and helps increase user base and market share, which supports the success of the project long term.
I'm still not getting what is difficutl here????
-jiri
>Thanks,
>Mahatma
>
>
>On Dec 3, 2007 4:17 AM, SIP <<mailto:sip at arcdiv.com>sip at arcdiv.com> wrote:
>The current data model, while designed to make certain things easier
>DOES indeed encourage data duplication, as, in order to create a unified
>system, most of us will opt to duplicate data into more usable tables.
>When meshing with an overall system, gathering all relevant data for a
>particular substructure or user by using joins is neither speedy
>(especially when the tables get HUGE -- and they very much will) nor
>terribly convenient.
>Of course, data duplication is hardly a cardinal sin, but there's ALWAYS
>a trade off between abstraction and actual functionality. I understand
>the reasons WHY they've chosen the current data model, and to a degree
>it makes sense for the core SER system, but for meshing SER with other
>systems, it's god-awful ugly. :)
>My recommendation, Mahatma, is to AVOID using the new data model for
>anything other than the most basic of SER functionality, or, if you
>gather users in the 50-100,000 user range, your user_attrs table is just
>going to be one ugly, unmanageably large pile of annoyance. Since the
>user_attrs and domain_attrs are designed in part, from what I can tell,
>to make selects more rational and to allow basic SIP flexibility, if you
>don't NEED to keep the data there, don't do it. They could keep
>modifying the data model to suit everyone's tastes, but right now, it's
>designed more to ensure that SER works and works well. Want to store
>user information like a cell phone number and a fax number and a
>timezone and a flag on whether or not that user has DND enabled or has
>access to the PSTN, etc, etc? Keep it elsewhere in a more usable table
>for such purposes.
>As we've begun our testing with SER 2.0, we've had to modify things more
>drastically than we modified them in SER 0.9.6, but in ANY environment,
>you're going to have to modify things to work for you. At least the core
>system is flexible enough to let you tailor things. :)
>N.
>
>Greger V. Teigre wrote:
>> 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>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
>>> <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$tkyte at ORA920 > select
>>> max( decode(attrName, 'FIRST_NAME', value, null )) first_name,
>>>
>>> 2 max( decode( attrName, 'LAST_NAME', value, null ) ) last_name
>>> 3 from objects, object_attributes, attributes
>>> 4 where attributes.attrName in ( 'FIRST_NAME', 'LAST_NAME' )
>>>
>>> 5 and object_attributes.attrId = attributes.attrId
>>> 6 and object_attributes.oid = objects.oid
>>> 7 and <http://objects.name>objects.name <http://objects.name> = 'PERSON'
>>> 8 group by objects.oid
>>>
>>> 9 /
>>>
>>> FIRST_NAME LAST_NAME
>>> -------------------- --------------------
>>> Thomas Kyte
>>> John Smith
>>>
>>>
>>> Looks great, right? I mean, the developers don't have to create tables anymore, we can
>>>
>>> add columns at the drop of a hat (just requires an insert into the ATTRIBUTES table). The
>>> developers can do whatever they want and the DBA can't stop them. This is ultimate
>>> "flexibility". I've seen people try to build entire systems on this model.
>>>
>>>
>>> But, how does it perform? Miserably, terribly, horribly. A simple "select first_name,
>>> last_name from person" query is transformed into a 3-table join with aggregates and all.
>>> Further, if the attributes are "NULLABLE" - that is, there might not be a row in
>>>
>>> OBJECT_ATTRIBUTES for some attributes, you may have to outer join instead of just joining
>>> which in some cases can remove more optimal query plans from consideration.
>>>
>>> Writing queries might look pretty straightforward, but it's impossible to do in a
>>>
>>> performant fashion. For example, if we wanted to get everyone that was born in MARCH or
>>> has a LAST_NAME = 'SMITH', we could simply take the query from above and just wrap an
>>> inline view around that:
>>>
>>>
>>>
>>> ops$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 <http://objects.name>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.
>>>
>>>
>>> ------------------------------------------------------------------------
>>>
>>> _______________________________________________
>>> Serusers mailing list
>>> <mailto:Serusers at lists.iptel.org>Serusers at lists.iptel.org
>>> http://lists.iptel.org/mailman/listinfo/serusers
>>>
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Jiri Kuthan http://iptel.org/~jiri/
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