3 Dec
2007
3 Dec
'07
9:37 p.m.
I disagree entirely that it's strictly based on
migration.
Let's look at the simple act of adding information to the system:
With a flat subscriber table with all the fields I desire, adding
information to the system is 1 insert.
Let's say that my subscriber table looks like this (because in the dev
ser 0.9.6 box, it does):
+-------------------+--------------+------+-----+---------------------+-------+
| Field | Type | Null | Key | Default |
Extra |
+-------------------+--------------+------+-----+---------------------+-------+
| phplib_id | varchar(32) | NO | UNI |
| |
| username | varchar(64) | NO | PRI |
| |
| domain | varchar(128) | NO | PRI |
| |
| password | varchar(25) | NO | |
| |
| first_name | varchar(25) | NO | |
| |
| last_name | varchar(45) | NO | |
| |
| phone | varchar(15) | NO | |
| |
| email_address | varchar(50) | NO | |
| |
| datetime_created | datetime | NO | | 0000-00-00 00:00:00
| |
| datetime_modified | timestamp | NO | | CURRENT_TIMESTAMP
| |
| confirmation | varchar(64) | NO | |
| |
| flag | char(1) | NO | | o
| |
| sendnotification | varchar(50) | NO | |
| |
| greeting | varchar(50) | NO | |
| |
| ha1 | varchar(128) | NO | |
| |
| ha1b | varchar(128) | NO | |
| |
| allow_find | char(1) | NO | | 0
| |
| timezone | varchar(128) | YES | | NULL
| |
| rpid | varchar(128) | YES | | NULL
| |
| domn | int(10) | YES | | NULL
| |
| uuid | varchar(64) | YES | | NULL
| |
| signup_ip | varchar(15) | NO | |
| |
+-------------------+--------------+------+-----+---------------------+-------+
Now... ignoring the fact that we have 1 possibly 2 unused fields in that
table, let's assume we have to add a user in the new schema.
let's be first just a bit more accurate:
- uuid, username,password,domain name, ha's, and their equivalents are
like before in the table, which is now called credentials (about 7)
- so we are speaking about the application stuff, which may be very
different for different uses: callid, signup_up, timezone, email
address, confirmation string, etc. etc. (about 15, how many depending
on the actual deployment -- I'm wondering who is for example using
"sendnotification")
That's 22 inserts right there (one for each
attribute, especially since
we can't have defaults).
I would guess about ten as opposed to 22.
Nevertheless, as long as they are inserted by machines as opposed to
humans, I'm less worried about that.
Searching through data? Let's say I want to know
the
first_name,last_name,username,domain,confirmation, and the
datetime_modified of a user. Simple enough. That's 1 query. If any of
those data points were null or their default, grabbing that is still
easy as can be.
Now... in the new schema, that's a join (which IS less efficient than a
query,
It is not necessarily join -- it may be a double query, with the first
query being trivial (delivering UID) and the second actually too
(querying attributed by UID). Many applications have UID stored about
lifetime of their session (a subscriber logs in, his UID is stored)
and effectively carry out only the latter query.
I'm afraid, though I can't quote exact
meaningful metrics on how
much).
Well, without that, this discussion is a bit missing grounds.
I mean we can't really speak about performance concerns unless
we have the numbers for it.
If any of those data points are not SET (assuming we
were going
to minimise our impact by NOT doing a full 22-insert creation for each
user), it causes yet another series of headaches. When you want to
reference data in other relations, it becomes even MORE of a hassle. The
queries themselves become these unwieldy beasts that increase the chance
of an error in syntax or logic.
One of the simplest queries we have is with our admin interface to query
who's logged in in such a way that the data will be used in the web
interface:
select username, first_name, last_name, signup_ip from subscriber where
username=ANY (select username from location);
Simple. Succinct. Clear.We grab the fields we need and can format them.
One short line.
I would add in your languagne "non-relational" too. Squizing everything
you can in a single table does not have much of relation in it, does it?
Now I'll leave the new schema version as an
exercise for the reader, as
I don't recall the syntax right off (which is the first clue as to its
added complexity). It's lengthy and utterly non-relational -- which is
why we simply don't USE it for these sorts of things.
I understand that formulating a query may be more complex here, and
that's for sure a good point.
This is not just a migration headache. This is a schema
problem. Now, I
know you love your schema, and you're allowed, and I fully understand
that it's flexible and good for the SER service. But for integration
with any sort of system beyond the most basic, it's a right pain in the
ass. You can tout its joys and wonders all you'd like, but we're
developing with it, and I can assure you, it's not as easy and as
straightforward as you like to believe.
Maybe it depends on the type of apps you develop. We have had very
dynamic apps too (say a la phpmyadmin), and the pain of changing scheme
was unbearable.
I'm not saying there's anything wrong with the
schema overall. There
have been some great forward leaps in this one, such as the riddance of
the incredibly tiresome domain column in every table (that was sometimes
checked and sometimes not). But it DOES make for additional complexity
when building a system around it.
Point taken, that's for sure agreeable.
Again, if you think that's a way too big obstacle, doing a patch which allows
to read AVPs from credentials table should be easy and should not cause
conflicts with rest of codebase. It could be even done in a way that works
over both types of structures. (Despite a certain mess risk.)
-jiri
N.
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Jiri Kuthan http://iptel.org/~jiri/