[icinga-devel] Draft - making NDOutils/Idoutils obsolete

Axel Liljencrantz axel.liljencrantz at freecode.no
Tue May 19 09:33:26 CEST 2009


On Mon, 2009-05-18 at 17:59 +0200, mareadmin wrote:

...
> i think, there should be no non-standard-queries at all to keep
> compatibility with as much rdbms as possible ... if this
> is possible, i don't know. 

Yes, it would be very desirable. But it is very close to impossible in
practice. There are an amazing number of incompatibility issues between
different databases:

* Oracle treats empty strings as nulls, other databases treat null and
an empty string as two different concepts.

* Databases have extremely different performance characteristics, e.g.
you need subselects to get any work done in Oracle, but they are
amazingly slow in MySQL.

* Different databases use different rules for case sensitivity, e.g.
oracle implicitly converts everything to upper case, mysql is case
sensitive on table names but not on column names.

* Different databases use different quoting rules, both for string
literals and for quoted field names.

* Most databases are typed, but some, like sqlite, are more or less
untyped, which makes them behave subtly different in some situations
where casting is involved.

* Bulk inserts (insert many lines into a table with a single query) are
not covered by standards, but is a critical feature if you want to
insert large chunks of data in semi-reasonable time.

* Inserting a column and getting back the row id of the column inserted
is often useful, and also handled differently in many databases.

I could go on until tomorrow afternoon. Databases are a bit of a
hopeless mess. Most of these issues can be somewhat papered over with a
database abstraction layer, but at a cost in expressiveness and speed.
I've seen high-tech abstraction APIs like SQLAlchemy used in large,
complex projects. SQLAlchemy allows you to write a database query as
plain old Python code, and it then rewrites it into a hopeless mess of
buggy, slow SQL in the dialect of your choice. In my opinion, the best
trade off is a moderatly thin abstraction library and trying to write
most queries in a database independent manner, but making special
optimized versions of a few, special queries. I think SUN got it
reasonably right with JDBC, though I'm sure others disagree.


Axel

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