[ovirt-devel] Writing SQL queries in DAO code

[Yevgeny Zaspitsky]

Hi All,

Recently I had a task of performance improvement in one of our network
related flows and had some hard time following our DAL code and one of the
outcomes of the task was defining a couple of new quite simple, but neat
queries.
When I came to coding those new queries I remembered how hard was following
the existing DAL code, I decided to make my own new methods clearer. So I
created [1] and [2] patches.

Everything is quite standard there beside the fact that they do not use any
stored procedure, but use SQL directly, IMHO by that they save time that I
spent in trying to follow what a DAO method does. Looking into the method
code you get the understanding of what this method is all about:

   - no looking for a stored procedure name that is buried in the DAO class
   hierarchy
   - no looking for the SP definition

So I'd like to propose moving towards this approach in general in all cases
when nothing beyond a simple SQL is needed (no stored procedure programming
language is needed).
>From my experience with the performance improvement task it looks like
people avoid adding new queries for a specific need of a flow, instead they
use the existing general ones (e.g. dao.getAllForX()) and do the actual
join in the bll code.
IMHO the proposed approach would simplify adding new specific queries and
by that would prevent a decent part of performance issues in the future.

I do not propose changing all existing SP's to inline queries in a once,
but to allow adding new queries this way. Also we might consider converting
relatively simple SP's to inline SQL statements later in a graduate way.

[1] - https://gerrit.ovirt.org/#/c/74456
[2] - https://gerrit.ovirt.org/#/c/74458

Regards,
Yevgeny
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