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

1. DAO files might become very long.
2. If you decide to return the business entity associated with the DAO as a returned object, you won't know as a caller which fields to expect to be populated, which lead to 3:
3. An inflation of business entities to represent partial populated business entity or inflation of mappers inflation (this will be required for SP as well).
4. SQL code inside of Java:
   
1. Beside of the fact that a multi-line concatenated string that cannot be easily copied and run with psql, it means that we should compile the code in order to test the change (vs building with DEV_REBUILD=0 which only package the SQL file).
2. No syntax highlighting when performing code review. i.e. I don't think reviewing a patch such as https://gerrit.ovirt.org/#/c/66729/10/packaging/dbscripts/network_sp.sql would be more clear inside a java file.
3. The user permissions management is implemented on DB level. That means that SQL will be more complex (more concatenated java lines).
5. Stored procedure are cached by project's code. See SimpleJdbcCallsHandler.getCall(), while the NamedParameterJdbcTemplate are cached by spring's code which seems less optimal (sync all calls using synchronized vs using ConcurrentHashMap as in SP cache).
6. With the NamedParametersJdbcTemplate there is no use of the DbEngineDialect. What's the impact of it ?

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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