[ovirt-devel] Writing SQL queries in DAO code

Mon Mar 27 09:26:17 UTC 2017

> I don't think that looking in SQL in Java code is clear than looking in
a SP code

Looking in SQL isn't the problem I'm trying to solve, but finding that.

> 1) You will pass more data on the wire instead of calling a SP with
parameters

Passing the SQL string shouldn't be a problem unless that is very long one
(several K) and then we probably do something wrong.

> 2) Your data that is passed on the wire is exposed to attacks since you
will have to implement DB security in the engine level (for example hidden
columns).

IIUC currently querying tables/views with hidden columns is implemented in
a SP that consist of at least 2 SQL's, so those aren't good candidates for
my proposal and will stay as is.
BTW how other projects resolve the security problem? AFAIK usually hidden
columns are hidden by defining a proper view that do not include those.

> 3) Changes in the SQL code done in patches may be more complicated to
track

Most of SQL code changes involve changes in a DAO too, so this shouldn't be
an issue.

> 4) SQL Injection

Again, how other projects resolve the security problem? Internet is full of
articles/blogs of why stored procedures should be avoided ("avoid stored
procedures" Google query returned ~6.6M results), so I guess there are some
other approaches for the security issue if that exists.

> 5) I think that SP performs better than SQL inside Java

Do we have a measurement of how much better?
One of my intentions for this proposal is that people evidently avoid
creating neat SQL queries and re-use the existing ones, which has much
bigger performance impact. I guess that the biggest limit here is how
complicated that procedure is in the engine code.

On Mon, Mar 27, 2017 at 11:09 AM, Eli Mesika <emesika at redhat.com> wrote:

>
>
> On Mon, Mar 27, 2017 at 1:56 AM, Moti Asayag <masayag at redhat.com> wrote:
>
>>
>>
>> On Sun, Mar 26, 2017 at 5:12 PM, Yevgeny Zaspitsky <yzaspits at redhat.com>
>> wrote:
>>
>>> 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
>>>
>>>
>> There are additional pros and cons for the suggestion to consider:
>>
>> Pros:
>>
>>    1. No need to run engine-setup after changing DB related code (in
>>    case of SQL inside Java).
>>
>> Cons:
>>
>>    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/ne
>>       twork_sp.sql
>>       <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 besides 5 and 6, the rest is a matter of style. I'd like to hear more
>> opinions from other members.
>>
>
> I agree with all you wrote Moti
> I don't think that looking in SQL in Java code is clear than looking in a
> SP code
> Additionally
> 1) You will pass more data on the wire instead of calling a SP with
> parameters
> 2) Your data that is passed on the wire is exposed to attacks since you
> will have to implement DB security in the engine level (for example hidden
> columns)
> 3) Changes in the SQL code done in patches may be more complicated to
> track
> 4) SQL Injection
> 5) I think that SP performs better than SQL inside Java
>
> I see no real reason to replace the SPs with SQL code , SP is just a
> container for SQL code
>
>
>
>>
>> Regards,
>> Moti
>>
>> 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
>>>
>>> _______________________________________________
>>> Devel mailing list
>>> Devel at ovirt.org
>>> http://lists.ovirt.org/mailman/listinfo/devel
>>>
>>
>>
>>
>> --
>> Regards,
>> Moti
>>
>> _______________________________________________
>> Devel mailing list
>> Devel at ovirt.org
>> http://lists.ovirt.org/mailman/listinfo/devel
>>
>
>
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