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From Francis De Brabandere <franci...@gmail.com>
Subject Re: All "prepared" now!
Date Fri, 03 Dec 2010 08:37:03 GMT
Busy night Rainer? Great to hear this is implemented :-) Too bad we
just cut a release :-s

On Fri, Dec 3, 2010 at 9:30 AM, Rainer Döbele <doebele@esteam.de> wrote:
> Hi Kenji,
>
> good news for you: it's all "prepared" now :-)
> Most of it was already there, but a few bits and pieces were missing.
> However you have to take the latest sources directly from our SVN repository.
>
> In DBDatabase you now have a property called "preparedStatementsEnabled" which you can
enable or disable.
> If enabled Empire-db will use prepared statements for all database operations on DBRecord.
>
> If you create your own commands using DBCommand you will have to explicitly declare the
parameters using DBCommand.addCmdParam() which will return a DBCommandParam (I have renamed
this inner class from DBCmdParameter!) except for set() operations.
>
> I have added an example to the empire-db-example-advanced (SampleAdvApp.java). The commandParamsSample()
method shows how to use command params.
> By additionally setting preparedStatementsEnabled to enabled, also all operations performed
by Empire-db itself will use prepared statements.
> You can easily see it in the log.
> And the good thing is, you can easily switch between prepared and non-prepared (non-prepared
statements are still better for debugging).
>
> Let me know, if you have problems or need any more help.
> Best regards,
>
> Rainer
>
>
> Kenji Nakamura wrote:
>> from: Kenji Nakamura [mailto:kenji_nakamura@diva-america.com]
>> to: empire-db-user@incubator.apache.org
>> re: Re: Prepared statement support?
>>
>> Hi Rainer,
>>
>> Yes, this is exactly what I was looking for.
>> Regarding statement pooling, it is a part of JDBC 3.0 spec and I think
>> it is a job of connection pool utility.
>> We use c3p0 and it has statement pooling capability. It is highly
>> configurable and has lots of features.
>>
>> http://www.mchange.com/projects/c3p0/index.html#configuring_statement_po
>> oling
>>
>> I really appreciate if you can include the bug fix of DBReader in the
>> next release as this is crucial feature to persuade DBAs and security
>> auditors.
>>
>> Thanks a lot!
>>
>> Kenji Nakamura
>>
>> On Dec 2, 2010, at 19:29, Rainer Döbele <doebele@esteam.de> wrote:
>>
>> > Hi everyone,
>> >
>> > thanks for your comment Matt.
>> >
>> > To my own surprise I have overlooked that there is already substantial
>> support for prepared statement generation in Empire-db now, but you have
>> to explicitly declare the parameters.
>> > Here is an example of how to generate a prepared statement phrase and
>> execute it with the corresponding parameters:
>> >
>> >    // Define the query
>> >    DBCommand cmd = db.createCommand();
>> >
>> >    // Create parameters
>> >    DBCmdParameter depIdParam  = cmd.addCmdParam(1);
>> >    DBCmdParameter genderParam = cmd.addCmdParam('F');
>> >
>> >    // create statement
>> >    cmd.select(EMP.getColumns());
>> >    cmd.where(EMP.DEPARTMENT_ID.is(depIdParam));
>> >    cmd.where(EMP.GENDER.is(genderParam));
>> >
>> >    // First execution
>> >    String sql = cmd.getSelect();
>> >    ResultSet r = db.executeQuery(sql, cmd.getCmdParams(), false,
>> conn);
>> >    // do something
>> >    r.close();
>> >
>> >    // Modify command parameters
>> >    depIdParam.setValue(2);
>> >    genderParam.setValue('M');
>> >
>> >    // Second execution
>> >    r = db.executeQuery(sql, cmd.getCmdParams(), false, conn);
>> >    // do something
>> >    r.close();
>> >
>> > This will result in the following SQL:
>> >
>> >    SELECT t2.EMPLOYEE_ID, t2...
>> >    FROM EMPLOYEES t2
>> >    WHERE t2.DEPARTMENT_ID=? AND t2.GENDER=?
>> >
>> > And set the parameter to 1 and 'F' for the first query and to 2 and
>> 'M' for the second.
>> >
>> > Unfortunately there is a bug in DBReader so that cmd params are not
>> properly set.
>> > This is the reason why I used db.executeQuery(..) instead of a
>> DBReader in the example above.
>> > I will fix this bug as soon as possible.
>> >
>> > Another thing we should do is to use the prepared statements for
>> DBRecord.read (which in turn uses DBRowSet.readRecord(...)).
>> >
>> > As far as the pooling of prepared statements is concerned, if it's not
>> done by the data source already it can also be done by subclassing the
>> DBDatabaseDriver and overriding executeQuery() and / or executeSQL() and
>> do it yourself. But it is not necessary for Empire-db to provide this.
>> >
>> > Kenji will this satisfy your needs?
>> >
>> > Regards,
>> > Rainer
>> >
>> >
>> >
>> > Matthew Bond wrote:
>> >> from: Matthew Bond [mailto:bond@bond-it.de]
>> >> to: empire-db-dev@incubator.apache.org; empire-db-
>> >> re: AW: Prepared statement support?
>> >>
>> >> Hi Rainer, Hi Kenji,
>> >>
>> >> Rainer's comments are true in a Web Application scenario where the
>> >> connection if got for a short time and then released again. Empire DB
>> >> can also be used in other scenarios, like a Fat Clients or Command
>> Line
>> >> Utility tools, where a connection will probably be held for the whole
>> >> duration of the application  lifetime and PooledStatements could
>> bring
>> >> more performance. So it really depends on what you application type
>> you
>> >> are programming.
>> >>
>> >> FYI: WebSphere too pools prepared statements (see page 2 of
>> http://www-
>> >>
>> 03.ibm.com/systems/resources/systems_i_advantages_perfmgmt_pdf_stmntcach
>> >> e.pdf  "WebSphere, however, will do the caching automatically. When
>> you
>> >> execute a query, WebSphere determines if the SQL text is already in
>> the
>> >> cache and if so, it will use that cached statement instead of
>> preparing
>> >> a new one." ). So if EmpireDB was extended to make more use of
>> Prepared
>> >> Statements it would be advantageous.
>> >>
>> >> However as Rainer describes,  the big benefit of using EmpireDB is
>> that
>> >> the selects are going to be way better than other ORM's as the
>> developer
>> >> hand crafts the "SQL" statement.
>> >>
>> >> The great thing is that it is Open Source so if you feel strongly
>> about
>> >> the use of PreparedStatements, you could submit a Patch adding this
>> >> functionality.
>> >>
>> >> Cheers
>> >> Matt
>> >>
>> >> -----Ursprüngliche Nachricht-----
>> >> Von: Rainer Döbele [mailto:doebele@esteam.de]
>> >> Gesendet: Donnerstag, 2. Dezember 2010 00:11
>> >> An: empire-db-user@incubator.apache.org; empire-db-
>> >> dev@incubator.apache.org
>> >> Betreff: re: Prepared statement support?
>> >>
>> >> Dear Kenji,
>> >>
>> >> I have reviewed our code and thought about this subject again.
>> >> As you mentioned there is both a performance and a security issue to
>> >> consider.
>> >> For the moment I would like to focus on the performance issue as
>> >> security can as well be established by other measures.
>> >>
>> >> It's pretty obvious to understand that creating a prepared statement
>> and
>> >> executing it multiple times with varying parameters is superior over
>> >> creating a normal statement each time. But as far as I understand it,
>> >> the advantage of a ps exists only as long as the statement lives, and
>> >> ends when you close it.
>> >>
>> >> The problem is, that a prepared statement is created for a particular
>> >> connection. In a web-application we usually use a connection pool and
>> >> the connection is fetched for a particular request. It is extremely
>> >> rare, that the same statement is executed multiple times within a
>> single
>> >> request - whereas it is very likely that the same statement needs to
>> be
>> >> executed by other users' requests. As those other users have
>> different
>> >> connections they cannot share the same prepared statement.
>> >>
>> >> Here is a thread discussing this issue:
>> >> http://www.velocityreviews.com/forums/t644638-jdbc-preparedstatement-
>> in-
>> >> a-multi-threaded-environment.html
>> >>
>> >> As Empire-db does not store or maintain a connection, it is not
>> sensible
>> >> for us to store the actual JDBC prepared statement object. But this
>> >> might not be necessary as it could be done on another level. Possibly
>> >> the solution lies just in another Apache Project: Apache Commons
>> DBCP.
>> >> http://commons.apache.org/dbcp/index.html
>> >>
>> >> From my understanding it should be possible to use a commons-dbcp
>> >> connection pool that will also pool prepared statements. The
>> connections
>> >> returned by the pool can be used with Empire db just like a normal
>> JDBC
>> >> connection.
>> >> Of course we still need to enforce and extend the generation of
>> prepared
>> >> statement phrases beyond the CUD operations.
>> >>
>> >> Still we must keep in mind, that probably for most real world
>> >> applications the performance benefit of prepared statements over
>> simple
>> >> statements is negligible, and it is our primary goal to maintain
>> >> simplicity and transparency.
>> >> It is IMO far more important to be able to create efficient
>> statements -
>> >> and avoid the problem of OR-Mappers that usually work with lots of
>> >> simple operations. After all, one clever statement with server side
>> db
>> >> logic will still execute a lot faster than 10 prepared statements
>> with
>> >> trailed Java logic.
>> >> (Still the gloal is to have it all of course)
>> >>
>> >> Any more suggestions or remarks on this topic?
>> >>
>> >> Regards
>> >> Rainer
>> >>
>> >>
>> >> Kenji Nakamura wrote:
>> >>> from: Kenji Nakamura [mailto:kenji_nakamura@diva-america.com]
>> >>> to: empire-db-user@incubator.apache.org
>> >>> re Re: Prepared statement support?
>> >>>
>> >>> Rainer,
>> >>>
>> >>> Thank you for your reply. My comment are inline.
>> >>>
>> >>> On Wed, Dec 1, 2010 at 2:14 AM, Rainer Döbele <doebele@esteam.de>
>> >>> wrote:
>> >>>> Hi Kenji,
>> >>>>
>> >>>> thanks for your interesting links about this subject.
>> >>>>
>> >>>> It is certainly true, that the performance of a prepared statements
>> >>> is better when you execute it multiple times with varying parameter
>> >>> values.
>> >>>> This is not always possible when varying statements with
>> conditional
>> >>> joins are created at runtime.
>> >>>> For a one-time statement using a prepared statement does not
>> execute
>> >>> faster than a normal statement.
>> >>>
>> >>> I understand the issue that the use of PreparedStatement seems to
>> have
>> >>> overhead and actually it may take longer if we measure it with a
>> >>> single execution from application developer's point of view, but the
>> >>> compiled result of the statement is kept added to Oracle's cache and
>> >>> it flushes the compiled results of the PreparedStatement invoked
>> from
>> >>> different applications as the cache is managed per SID in Oracle. So
>> >>> it has negative impact from the DBA's point of view.  It is not an
>> >>> issue as long as the DB is used as the data storage of a web
>> >>> application server and the performance of the app is only concern,
>> but
>> >>> the assumption is not true when the DB is also used in data
>> >>> processing.
>> >>>
>> >>>> The inclusion of parameter values in the SQL text when assembling
>> >>> statements is an advantage when it comes to logging (logging of
>> >>> parameterized statements is not sufficient to track errors) or for
>> the
>> >>> creation of SQL scripts that are saved and executed later.
>> >>>
>> >>> I see your point.
>> >>>
>> >>>>
>> >>>> Currently Empire-db uses prepared statements by default only for
>> >>> statements with BLOB and CLOB fields.
>> >>>>
>> >>>> However at least as far as update and insert statements are
>> >>>> concerned
>> >>> you can override the method useCmdParam() in DBCommandOracle, but
>> you
>> >>> need to subclass the DBDatabaseDriverOracle and override
>> createCommand
>> >>> first. If you return true in useCmdParam(), then Empire-DB will use
>> a
>> >>> prepared statement and supply this value as a prepared statement
>> >>> parameter.
>> >>>
>> >>> From the point of view of Oracle administrator, the primary interest
>> >>> is how to reduce the # of hard parse and increase the hit rate of
>> the
>> >>> cache, and using PreparedStatement only for CUD operation is not
>> >>> sufficient if the ratio of Select outweigh CUD operations. From
>> >>> security point of view, Select statement with parameters embedding
>> >>> user's input is as vulnerable as other DMLs, so the option to use
>> >>> PreparedStatement for CUD operation doesn't address those concerns,
>> >>> while it may be useful to improve the performance on iterative
>> >>> operations.
>> >>>
>> >>>>
>> >>>> Personally I have used Empire-DB in many projects and performance
>> or
>> >>> security have never been a problem. However, if you except to
>> execute
>> >>> 10.000 sql statements a minute then certainly this needs to be
>> >>> thoroughly checked.
>> >>>
>> >>> It is nice to know the framework has been proven in production
>> >>> environments. Our current performance test also doesn't show the
>> hard
>> >>> parse is the primary culprit of the performance bottleneck, so it is
>> >>> not an urgent problem, but I'd like prepare to answer the questions
>> >>> from our DB engineers.
>> >>>
>> >>>>
>> >>>> I have created a new Jira (EMPIREDB-91) issue for us to check, how
>> >>> and where we can increase and optimize the use of prepared
>> statements.
>> >>>
>> >>> Thank you for the reaction. I registered myself to the watch list.
>> Let
>> >>> me know if I can do something to make this forward.
>> >>>
>> >>> Lastly, I really thank you to share the framework in public. I have
>> >>> used Toplink, Hibernate, and iBatis, but I favor empire-db a lot
>> >>> because of the simplicity and type-safe coding. It is very
>> >>> straightforward to customize to fulfill our specific needs such as
>> the
>> >>> support of TableFunction in Oracle.
>> >>>
>> >>> Regards,
>> >>>
>> >>> Kenji
>> >>>
>> >>>>
>> >>>> Regards
>> >>>> Rainer
>> >>>>
>> >>>>
>> >>>> Kenji Nakamura wrote:
>> >>>>> from: Kenji Nakamura [mailto:kenji_nakamura@diva-america.com]
>> >>>>> to: empire-db-user@incubator.apache.org
>> >>>>> re: Prepared statement support?
>> >>>>>
>> >>>>> Hi,
>> >>>>>
>> >>>>> I got a question from one of our DB engineer about the use of
>> >>> prepared
>> >>>>> statements.
>> >>>>> According to him, or a thread in AskTom, it is always preferred
to
>> >>> use
>> >>>>> PreparedStatement instead of Statement whenever possible.
>> >>>>>
>> >>>
>> http://asktom.oracle.com/pls/asktom/f?p=100:11:7607696421577136::::P11
>> >>> _
>> >>> Q
>> >>>>> UESTION_ID:1993620575194
>> >>>>>
>> >>>>> As far as I looked at the code, PreparedStatement is not used
>> other
>> >>>>> than DBDatabaseDriver class and the method is not used from
other
>> >>>>> code.
>> >>>>>
>> >>>>> My understanding is that creation of PreparedStatement has certain
>> >>>>> overhead, but statement pooling introduced in JDBC 3.0 mitigates
>> >>>>> the impact especially from application server point of view.
>> >>>>> We use Oracle, and the DB engineer explained that the use of
>> >>> statement
>> >>>>> floods the library cache in SGA and reduce the hit rate of
>> >>>>> pre-compiled statements so it has negative impact on entire
db,
>> and
>> >>>>> using PreparedStatement simply reduces the cost of hard parse.
>> >>>>>
>> >>>>> Another aspect is about SQL injection prevention. I noticed
single
>> >>>>> quotes are escaped at DBDatabaseDriver#getValueString() method,
>> but
>> >>>>> the preferred way to prevent SQL injection is to use
>> >>> PreparedStatement
>> >>>>> according to OWASP website.
>> >>>>>
>> http://www.owasp.org/index.php/SQL_Injection_Prevention_Cheat_Sheet
>> >>>>>
>> >>>>> Would you tell me the design philosophy or reasons not to use
or
>> >>>>> provide the option to use prepared statement? Is it possible,
or
>> >>> have
>> >>>>> a plan to support PreparedStatement?
>> >>>>>
>> >>>>> Thanks,
>> >>>>>
>> >>>>> Kenji Nakamura
>> >>>>
>



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