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From Kristian Waagan <Kristian.Waa...@Sun.COM>
Subject Re: Derby JDBC Embedded Driver, Prepared Statements, and Indexes
Date Wed, 08 Mar 2006 21:51:40 GMT
Michael Segel wrote:

>I have to agree with Mike that there is something missing.
>
>First, how often are you preparing the statement?
>You should only be preparing it once and within the look, set the variables
>and then execute it your 1000 times.
>  
>

Hi Michael,

The way I interpret Thomas' mail, I think the paragraph above can be 
misunderstood. The variables, assuming these refer to the question marks 
in the SQL prepared statement, must also be set 1000 times. Thomas, if 
I'm wrong, please correct me!
In code (parts from Thomas' mail):

-- Example Java Code - NB! No exception handling in the example code!!!!
PreparedStatement pStmt = connection.prepareStatement("SELECT * from MyTable
WHERE fk = ? AND date_millis <= ? ORDER BY date_millis DESC");
ResultSet rs = null;
// Execute the prepared statement 1000 times.
for (int i=0; i < 1000; i++) {
	pStmt.setInt(1, getSomeNumber());
	pStmt.setLong(2, getSomeBigNumber());
	rs = pStmt.executeQuery();
	while (rs.next()) {
		// Do something with the result.
	}
	rs.close();
}
pStmt.close();


It is not quite clear to me from the mail if the prepared statement is 
called in such a tight loop as above. If not, it is still important to 
only prepare the statement once as Michael says, and only set the 
variables and call one of the execute methods for each time. Also, 
closing database resources when they are not going to be used any more 
is recommended to free up resources in the database.



--
Kristian

>You may see 2 seconds on the first iteration, but after that, it should be
>very fast.
>
>>From your code example, it looks like you're calling the query once and then
>running through the result set. Is that what you're timing?
>
>Sorry, perhaps I'm running slow today... (late night drinking with some of
>my wife's co-workers) but I'm not sure I'm following you.
>
>Is the goal to prepare a statement, then time the amount of time required to
>run through the query's result set?
>
>Or are you preparing a statement, to be used 1000 times and you're timing
>the execution of the prepared statement?
>
>That's the first issue. 
>
>The second issue, that Mike points out is that you may be comparing apples
>to oranges depending on how you reset your test environment between
>querries.
>
>So can we start again, with some more background detail?
>
>Danke!
>
>-Mikey
>
>
>  
>
>>-----Original Message-----
>>From: Mike Matrigali [mailto:mikem_app@sbcglobal.net]
>>Sent: Wednesday, March 08, 2006 1:13 PM
>>To: Derby Discussion
>>Subject: Re: Derby JDBC Embedded Driver, Prepared Statements, and Indexes
>>
>>I believe that no index is actually created on MyTable, only on
>>AnotherTable.  From the one query below it seems like you want
>>an index on (fk asc, date_millis desc).  But if you run other
>>queries then other indexs may make more sense.
>>
>>I am not sure exactly what is going on with your performance
>>measurements, it has the feel of comparing compile time vs execute
>>time and/or cached table data vs uncached table data.
>>
>>Could you explain exactly how you get your performance measurement, it
>>is clear below with the SQuirreL example but not with the java code.  The
>>results have the feel of comparing compile time vs. execution time of
>>a prepared statement and/or cached db vs. not cached db.  Note that once
>>a query is compiled it is cached,
>>so you may be saving compile in squirrel without knowing it if you are
>>leaving the db booted and the query was sometime compiled what squirrel.
>>
>>Thomas J. Taylor wrote:
>>    
>>
>>>Hi everyone,
>>>
>>>I have a table with 400,000+ records in it and a foreign key (and index)
>>>      
>>>
>>to
>>    
>>
>>>a BIGINT value in another table. Through JDBC/Embedded Driver it takes
>>>      
>>>
>>about
>>    
>>
>>>2 seconds to retrieve a single value from the table using a simple
>>>      
>>>
>>SELECT
>>    
>>
>>>query as a PreparedStatement. I use a PreparedStatement as I call the
>>>      
>>>
>>query
>>    
>>
>>>up to 1,000 times, replacing the values of 'fk' and 'date_millis' during
>>>each call.
>>>
>>>Through SQurrieL, with the same database and Derby Embedded driver,
>>>executing the query takes 15ms. If I drop the foreign key and index, it
>>>takes 8862ms - both times using Derby runtime statistics.
>>>
>>>Does anybody know of a reason that the PreparedStatement is always
>>>      
>>>
>>taking
>>    
>>
>>>~2sec to complete, while SQuirreL takes 15ms to complete a similar
>>>      
>>>
>>query?
>>    
>>
>>>Any help is appreciated.
>>>
>>>Thomas
>>>
>>>
>>>-- Example Table
>>>CREATE TABLE MyTable (
>>>   dbid BIGINT IDENTITY GENERATED BY DEFAULT,
>>>   col1 VARCHAR(255),
>>>   col2 VARCHAR(255),
>>>   date_millis BIGINT NOT NULL,
>>>   fk BIGINT,
>>>   FOREIGN KEY fk REFERENCES AnotherTable (dbid)
>>>);
>>>
>>>-- Example Java Code
>>>PreparedStatement pStmt = connection.prepareStatement("SELECT * from
>>>      
>>>
>>MyTable
>>    
>>
>>>WHERE fk = ? AND date_millis <= ? ORDER BY date_millis DESC");
>>>..
>>>ResultSet rs = pStmt.executeQuery();
>>>
>>>-- Example SQuirreL SQL Code for stats
>>>CALL SYSCS_UTIL.SYSCS_SET_RUNTIMESTATISTICS(1);
>>>CALL SYSCS_UTIL.SYSCS_SET_STATISTICS_TIMING(1);
>>>
>>>SELECT * from MyTable WHERE fk = 413689 AND date_millis <=
>>>      
>>>
>>9999999999999999
>>    
>>
>>>ORDER BY date_millis DESC;
>>>
>>>VALUES SYSCS_UTIL.SYSCS_GET_RUNTIMESTATISTICS();
>>>CALL SYSCS_UTIL.SYSCS_SET_RUNTIMESTATISTICS(0);
>>>CALL SYSCS_UTIL.SYSCS_SET_STATISTICS_TIMING(0);
>>>
>>>
>>>
>>>
>>>      
>>>
>
>
>
>  
>


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