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:[EMAIL PROTECTED]
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);
