On May 28, 2007, at 1:50 PM, Aristedes Maniatis wrote:
On 28/05/2007, at 4:49 PM, Andrus Adamchik wrote:
No. "resolvesFirstPage" really a shorthand for "is it possible to
reliably resolve objects on the first page using the existing
algorithm".
OK. I guess I would have named it isFirstPageResolvable() or
canResolveFirstPage(). But from your description it appears that it
isn't specific to the first page and that either it is resolvable
for any page, or not. So does it mean canResolveData()?
Actually no. This is specific to the first page that most of the time
can be resolved from the "select *" query result set, while the
second and following pages are resolved using separate queries that
select a group of id's.
Just to confirm, is this a JDBC test or a test using DB client
tools (on Derby this may be the same thing, still worth doing a
JDBC run with your own code, as there can be unrelated bottlenecks
in the tools). E.g. create two PreparedStatements, one with
"select *", another with "select id", and only read "id" column in
both resultsets. See how much faster the second case is.
OK. I just tried it a different way and the results are the same.
In this case I used the Derby ij tool to make a JDBC connection to
a Derby server on localhost. That server has real data from one of
our clients with 120,000 students.
select * from student; -> 53 seconds
select id from student; -> 4 seconds
I performed several runs to try and exclude cache warming and the
variance was less than 10%. The output was redirected to a file on
disk. There are around 30 columns in the student table with a range
of data types. The output file on disk with all the fields was
120Mb when finished.
Could you also exclude "ij" from the picture? It can add the overhead
of the terminal I/O, and the overhead of actually reading those extra
29 columns - something Cayenne paginated query wouldn't do. What I
think of as a *clean test* in this situation is a small Java program
that opens a Connection, creates a PreparedStatement, and reads a
ResultSet, discarding the data. In case of "select *" it would still
only read the "id" column.
Thanks
Andrus
