Re: [cx-oracle-users] AW: cx-oracle-users digest, Vol 1 #99 - 8 msgs
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Re: [cx-oracle-users] AW: cx-oracle-users digest, Vol 1 #99 - 8 msgs
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From: Chris D. <cdu...@ya...> - 2005-05-12 09:32:14
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Danny,
Thanks for the idea, I'll give it a look.
Chris
--- "D.R. Boxhoorn" <da...@as...> wrote:
>
> Hoi Chris,
>
> Have you considered the following decorate/undecorate pattern?
>
> SQL: SELECT strcolumn || 'x' FROM ...
>
> python: strcolumn = row[0][:-1]
>
> As far as I can tell this will give about as much overhead as an if statement.
> However, only benchmarking your application will tell you what works best.
>
> Danny
>
>
> On Thu, May 12, 2005 at 01:22:56AM -0700, Chris Dunscombe wrote:
> > Henning,
> >
> > I know what you mean, but the issue is that this "if test" has to go in some sort of function
> and
> > be called for each col returned in each row and it's the function call overhead that's really
> the
> > issue. I'd like to use the following:
> >
> > append = rowsOutput.append
> > for row in data: # where data is the resultset from a query
> > rowsGroup = rowsGroup + 1
> > append("%s%s%s%s" %(row[0], colSep, row[1], colSep)) # In reality many more columns
> > append(recSep)
> > if rowsGroup > :
> > outFile.write(''.join(rowsOutput))
> > rowsGroup = 0
> > rowsOutput = []
> > outFile.write(''.join(rowsOutput))
> >
> > Now if I need to do the test on None then I believe I need to call a function or have the if
> test
> > inline in a loop and with many columns this is quite an overhead. In my test case on a 13
> column
> > table returning 200K rows:
> >
> > Doing the if test approx 20 CPU secs in Python
> > No if test approx 16 CPU secs secs in Python
> >
> > A 20% reduction. I know the numbers here are small but given the app will be running against
> many
> > tables concurrently and extracting millions of rows the potential saving is significant.
> >
> > Thanks for taking the time to respond.
> >
> > Cheers,
> >
> > Chris
> >
> > --- Henning von Bargen <H.v...@t-...> wrote:
> > > Chris,
> > >
> > > why do you think the simple statement "if x is None: x=''" means an
> > > overhead?
> > > It means about 0.000(insert zeroes here)1 percent performance overhead,
> > > because transferring/outputting the data is what takes most of time.
> > >
> > > And - with Python - it should not mean too much typing overhead.
> > > You could easily write a function to do this automatically for each
> > > record.
> > >
> > > HTH
> > > Henning
> > >
> > >
> > > > -----Urspr?ngliche Nachricht-----
> > > > From: Chris Dunscombe <cdu...@ya...>
> > > > To: cx-oracle-list <cx-...@li...>
> > > > Subject: [cx-oracle-users] Nulls returned as None and not as
> > > > as "empty or zero lenght string"
> > > > Reply-To: cx-...@li...
> > > >
> > > > All,
> > > >
> > > > Is there anyway that Null values returned from a query can be
> > > > an "empty or zero length string"
> > > > instead of None?
> > > >
> > > > This may seem a strange request as it's easy to use type to
> > > > test if a null has been returned as
> > > > None. However I've a performance critical app where I need to
> > > > output "nothing" (zero length /
> > > > empty string) if the value is null. Hence at present I have
> > > > to perform this "type test" on ALL
> > > > columns that don't have a "Not Null" constraint in the
> > > > database which is quite an overhead when in
> > > > some cases I need to do it millions and sometimes billions of times.
> > > >
> > > > Thanks,
> > > >
> > > > Chris Dunscombe
> > > >
> > >
> > >
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