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Re: Table open times and rowsize discontinuity

From: dean <deanbrown3d_at_yahoo.com>
Date: Mon, 13 Aug 2007 04:12:48 -0000
Message-ID: <1186978368.261448.3120@b79g2000hse.googlegroups.com>


On Aug 9, 11:28 am, DA Morgan <damor..._at_psoug.org> wrote:
> sybra..._at_hccnet.nl wrote:
> > On Wed, 08 Aug 2007 14:34:38 -0700, dean <deanbrow..._at_yahoo.com>
> > wrote:
>
> >> On Aug 8, 2:27 pm, DA Morgan <damor..._at_psoug.org> wrote:
> >>> dean wrote:
> >>>> Hello all,
> >>>> We have a table T with the following structure:
> >>>> Name Null? Type
> >>>> ----------------------------- -------- --------------------
> >>>> USER_I NOT NULL VARCHAR2(30)
> >>>> FORM_I NOT NULL VARCHAR2(100)
> >>>> CATEGORY_I NOT NULL VARCHAR2(100)
> >>>> KEY_I NOT NULL VARCHAR2(100)
> >>>> VALUE_X VARCHAR2(2000)
> >>>> By varying the VALUE_X field (varchar2(N)) from N=100 to N=2000,
> >>>> however, we can alter the time it takes to open this table either onto
> >>>> a grid or to scroll through all records. We are using Borland's
> >>>> TADOQuery here. Oracle is 9.2i or 10g, windows thick client over a
> >>>> LAN.
> >>>> All data was the same, however, since the longest actual VALUE_X field
> >>>> was onyl 27 characters.
> >>>> Times to open a TdbGrid on user_preference table:
> >>>> VALUE_X field: Time to open:
> >>>> varchar2(100): 10.44s
> >>>> varchar2(200): 10.75s
> >>>> varchar2(300): 10.91s
> >>>> varchar2(400): 10.93s
> >>>> varchar2(500): 11.21s
> >>>> varchar2(600): 11.15s
> >>>> varchar2(700): 28.44s <- steps up here
> >>>> varchar2(800): 26.84s
> >>>> varchar2(900): 26.59s
> >>>> varchar2(1000): 26.36s
> >>>> varchar2(1100): 26.78s
> >>>> varchar2(1200): 26.42s
> >>>> varchar2(1300): 26.78s
> >>>> varchar2(1400): 28.27s
> >>>> varchar2(1500): 28.96s
> >>>> varchar2(1600): 28.34s
> >>>> varchar2(1700): 27.64s
> >>>> varchar2(1800): 28.5s
> >>>> varchar2(1900): 28.13s
> >>>> varchar2(2000): 28.36s
> >>>> Why does this time step up at N = 700 characters? I have narrowed it
> >>>> down to the ADO component, since an alternative component (ODAC) does
> >>>> not report ANY differences, irrespective of the size of the field. SQL
> >>>> + also reports the same number of bytes transfered and times to open,
> >>>> irrespective of N.
> >>>> Similar effect was noted in an alternative table (one with around 30
> >>>> fields) at N = 600, so I am assuming the total rowsize is the property
> >>>> to consider.
> >>>> Thanks for any hint. We are considering removing such fields and using
> >>>> a lookup table in such cases, since the data is sparsely populated.
> >>>> Dean
> >>> Look at array size and cache size settings. My guess is that it is in
> >>> some manner related to ADO or the tool you are using (Delphi ?). It
> >>> isn't something experienced in the database. Something you can confirm
> >>> by running in SQL*Plus.
>
> >>> Anything you ever see in a tool, that you don't see in SQL*Plus, IS
> >>> the tool.
> >>> --
> >>> Daniel A. Morgan
> >>> University of Washington
> >>> damor..._at_x.washington.edu (replace x with u to respond)
> >>> Puget Sound Oracle Users Groupwww.psoug.org-Hide quoted text -
>
> >>> - Show quoted text -
> >> This is using a serverside cursor, so caching won't have any effect.
> >> For the array fetching, the only parameter I can find in the ADO
> >> documentation is to append FetchSize=N to the connection string that
> >> gets passed to Oracle, but I am not sure if ADO is over-riding this,
> >> since it has no effect.
>
> > As soon as the number of records fetched times the record size exceeds
> > sqlnet's SDU and/or your network's MTU, you will potentially see
> > remarkable slowdowns.
> > Just increasing the array fetch size to the ceiling doesn't help.
> > Many years ago I conducted an investigation for an online banking
> > system.
> > It appeared that as soon as I increased sql*plus array size to
> > anything above 10, performance collapsed. This was the net result of
> > exceeding the SDU and the MTU.
>
> Interesting. I normally set SDU on Oracle systems to 32K, as recommended
> in the HA docs, rather than using the default 2K. Perhaps that is why I
> haven't seen it.
> --
> Daniel A. Morgan
> University of Washington
> damor..._at_x.washington.edu (replace x with u to respond)
> Puget Sound Oracle Users Groupwww.psoug.org- Hide quoted text -
>
> - Show quoted text -

I'd like to investigate this - are these settings on the Oracle server, or some part of the TCI/IP setup? Received on Sun Aug 12 2007 - 23:12:48 CDT

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