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From: Michael Peppler <mpeppler at peppler dot org>
Subject: Re: DBD::Sybase and packet sizes
Date: Mar 16 2004 1:57PM
On Mon, 2004-03-15 at 18:41, Matthew O. Persico wrote:
> On Mon, 15 Mar 2004 17:58:42 -0800, Michael Peppler wrote:
> >On Mon, 2004-03-15 at 17:28, Matthew O. Persico wrote:
> >>We have modified our servers to set the maximum packet size to
> >>4096, up from 512. We did this because the main app (commercial
> >>software) we use works MUCH better with it. This app requires us
> >>to set a flag on its command line (the size to use, in this case
> >>4096) to pass down to Sybase in order to get the better
> >>performance. In addition, we wish to pass down 4096 to direct
> >>DBD::Sybase connections and to some old 'C' code using DBlib
> >>Question 1: Now, according to what I've read, if you pass a CTlib
> >>app a value for packetsize that is too high, the connection will
> >>successfully negotiate a good value. Since DBD::Sybase uses CTlib
> >>under the covers, I suspect that I can throw 4096 into the DBI
> >>connection string with no ill effects, even if the max allowed by
> >>the server is less. Ditto for a straight CTlib app. True or false?
> >Not quite - at least not during my quick tests involving OpenClient
> >Both DBlib and CTlib logins fail if you set the packet size larger
> >than the max allowed.
> >The error message is:
> >4024 10 2 0 luthien The packet size (4096) specified at login time
> >is illegal. Legal values are between 512 and 2048.
> >and is the same for both Client Library and DB-Library apps.
> Hmm. Look at this:
> Either I am interpreting it incorrectly or it has changed in 12.5.1,
> in which case, you have to ask Sybase, "Where are the new CT docs for
Interesting. I think I'll have to dig into this a little deeper - maybe
I'm not setting the property correctly in the Sybase::CTlib/DBD::Sybase
> >DBD::Sybase, Sybase::CTlib and Sybase::DBlib could be recoded to
> >check for the 4024 error message at connect time, and retry lower
> >packet sizes as needed, but at the moment the connect fails if you
> >specify a packet size that is larger than the max supported.
> Perhaps a patch will be in the mail...
> >>Question 3: Is there a way in Sybase::DBlib (and raw DBlib for
> >>that matter) to query the server for the allowed max packet size?
> >>I think that dbgetpacket gives the size of the current connection,
> >>not the max allowed.
> >sp_configure 'max network packet size'
> >will give you the value you're looking for.
> So, I could connect default size, do("sp_configure 'max network
> packet size'"), reconnect. Sounds like a strategy to me.
> One more question. This commercial app has a PC client and a UNIX
> client. The UNIX client runs on the same physical box as the Sybase
> server (no, I did not design the network topology) to that we can
> specify the full 4096 to the UNIX client. But, we were told that the
> PC client only works at a max of 1536 because the PC client is not on
> the same phisical box and is limited by the network. Does this sound
The network might use smaller packets at the physical layer, but the
larger packets as Sybase sees them would still be very useful.
Michael Peppler Data Migrations, Inc.
Sybase T-SQL/OpenClient/OpenServer/C/Perl developer available for short or
long term contract positions - http://www.peppler.org/resume.html