RE: Asynchronous vs Synchronous

Maybe he means the type of server? A dedicated one serves synchronously its client request, and a multithreader (MTS) dispatcher works async beetween more clients. Seems unprobably, but I have no other idea.

oli.

On Wed, 19 Jul 2000, Christine Turner wrote:
> Hello All,
>
> This is the response I received from my developer that he received from Crystal. Anyone have any comments?????
>
> Thanks In Advance,
> Cheers!
> Christine Turner
> Database Administrator
> IPS-Sendero
> Scottsdale, Arizona
> Phone: (800) 321-6899 ext. 3286
> Fax: (480) 946-8224
> E-mail: christine.turner_at_ips-sendero.com
>
>
>
> -----Original Message-----
> From: David Denison [SMTP:david.denison_at_ips-sendero.com]
> Sent: Tuesday, July 18, 2000 3:47 PM
> To: Christine Turner
> Subject: Fw: CTL:20000717-10296 Automated Response:
>
> Here is that Crystal response concerning synchronous vs. asynchronous
> database connections.
>
> ----- Original Message -----
> To: <david.denison_at_ips-sendero.com>
> Sent: Tuesday, July 18, 2000 1:32 PM
>
>
> > This EMail was sent: 7/18/00 1:32:20 PM (Pacific Standard Time)
> >
> > *** This incident has been closed. To reopen, simply reply to this email
> > with the additional information. Do not use this Control Number for a
> > different question as it will go to the wrong support group ***
> >
> > --------------------------------------------------------------------------
> > ------------------------------------
> >
> > Response To: David Denison
> >
> > Hi David,
> >
> > Thank you for using Answer by email.
> >
> > Unfortunately what you're trying to do will cause a gpf, and let me
> > explain why.
> >
> > If we submit a query to your database (in this case Oracle), we send off a
> > SQL statement (i.e select * from table). Oracle processes that statement
> > and generates a dataset and passes that back to Crystal Reports to format
> > and display.
> >
> > If we cancel the job or close that preview window before that data comes
> > back there's no way to tell Oracle that we've cancelled that job and it's
> > going to continue sending data to memory that Crystal Reports has already
> > released back to Windows and it will crash. This bi-directional
> > communication would require an asynchronous database driver on BOTH the
> > Crystal Reports side of the connection and the Oracle side of the
> > connection. Unfortunately, to my knowledge, Oracle doesn't support an
> > asynchronous connection, and Crystal Reports only supports asynchronous
> > connections with a limited number of our database drivers.
> >
> > I've included a Crystal Reports knowledge base article that describes
> > which of our database drivers are asynchronous:
> > c2006041
> >
> > I've also pasted this knowledge base article below:
> >
> > Asynchronous Database Connection Support for Seagate Software
> >
> > Product: Crystal Reports Professional Edition Version: 8.0.0.371
> > Applies to: Reported version and higher
> > Database: Microsoft SQL Server Platform: Windows 95 Date Verified:
> > February 16, 2000
> >
> > Problem:
> > Q: What happens when a user sends off a query in Crystal Reports (CR) or
> > in the Info Report Designer in Seagate Info (SI) and then needs to cancel
> > that query? How does the processing stop or does it even stop?
> >
> > Q: What is the difference between Synchronous and Asynchronous database
> > connections?
> >
> > Q: Does Seagate Software support Asynchronous database connection?
> >
> >
> > Solution:
> > There are two possible database connection methods with any type of
> > database. They are:
> > . Synchronous Database Connection
> > . Asynchronous Database Connection
> >
> > An asynchronous database connection refers to the ability for a client
> > application to be able to issue any number of commands to a database
> > server at any given point during the database connection, without waiting
> > for the database server to complete the processing of current tasks.
> >
> > A primary application of asynchronous database connections, within the
> > Crystal Reports (CR) Designer, is the ability to terminate a running query
> > at any point in time.
> >
> >
> > Definitions:
> > =================
> > Synchronous Database Connection:
> >
> > Synchronous connection to a database means that once a SQL query is passed
> > to the database server, the calling application (Crystal Reports in this
> > case) waits until it receives a "Finished" message from the database
> > server. The "Finished" message is connected to the first packet of the
> > result set being sent back.
> >
> > In Crystal Reports, if the cancel button is clicked while a synchronous
> > connection is underway, the Report Designer will look as though it has
> > canceled the query request. However, the request on the database server
> > will continue to process until completion. Once the first packet comes
> > back saying "Finished", no more of the query result set will be passed
> > back.
> >
> > NOTE: Actually, when executing the query synchronously, Crystal Reports
> > doesn't get the chance to cancel since the database client won't return
> > control until the database is finished.
> >
> >
> > Asynchronous Database Connection:
> >
> > Asynchronous connection to a database means that multiple sets of commands
> > can be passed to the database server and processed at once. (For example,
> > there is no need to wait for the query to return before sending another
> > command to the database server).
> >
> > Instead of waiting for a "Finished" message to be sent back from the
> > database server, the calling application (Crystal Reports in this case)
> > sends a query status message to the database server at set times asking
> > "Are you done yet?" When the database server says "Yes", the result
> > packets start coming back. However, if a cancel button is clicked on the
> > client computer side, instead of sending a question message to the
> > database server, the client application has the ability to send a "Cancel
> > query" message to the database server. In the Crystal Reports scenario,
> > if the cancel button is clicked, instead of asking the database server if
> > it has completed its query, Crystal Reports sends a "cancel" message to
> > the database server. The query never has to complete.
> >
> >
> >
> > Database Drivers that support Asynchronous Connections:
> > =====================================================
> > The following CR database drivers include support for asynchronous
> > database connections:
> >
> > . Microsoft SQL Server Direct (P2ssql.dll) - 8.0.0.1 and higher
> > . Sybase Direct (P2ssyb10.dll) - 8.0.0.0 and
> > higher
> > . IBM DB2 Direct (P2sdb2.dll) - 8.0.0.2 and
> > higher
> > . ODBC (P2sodbc.dll) - 6.0.0.88 and higher
> > . OLEDB (P2soledb.dll)) - 7.0.100.37 and higher
> >
> > NOTE #1: The first 3 database drivers listed above our native drivers for
> > Microsoft SQL Server, Sybase, and IBM DB2 respectively.
> >
> > NOTE #2: The only Seagate Software supplied ODBC drivers that support
> > asynchronous database connection are Microsoft SQL Server and Sybase. CR
> > detects if an ODBC driver supports Asynchronous Query (by testing if the
> > SQL_ATTR_ASYNC_ENABLE flag on the database connection can be seen. If it
> > can, then it will be used (assuming the user has set the asynchronous
> > option).
> >
> > NOTE #3: P2soledb.dll checks the DBPROPSET_ROWSET property from the
> > DBPROP_ROWSET_ASYNCH property set. If this property is set, then the
> > provider accepts asynchronous queries and the option is installed.
> >
> > NOTE #4: The version numbers listed above relate to the versions of the
> > Seagate Software drivers.
> >
> >
> >
> > Support in Seagate Software Applications:
> > ============================================
> > Based on the database driver version numbers above (unless otherwise
> > noted), the following applications and DLLs support asynchronous database
> > connections:
> >
> > . Crw32.exe - Report Designer (at least version CR 7.0.100.15 and SI
> > 7.0.2.100)
> > . Crpe32.dll - Crystal Reports Print Engine (at least version CR
> > 7.0.100.15)
> > . RDC - Report Designer Component for Visual Basic (higher than, and not
> > including, version 7.0.100.15)
> > . Cipe32.dll - Seagate Info Print Engine (at least version 7.0.2.100 of
> > Seagate Info)
> >
> > CAUTION: The "Are you Finished?" message that CR sends to the database
> > server is hard coded to fire off the question for every 1-second interval.
> > This is not configurable.
> >
> >
> > How to Procedures:
> > ========================
> > To enable asynchronous database connections as a general option for new
> > reports:
> >
> > 1. Open the SCR Designer.
> > 2. On the 'File' menu, click 'Options'.
> > 3. Click the 'Database' tab.
> > 4. Select the checkbox 'Perform Query Asynchronously'.
> >
> >
> > To enable asynchronous database connections for existing reports:
> >
> > 1. Open the report in the SCR Designer.
> > 2. On the 'File' menu, click 'Report Options'.
> > 3. Select the checkbox 'Perform Query Asynchronously'.
> >
> > . To terminate a running query in the CR Designer, simply click the stop
> > button located beside the paging buttons.
> >
> > . Once a report has established a database connection, selecting or
> > clearing the 'Perform Query Asynchronously' checkbox will not take effect
> > until the database connection is severed and reestablished.
> >
> > . The SCR Direct Drivers for Microsoft SQL Server, Sybase and IBM DB2
> > automatically set the database connection to asynchronous mode if the
> > 'Perform Query Asynchronously' checkbox is selected.
> >
> > . The SCR Database Driver for ODBC (P2sodbc.dll) will first poll the ODBC
> > driver to determine if the driver in question supports asynchronous
> > database connections. If the ODBC driver supports asynchronous database
> > connections and the 'Perform Query Asynchronously' checkbox is selected,
> > the connection will be set to asynchronous mode.
> >
> > . The SCR Database Driver for OLEDB (P2soledb.dll) will first poll the
> > OLEDB provider to determine if the provider in question supports
> > asynchronous database connections. If the OLEDB provider supports
> > asynchronous database connections and the 'Perform Query Asynchronously'
> > checkbox is selected, the connection will be set to asynchronous mode.
> >
> > Availability: Public
> > Editor:CAL
> > c2006041
> >
> >
> > I hope this helps,
> > Erik L
> > id 848
> >
> > * Please note: If we may be of further assistance with this issue simply
> > reply to this email.
> >
> > You can also check the Seagate Software Knowledge Base for solutions to
> > issues similar to your own. You can find our knowledge base is at the
> > following URL:
> >
> > http://community.seagatesoftware.com/support/kbase.asp
> >
> >
> >
> >
>
> --
> Author: Christine Turner
> INET: Christine.Turner_at_IPS-Sendero.com
>
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Oliver Artelt, System- und Datenbankadministration
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