Delphi Russian Knowledge Base
DRKB - это самая большая и удобная в использовании база знаний по Дельфи в рунете, составленная Виталием Невзоровым

Avoiding server side locking (including DEADLOCK)


What can I do to help avoid server side locking (including DEADLOCK)

problems when working with Microsoft SQL Server (DBLIB) and Sybase

SQL Server (DBLIB)?

The following suggestions may help you tune your application and

server.  The server side suggestions may not apply to all server

and database installations.

From the client application you may want to take greater control

over the size of results sets (this may mean using TQueries),

minimize the length of transactions (usually not an issue if the

SQLPASSTHRU MODE is set to ...AUTOCOMMIT), and only open dbaware

controls when necessary to help minimize resource drain on the

server and, possibly in this case, deadlock potential.

The means by which the BDE selects data from each of the supported

servers does not make assumptions about how each server chooses

to ensure data integrity.

Delphi/BDE suggestions:

Work with smaller result sets (TQueries, server views, etc.)

also see above form more info.

Check the SQL Links MSSQL Driver "TDS Packet Size" param

making sure that it is set to, at least, 4096.

Minimize the length of transactions.

Investigate creating appropriate indexes.

Filter results before opening a dataset or use tqueries

(live or otherwise) to limit the number of rows selected.

Investigate using the BDE SQL PASSTHRU MODE parameter

"NOT SHARED" (please see BDEADMIN.HLP and BDE32.HLP for

addtional information on the SQL PASSTHRU MODE parameter)

Please note:

BDE/SQL Links 4.01 will not only detect and raise a deadlock

error but it will "reset" its database transaction state when

it detects an MSSQL error 1205. It is not necessary to rollback

the explicit transaction (Database1.rollback) after the

deadlock has been detected.

The error 1205 signals to the client that the server has

"resolved" a deadlock and chosen one of the users to end the

deadlock. This user's transaction is automatically rolled back.

Please refer to the MS SQL Server documentation for more

information on deadlock detection and server error 1205.

MS SQL and Sybase Server topics: (the following is by no means a

comprehensive list. Please check your Sybase and MS SQL Server

docs for tips on optimizing your server and databases)

Create indexes on the remote tables where possible (the

server may require more locks for unindexed tables.)

TEXT and IMAGE columns can take up more pages (columns

can be omitted from a SELECT statement if working with TQueries

whose REQUEST LIVE property is false)

page sizes on the server can be adjusted to better match

expected row sizes (this can help prevent the server from locking

adjacent rows.)

The server will create a table lock if the LOCK ESCALATION

level is reached (part of sp_configure)

Please also see:

MS SQl Server documentation (printed or Books Online)

If using TQueries:



For more information on the options above:

Analyzing locks Topic

(also see Database Developer's Companion Errata)