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Breck Carter
Last modified: February 12, 1998
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Tip 77: Sybase SQL Anywhere
Performance Tips & Techniques

30 - Beware Of Slow DDL

SQL usage can be divided into Data Manipulation Language (DML) statements such as SELECT, INSERT and UPDATE, and Data Definition Language (DDL) statements like CREATE, ALTER and DROP. Application programs are usually restricted to DML whereas DDL is used off-line by designers and administrators. Sometimes, however, programs are constructed to use DDL statements as part of regularly scheduled processing and that's where serious performance problems can arise.

A program will be prevented from proceeding if it attempts to execute any of the following statements that affect some table another connection is already using:

Some of these statements can by quite time consuming, depending on the size of the tables affected, and once they start running SQL Anywhere will not process other requests referencing the same tables. In other words, some DDL statements can bring a busy server to an effective halt if they're run at the wrong time; e.g., creating and dropping a temporary index on a busy table, changing a foreign key relationship, or adding a column to a table.

CREATE TABLE is not on the list because it doesn't interfere with other users and it doesn't take that long to execute.

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