With Oracle Database 10g, the rule-based optimizer is desupported.
The references to syntax and operations for the rule-based optimizer in the
following sections are provided for reference and are applicable only if youare running
an older release of Oracle.
Rule-Based Optimization
Oracle has always had a query optimizer, but until Oracle7 the optimizer was only
rule-based. The rule-based optimizer, as the name implies, uses a set of predefined
rules as the main determinant of query optimization decisions. Since the rule-based
110 | Chapter 4: Oracle Data Structures
optimizer has been desupported as of Oracle Database 10g, your interest in this topic
is likely be limited to supporting old Oracle databases where this choice may have
been made.
Rule-based optimization sometimes provided better performance than the early
versions of Oracle??™s cost-based optimizer for specific situations. The rule-based optimizer
had several weaknesses, including offering only a simplistic set of rules. The
Oracle rule-based optimizer had about 20 rules and assigned a weight to each one of
them.
Pages:
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258