The Cost Based Optimizer
Posted: Mon Jan 27, 2025 9:04 am
Two main strategies
Why are these questions so important? Because, to put it simply, there are two strategies for processing the data:
1. A big "job"
Here, the question of the amount of data is particularly crucial for estimating the efficiency of the operation.
2. Several smaller "jobs"
The questions about the bosnia and herzegovina telegram screening number of rows ("How often does the small job have to be executed?"), how the data is organized ("How much effort is required per execution?") and caching ("What proportion of the data is already in the cache?") are crucial here.
If the above questions are answered correctly in this context, the appropriate strategy can be selected. Conversely, if the questions are answered incorrectly, it is likely that an inappropriate strategy will be selected, which may be less efficient, lead to longer query execution times and thus also affect other, competing processes.
It is certainly not surprising that Oracle's CBO tries to answer very similar questions in its search for the most efficient execution plan. Interestingly, however, the CBO does not address all three of the above questions to the same extent: The first question, about the number of rows and the volume of data, is covered in detail, and we will see that here too the CBO can be misled quite easily.
Why are these questions so important? Because, to put it simply, there are two strategies for processing the data:
1. A big "job"
Here, the question of the amount of data is particularly crucial for estimating the efficiency of the operation.
2. Several smaller "jobs"
The questions about the bosnia and herzegovina telegram screening number of rows ("How often does the small job have to be executed?"), how the data is organized ("How much effort is required per execution?") and caching ("What proportion of the data is already in the cache?") are crucial here.
If the above questions are answered correctly in this context, the appropriate strategy can be selected. Conversely, if the questions are answered incorrectly, it is likely that an inappropriate strategy will be selected, which may be less efficient, lead to longer query execution times and thus also affect other, competing processes.
It is certainly not surprising that Oracle's CBO tries to answer very similar questions in its search for the most efficient execution plan. Interestingly, however, the CBO does not address all three of the above questions to the same extent: The first question, about the number of rows and the volume of data, is covered in detail, and we will see that here too the CBO can be misled quite easily.