Specifically: http://www.verydemo.com/demo_c158_i56898.html
A correct index may increase efficiency by a factor of 10,000, while an invalid index may waste database space and even greatly reduce query performance. Indexing is the most effective way to improve data query, and it is also the most difficult technology to fully grasp, because the correct index may increase the efficiency by 10,000 times, while the invalid index may waste database space and even greatly reduce the query performance.
Index management costs
1. Disk space for storing indexes
2. Index maintenance generated by performing data modification operations (INSERT, UPDATE, DELETE)
3. Additional rollback space is required during data processing.
Actual data modification test:
A table has fields A, B, C, and inserts 10,000 rows of records at the same time
The average completion time without indexing is 2.9 seconds
The average completion time after indexing the A field is 6.7 seconds
The average completion time after indexing the A and B fields is 10.3 seconds
The average completion time after indexing fields A, B and C is 11.7 seconds
From the above test results, it can be clearly seen that the impact of indexing on data modification
Indexes are sorted by storage method
B* tree index
B*tree index is the most commonly used index. Its storage structure is similar to that of a book. There are two types of storage data blocks: branch and leaf. . Both general indexes and uniquely constrained indexes use B*-tree indexes.
Bitmap index
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